Overheating problem

@KAG So what did you find when you pulled the end caps off of the heat exchanger?

CaboJohn

The insides of the tubes were dirty but not blocked. I have cleaned them but have not had a chance to reinstall or test so was holding off posting a follow up. I should know tomorrow and will let you know.

Pulled the heat exchanger. Tubes were dirty but not blocked. Cleaned, reassembled and reinstalled. At 1200, under way, temp tops out at about 140, so is better, but at higher speeds (2900) temp still climbed to over 200, so there is still an issue. ( shut down at that point so don't know how hot it will get).
Should I replace the coolant pump to eliminate that as a possible? Or should I measure the coolant flow first? Any one know what it should be at a given RPM?

Or anyone have any other idea? please....

@KAG - As Bill (our ex) would say, "I feel your pain."

I only have experience with one pair of Crusaders, so hopefully some of the guys that have seen 'em all will chip in with an idea. But, based upon my several months of operating without a thermostat on one of my Crusaders, I would say that your current observation of 140 under load at 1200 rpm is not that far off of what it should be. As the under load rpms go up, so does the heat load produced, but the higher engine rpm also is supposed to move more raw water and coolant, and while temps climb, they should not get anywhere near the 200 at 2900 rpm you have seen. My working assumption would be that in one of the systems your flow is not going up with rpm as it should. So on the raw water side, something to do with the pump could be slipping, or it could be that the water intake, for whatever reason, can't get fed properly at higher hull speed.

On the fresh water side, it could be that the (no) thermostat is coming back to bite you.

When I had mine out, I put a pