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OVerheating Engine, Part 2

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CaboJohn

Regular Contributor
I am starting another thread since we are moving into part 2. All the history is on the previous posts and thank you for the assistance you have provided. Went to the boat today for dock side tests and learned a lot. To review the situation: Pursuit 3000, 5.7 liter Captain's Choice, 1992, fresh water cooled, 300 hours, overheat on starboard engine, sometimes shows on gauge, sometimes on alarm with no over temp shown on gauge (sensor for alarm is on the other side of manifold). In the course of treatment have had trained mechanics install new raw and fresh water pumps, new thermostat, cleaned heat exchanger, new belts. I discovered belts were incorrect and caused pump slippage (twice, put on by two different “Crusader mechanics”) and that the seat for the coolant cap had a ding that allowed an air leak, so that gas could exit while running sea trials, and that coolant did not feed back in on cooling. These two issues are resolved, but they interacted with the third, mystery issue and have caused some very conflicted data.


Overheat shows up as a hot spot in the front of the engine by #1 cylinder. Entire engine seems nominal (160) except there where I read 210 on the surface of the manifold. Since that is near where the ECU sensor is located it sets off the alarm. Gauge sensor on other side is fine now that fan belt slippage is resolved. Everything pointed to a combustion leak as the third issue. Tried a combustion gas detector today. Engine overheats quickly in that corner as rpm are raised, lots of bubble and boil....but no combustion gas. (I think that is good news). So I must have some sort of a blockage that is allowing very low coolant flow to boil in that corner, even though 8 inches away the gauge sensor (and my IR reader) show normal temps. I look at the diagrams and realize that the water pump has two exits into each side of the block, and the overheat is by one of the exits. And while the area around #1 is overheated, moving a few inches back on the engine is seems to be gone. So I am thinking some additional coolant must be coming over from the other side of the block. (Can someone help me here, does that make any sense?) The casting temperature over thermostat housing (located on the front in this engine – does not agree with my book) is at 160, pipe at rear of the engine into heat exchanger is 165-70 or so, Exhaust manifolds are around 170, risers at 95, in short everything looks OK.....except for the hot spot.


So I am thinking I will take the new water pump off and see what I can see...maybe a crooked gasket or something blocking an exit. My boat partner (who is too tall to fit into the engine compartment) says try taking out the thermostat. Now the coolant flow is (I think) from the water pump into the block and heads (where we have the problem on that one side), then back out the front to the bottom of the thermostat housing, then though the thermostat and out to the exhaust manifolds, then to the heat exchanger and back to the water pump. The thermostat is downstream of the “blockage” so how can taking that out help? Plus I had received two face fulls on coolant already and was not in the mood for suggestions. Still, I tried it and problem gone! (sort of). Temp in the “hot spot” gradually climbed to 180-185 (not the usual 210), then I check the temp into the heat exchanger and it was at 185 as well (not the usual 165-70). We kept the rpm cranked up to around 2500 and then suddenly the temps dropped everywhere to the 150 to 160 range. Then my IR sensor ran out of battery and I could not take any more readings. But all seemed good and we did not get an alarm.


I took the thermostat home, as well as the one that was originally taken out and replaced. Both open as designed at 160. They are not the problem, but maybe taking them out relieves the symptom. Or maybe taking out the thermostat relieved some back pressure on the water pump and it pushed though (to somewhere) whatever was blocking that flow in that location. That could account for the apparent temperature drop before my IR thermometer ran out of juice.


Sooooo, tomorrow if I put a thermostat back in and everything is good, then I guess I assume I had a blockage and it is cleared, and hope that it does not come back, or lodges where is does not matter, or the water pump ground up whatever it was, or whatever. I can't pull the engine to look for something that seems to be gone. That is an easy choice.


If I put in the known good thermostat and find that the overheat comes back, I guess I have a mystery blockage. I can check the water pump exit for something obvious. If that does not pan out, then what? The engine temps seem fine without any thermostat, and I guess one would assume the higher flow without having one in there is allowing enough coolant to reach my old hot spot in the front corner of the engine. Or is this being overly optimistic? Do I tear into the engine, or just run without a thermostat? Does anyone know of issues associated with coolant not circulating correctly if the thermostat is absent? Winter down here might get down to 65 so cold weather operation is not a problem. Clearly the thermostat is, even when open, a big restriction to flow compared to an empty hole so this could change flow paths significantly.


I will let you know what we find, but suggestions and ideas are welcome. (Partner says leave it all alone and lets go fishing, we have missed too many days already!)


Happy New Year (and I am really glad I will not be pulling the head of the engine tomorrow!)


CaboJohn
 
I see you did the combustion gas test, But, Did you check for an immediate pressure increase in the coolant system with the engine cold and the rpm's raised? This is the most important test.
 
Hi CaboJohn:<BR><BR>I have been following this thread for a while and feel your pain. I think you can pretty much rule out the exhaust leak into the coolant because that sort of thing won't come and go; every time you run the engine hard with exhaust leaking into the coolant (e.g. bad head gasket) the engine will overheat (don't ask me how I know).<BR><BR>I'm not a big fan of the air pocket in the cooling system theory either.<BR><BR>I think you have an obstruction in the internal cooling passages, posibly due to a foreign object floating around in there. This certainly fits the come and go nature and might well be affected by things like themostat removal, water pump removal, coolant inspection, etc.<BR><BR>A friend of mine had an intermittant overheat on a brand new Crusader 454. Engine temp. would be close to normal one day then spike the next. Many parts, hoses, gauges, belts, and pumps were changed, some several times. The typical trial run would look good for a while but the problem always came back, and with a vengence. It got to the point of utter desparation. And then dumb luck intervened. With most of the coolant connections off the engine he happened to peer into the engine and saw one of those orange plastic plugs floating around in the coolant. The mechanic who installed the motors had driven a screw driver through it to remove it but knocked it into the engine instead. <BR><BR>You may have something floating around inside the engine that is causing the bad behavior.<BR><BR>Best wishes,<BR><BR>Tom
 
Guys, thanks for your suggestions. Went to the boat today with new battery for the IR temp gauge. Plan was to put on a pressure gauge (a la Chris) and see if we get a cold start, high rpm pressure jump. No gauges available in town that are not 0-100psi and that did not look like it would show much on a max 7 psi system. So we fired up to see if yesterday's magic healing was still in effect. It was. After warmup, temps on "bad" engine, at the old 210 "hot spot" were 145 (with no thermostat). Lots of cooling going on.

Incidentally, I studied the flow diagrams on the internet last night. Coolant flow splits at water pump, goes down each side of the block to the back, comes to the front though the heads and exits into the passage in the front of the intake manifold (at my "hot spot") where it rejoins flow from the other side of the engine to enter the chamber below the thermostat. The thermostat acts as a big flow restrictor but some flow goes though the three holes predrilled in the thermostat and then is split again where half goes to each exhaust manifold, then on to the heat exchanger and back by a single line to the input of the fresh water pump. When the thermostat opens, nothing changes except that there is less restriction and the flow increases in the entire system. NO new flow paths. This may be obvious to most of you but was not to me. So both sides of the engine are in essence cooled independently from separate flows from the fresh water pump, and I had a hot side and a normal side to the engine...my "hot spot" being the exit point for the coolant from that side of the engine (and if it was caused by a combustion leak it could be any cylinder on that side, not just the closest as I assumed). That one side of the engine is hot and one is normal is a fact as proven repeatedly by the IR gauge. What is important, is that the many things that are generally suggested about overheating (raw water pump/flow, fresh water pump/flow, collapsing feed hose, bad thermostat, belts, heat exchanger restrictions, wrong coolant mixture, etc.) do not just effect one side of the engine and not both sides. So our alternatives are few. Either low flow on the hot side (compared to normal), or more heat being generated on the hot side compared to normal (i.e. a combustion gas leak).

But now, with no thermostat, and presumably higher flow rates, I have two sides that run very similar (both cold). I know something has changed but don't know what. It did seem yesterday, when we did it, heat was starting to build on the "hot side" (I think it got to 180) and then suddenly went down. Maybe that piece of "plastic" Tom suggested has moved now that I have more coolant velocity. Whatever it was, we decided to take the boat out to sea today. At every speed, everything was great. Temp coming out of either head barely got to 155 and that was when we pushed it WOT. Port engine, with thermostat, held at 165 all day under all conditions. Most of the time the "bad starboard engine" was reading 130 since we were just running about 2800. I suppose that now I need to run it hard and look at the coolant overflow tank when underway, since it may show bubbling if there is a combustion gas leak. With all the cooling I have I know there should be no fluid boil going on. Then again our imported combustion gas detector could not find any combustion gas, so I am inclined to believe that previous activity (that filled my face!) was boiling fluid, not combustion gas (stuff tastes terrible, kind of sweet with a real bitter aftertaste...but that was yesterday). Our wives came aboard and we had a great afternoon......they were happy, wine and cheese, etc. and I did not want to look at those d_mn engines so I don't know what was happening but the gauges looked good! I will look a little closer when we fish the boat on Thursday. And then I plan to put the thermostat back in next week to see if the old problems return, or whether in our (slowly reducing) ignorance we have somehow lucked out. But frankly, I have trouble believing this is over. I will let you know what happens.

Keep those comments coming and thanks for your help.

CaboJohn
 
John,

The reason this test is so important: You can have a compression leak into the coolant system on the initial start up only until a little heat is generated and then it stops. Problem is, now you have an air bubble in your coolant system. The reason your problem is resolved while running with the t-stat removed is the water is now circulating constantly and the bubble is dispersed. I would not run your engine with out a t-stat. The engine has to get close to 160 degrees to burn off condensation.
 
Chris,

As I say I don't believe it is over and we will run the suggested pressure test. Although I may have to wait until I go to Phoenix later this month to pick up the gauge, unless I can find one in San Lucas. I suppose you are right about the condensaton, but it is warm here and I am not worried about any short term problems...and eventually I will get the thing right somehow. Exhaust manifolds are a little above 165 until we idle in, and risers and then exhaust pipes and mufflers (where cars have problems) have sea water in them so that is a different issue anyway. Weather is great, but due to some scheduling issues we have put off the next trip for a few days, so no more news for a while. .......And in case you missed the key comment yesterday, wives are happy.

CaboJohn
 
Good luck ,John, when you re-insert the T stat. However, I'll bet it was nice to just use the boat without the troubles for once,and if you think about it for a minute, isn't just about everything we do geared toward your key comment. Have a great New Year....Lee
 
Paradise West. I like that.

We have been fishing the boat once or twice a week. Everything is great (with the thermostat out) as the high coolant flow covers up whatever is the underlying problem. Have had good fishing luck, a lot of dorado (mahi-mahi), some sierra mackeral and I got our first marlin hookup two days ago. Also have done the whale watching trips with guests.

I did learn that the engine is really, really hard to burp and likely never was truly without air. I spent over 30 minutes several weeks ago burping by squeezing hoses to get big bubbles up, then adding 4 oz. and doing it again. So today we put the thermostat back in, and burped for about 40 minutes (run engine a little and add until stable, stop, squeeze hoses and burp some more, etc. etc. until every squeeze was rock solid fluid comes up with no air at all). Hopefully, that was the last of the problems and now it would cool! Then fired it up and monitored temps with the gun and as before the inboard bank on the starboard engine overheated. Nothing changed.

Tomorrow I take out the thermostat again to get my coolant flow up and make the boat functional. But guys, my boat partner says he is done. He is not afraid to run it forever w/o a thermostat. It looks kind of funny with one gage showing about 125, but it runs really good. Frankly we are down to unexplained coolant flow restriction on that one cylinder bank (that means tear the engine apart) or a combustion leak (that has not shown up on the combustion gas detector), and that means tear the engine apart. He is not sure he wants to know and thinks we can live with it as long as the thermostat is out. As for the concern about condensation, we can up our oil change schedule and wait for the engine to fail, if it ever does. It could very well run longer than I can.

I still plan to pick up a pressure gage in Phoenix when I go up this weekend so I can run Chris's "final" test. But at this point the answer may be more to satisfy my curiosity than to plan the next step. We shall see. If we do not get his predicted pressure jump, then clearly it must be a flow restriction, unless someone has another suggestion.

I have learned a lot of useful stuff about cooling systems which I will write up and pass along.

Again, thanks for everyone's help. I wish I had better news, but at least the boat will be up and running.

CaboJohn
 
I'm starting to think your circulating pump impeller (not the raw water pump impelller) might be worn out somehow.

Please keep us informed!

Jeff
 
fastjeff said:
I'm starting to think your circulating pump impeller (not the raw water pump impelller) might be worn out somehow.

Please keep us informed!

Jeff
Click to expand...

I have heard of a coolant pump "wearing out" its impeller, but I've never actually seen one. My 454 coolant pumps are some 30 years old, and haven't even leaked, much less worn out the impeller.

In any case, having an IR thermometer may reveal a clue. I have IR measurements that show a 70 degree nominal drop in coolant temp as it passes thru the HE (at 3200 rpm cruise). 183 deg in, 112 out. Seems to me if the coolant flow is down, then the range will increase even more. That is, if John puts back the 'stat, and runs to near his overheat condition, a low flow might result in lets say 210 deg in and 100 deg out. This would assume normal RW flow rates. The engine coolant is "dwelling" in the HE longer, and gets cooler than what is normal. Inside the engine, the low flow picks up more than nominal heat from the engine, and the temps rise to overheat.
I think putting in the 'stat to run this test is far easier than pulling the coolant pump from the front of the engine, and inspecting the impeller. On the 454, you need to also remove the impeller cover on the actual pump as well.
 
The engine has a new pumps for fresh and raw water, new belt, new themostat (when it is in), and a clean heat exchanger. The problem is only in one cylinder bank. The earlier thought I mentioned on the fresh water pump removal and check was that that is the point where the coolant flow splits, with one pump exit going to each side of the block. Flow comes back together at cavity below the thermostat. So issue is between these two points. Everything else looks good.

CaboJohn
 
John, with your degree in thermodynamics, you'll understand what I'm about to mention.

IMO, we should not be operating an engine without a thermostat, period. The stat is what controls internal engine temperature.
If the stat must be removed to prevent over-heating, something else is wrong!

The thermostat's job is to "hold back" coolant (i.e., sea water or E/G mixture.... in your case; E/G) and to release the coolant on an "On-Demand" or "As-Required" basis.
The Circ Pump''s job is to mildly pressurize the engine block/cylinder heads in order for that thermostat to function as such.

Take heed of Jeff's comment re; the circ pump impeller.
While it's rare to see one fail on a closed cooling system, never say never!
The impeller itself may be OK, but perhaps it's fit onto the shaft is compromised somehow.
Cost to check this is a bit of your time and several gaskets. Basically, it's free!
BTW, this DOES NOT require the more expensive Marine version Circ Pump for a Closed Cooling System.
The automotive version short shaft circulating pump will not know that it's been installed on a Marine engine, unless you tell it! :D

The other concern would be enough sea water passing through the H/E's tube bundle, and "Un-Restricted" on to the exhaust system.
Have you checked the E/G side of the tube bundle? (the side around the tubes where the E/G circulates)
Any rust scale build-up?
Have the ID of the tubes been rodded?
Any interior delamination of the "spent sea water hoses"? (rare, but it does occur)

diver_dave said:
I have heard of a coolant pump "wearing out" its impeller, but I've never actually seen one. My 454 coolant pumps are some 30 years old, and haven't even leaked, much less worn out the impeller.
Click to expand...
An impeller can also wear the pump body and the impeller cam.
(I mentioned this in post #28 of your other thread)
Add a bit of silt throughout the season, and you have wear.
Throw in a few years of this, and...........................

Not that I have the ultimate resolve for you, but in post #28 of your other thread, I touched on what Chris suggested regarding a quick fire up and quick RPM increase to 3k, and to watch the cooling sytem pressue.
Have you done this yet?
Is your recovery system reservoir maintaining a constant volume?



Keep at the P of E..... and you'll find it!

.
 
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Thanks, Chris for the offer. I will be in Phoenix Monday and Tues. and will pick up a 0-15 lb. pressure gauge, or if I can't find one (a simple gauge I can put in the sensor hole is about $25), then I will spring for a real cooling system gauge. In any case, then we will look for the cold engine, high RPM spike you believe will indicate a combustion leak. IF we find one (remember the combustion gas test was negative), then it is either pull the head and look.......... or live with it w/o the thermostat until it gets worse, or I get too old to boat any more (I figure I have another 20 years so don't hold your breath!). I may make a great test case for everyone that believes no thermostat is a disaster, since we will be running two identical engines in identical conditions, except for the 'stat.

Now as for the suggestions on the impeller, I have new pumps and every sign of great flows and cooling capacity. And actually, I inspected the old pump and it looked good to me, but what the hey, at that point I was not footing the bill. And the new pump was a "marine" version with brass impeller (I asked why and the mechanic said that was the way he did things!) but I agree with Rick it is not needed in a fresh water cooled engine. Oh, and the recovery system seems to be working fine, and I cannot see any bubbling action in it.

The overheating problem, whatever it is, exists between the water pump outlet to the block on that side of the engine, and the head outlet to intake manifold from that side of the engine. All tests and reading confirm that. I have probed the passage though the intake manifold to the bottom of the thermostat housing and it is clear. If it is not a combustion leak creating excess heat in that cylinder bank, then it is low flow on that side of the engine only. So that would suggest something blocking full flow. Because of the restriction, the theory would be that most of the water ends up flowing to the other side of the engine. If that is the case I have a plan to backflush that side of the engine. I will remove the water pump and seal off one of the passages from the missing pump into the block by bolting on a small plate I will fabricate. I will disconnect the exit hoses (that go to the exhaust manifolds) above the thermostat housing and block one of them off. One the other I will put a garden hose connector. Remember the themostat is out. Now I can send water backwards though the head and block and have it gush out of the unblocked hole in the front of the block that the waterpump usually pumps into. And I can do each side separately (by moving the blocking plate) and see if the flows are different. And I can turn up the pressure and hopefully blow out whatever is lodged in the block or head on the offending side. I have terrific water pressure at the dock hose so if it can be blown out, it will be.

Anyway, it's a plan. We shall see.

CaboJohn
 
You must have the remains of an impeller or something lodged in there.

Was this engine ever raw water cooled to your knowledge? Many have tried converting them to FWCooled and had cooling problems from rust builfd up.

Jeff
 
Boat history is in old posts. An '02 with just under 300 hours when I got it. Fresh water from the factory. Engine was pulled last year for a new flex plate installation. Owner had also complained about coolant weep and new manifolds and risers were put on so something could have entered then. Also new belt. Belt was wrong which led to "original" (maybe) overheating (and possible engine damage if they ignored the alarm). In process of running down belt issue (with a "real" Crusader mechanic) we replaced fresh water pump and had heat exchanger off. So something could have entered then. The new mechanic's replacement belt (when the first new one finally gave up) slipped less but was also wrong, believe it or not! Though it all diagnosis was complicated by nick where pressure cap seats. So a lot has gone on.

But I am now left with a cylinder bank that, compared to the three without problems, makes too much heat, or get too little cooling. Simple choices, hard to figure out.

CaboJohn
 
John....just a thought but anyway here goes, when the new pump was put on , was a sealant used on the gaskets that lead to the water jackets i.e. silicone. Could some of it have squeezed out and obscured the passage on the side with the problem ,not completely but just enough to cause the problem. When you leave out the t-stat, it lets just enough water thru to alleviate the problem, but with the t-stat in the combination of the restriction and the t-stat reduction in flow is just enough to cause your troubles. I know it's a long shot but at this point you have me reaching for straws....Lee
 
An obstruction in an internal cooling passage (see post #3) makes sense. Your plan to investigate the flow through each side of the block separately has some merit. It would be nice if you could actually measure flow through both sides, i.e. gpm on each side using a constant and stable water supply. It might be difficult to see the differnces "by eye", and measurement is the foundation of science.


Good luck,

Tom
 
John,

If this issue were mine, I would lay awake at night and stare at the ceiling, most likely while sitting in traffic as well. Once upon a time, a friend of mine was chasing theories on his overheating gas engine after correcting a coolant leak. Long story short...and about 3k parts and labor later, his first repair for the coolant leak was the problem, it was the one item he was confident it couldn't be because it was new. The water pump impeller was freewheeling on the shaft, the engine would overheat at higher rpm's.


Just a thought, to toss into the theory pool.
 
Looks like we have an answer. I picked up a nice pressure gauge in Phoenix and brought it down and installed it in the manifold (in place of the computer sensor). Then did Chris's suggested cold engine test. At idle, no pressure rise. At 2000 rpm I got an immediate rise to 3 psi. At 3000 rpm it went to 4 psi. These numbers held steady, so while I have what seems to be a leak of exhaust gas into the coolant, apparently at the dock (no load condition), the small amount of back pressure can contain it. Pressure drops about a pound when I shut down and then holds, so it is not just water pump pressure we are seeing.


I then warmed the engine up (without the thermostat it is less than 115) at idle. After 15 minutes, still no pressure showing. At 2000 rpm pressure again went to 2 psi. After 10 minutes temps were still under control, with oil at 129, left (problem) bank at 106, right bank at 102, exhaust manifold exit to heat exchanger at 109. At 3000 rpm and 5 minutes the pressure was again up to 4 psi, left bank at 107, right at 101, oil at 142, rest the same. So heating the engine has little effect.


Since the left bank is the issue I repeated tests removing the plug wires one at a time, and then removed them in adjacent pairs. I am puzzled as I still got a pressure rise in each case.


Went fishing the next day. Down here we can start trolling when we hit the ocean (100 fathom line is less than ½ mile offshore) so most of the day was at 1200-1600 rpm. Caught 3 nice dorado and saw lots of whales. When I checked pressure it was always in the 1-2 pound range. On way in we ran about 3300 rpm for 30 minutes or so. This did not look as good. Pressure went up to 6-7 pounds (lot of needle vibration) and there was bubbling in the overflow so gases were being relieved by the 7 pound cap. Engine temp readout climbed to 135 but the gun showed that same temp at each bank exit so everything was under control. And, as always, each engine performed perfectly. It was a little rough for a WOT test, but I had done one several weeks ago and the bad engine actually ran about 100 rpm more than the good one, so there is not any loss of power with the problem.


So we seem to have a combustion gas leak. I do not know why it did not show up when we did the combustion gas test, other than perhaps because the leak is so minor at the dock without a load. But even at the dock it is major enough to cause a gas bubble and boiling in the left cylinder bank unless we remove the thermostat and get the high flow on the cooling system. So that is a mystery. And I do not know why removing plug wires did not isolate the offending cylinder and relieve the problem. Another mystery. Any suggestions on answers??


As for the future, I am not overly concerned with the dreaded condensation issues due to running the engine cold without a thermostat. I think whether the oil runs at 140 or 170, any exhaust moisture blow by will cook off, and I also will up the oil change schedule. If the leak problem gets worse we will obviously have to pull the engine apart and find it. I would like to know exactly where the problem is before I do that, so I need to fool with plug wires more. Hopefully I can find it. My real concern is whether delaying dealing with the issue may cause long term damage (erosion, cracking, etc.) that might be avoided by going in now. We can all speculate. Does anyone have any real life experience that might shed light on this question? Any information or suggestions would be appreciated.


Thanks for your responses.


CaboJohn
 
"so gases were being relieved by the 7 pound cap."

Did you do the test for combustion gases? Bubbles could just mean steam.

You are about at that point where taking off the previously overheating head is indicated. There are a couple of fairly small water passages in the head gasket. Since your pressure holds pretty well after shut down, I don't see a smoking gun for combustion gas leaks.

"the gun showed that same temp at each bank exit"

You are shooting the coolant exit from each head? This would be done on the intake manifold, correct?
 
I did test for combustion gas several weeks ago and came up negative. Forum advised that I should do the pressure rise test on a cold engine to be sure. That test was positive. So we have a conflict but the positive pressure test is definitely positive (although I have not pressure checked the "good engine" to insure it somehow does not show a similar rise). The negative combustion gas test my be due to my lack of skill, or the low amount of combustion gas, or whatever. I do not know how sensitive the NAPA kit really is.

Exit temps on heads are measured at front of intake manifold on the water passageways that lead to the the thermostat block in front. These are the same passages that have the ports for the temp sensor for the ECU (on left side) and the temp sender for the gauge (on the right side). That fact that these are measuring two different coolant streams, one from each head, (with the left controlling the alarm and the right controlling the gauge) led to a lot of confusion early in the diagnosis.

No question there was steam when the thermostat was in, coolant flow was low, and the temps built up at exit to left bank to over 212. But now, with all temps low and coolant at 135 or less, I do not believe that steam could survive all the way to the coolant pressure cap, through the overflow hose and into the overflow tank. It would recondense somewhere on the trip. So the bubbles are some other gas.

CaboJohn
 
I don't think the pressure rise you saw was due to a combustion leak but the circulating pump doing its thing. System volume is fixed so with the pump spinning faster, the flow goes up and so will the pressure. You indicated the immediate pressure rise, with increased rpm, and then it held steady. a combustion leak would have caused the system pressure to continue to rise. this is reinforced by the lack of a positive result doing the combustion gas leak test.


I'd be inclined to remove the circulating pump and see if there was tooo much gasket sealer used at the block mating surface
 
Good thought, but pressure remained after shutdown, and I did get pressure relief at cap and bubbling at high rpm underload so it does build under some circumstances.

CaboJohn
 
CaboJohn said:
Good thought, but pressure remained after shutdown, and I did get pressure relief at cap and bubbling at high rpm underload so it does build under some circumstances.

CaboJohn
Click to expand...

John,
Before you remove the gauge, Let the engine sit over night so it is absolutely cold. Remove the pressure cap on the exchanger, Top it off, re-install the cap and start the engine. Push the rpms up immediately and look at the gauge for the pressure increase, then shut the engine down, before heat builds, and see if the pressure stays. Do this test with the t-stat removed. If the pressure goes up immediately before any real heat is generated and stays up after shut down, you have a leak.

To find out which cylinder it is, you will need a compression gauge adapter with the schrader valve removed and a compressed air supply with about 130PSI. This test must be done on a cold engine. Remove all the spark plugs, remove the valve covers, loosen the rocker arms, make sure your coolant is topped off and the cap is secured. Now pressurize each cylinder and look at your gauge for an increase.

BECAREFUL! The compressed air will spin the engine over until the piston hits bottom dead center.
 
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Thanks Chris. I have done the cold test and as I posted got 3psi at 2000 rpm and 4 psi at 3000rpm within 5 seconds of startup. Both no load (neutral at dock). Pressure did not go higher but at no load combustion pressures are lower and it must be a very small leak. And as you may have read, at 3300 rpm under load we get lots of activity and pressure went to 7 and relieved very quickly.

I will see if I can cobble something together to do the compressed air test and find the bad spot.

I don't suppose speculation is productive but what is your bet, a head gasket or a crack in the head or block (ouch)?

Have you any advice on the dangers of future damage if we run it this way for a while? I really runs great and fishing is good!

Thanks for your help.

CaboJohn
 
John,

Pull the head and look! In an hour or so you can have the head off and see for yourself, before you end up with a bent connecting rod while running tests 3300 rpm. It's not all that uncommon for the 5.7's to do just that, then this minor problem becomes a serious event, with a much bigger can of worms to deal with. Fishing might be good, but if you are running this sore engine at planning speed, those fish might end up rather expensive by the pound.

Order an upper gasket set, to have on hand, and if it needs a head 500.00 or so should cover a replacement if needed.

Nothing is ever free in Waterworld!
 
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Reverend Bob said:
John,

Pull the head and look! In an hour or so you can have the head off and see for yourself, before you end up with a bent connecting rod while running tests 3300 rpm. It's not all that uncommon for the 5.7's to do just that, then this minor problem becomes a serious event, with a much bigger can of worms to deal with. Fishing might be good, but if you are running this sore engine at planning speed, those fish might end up rather expensive by the pound.

Order an upper gasket set, to have on hand, and if it needs a head 500.00 or so should cover a replacement if needed.

Nothing is ever free in Waterworld!
Click to expand...

I agree with Reverend Bob, After you pump the cylinders full of air and find which one is leaking, pull it apart right away. Crack or gasket? only pulling it apart will tell.
 
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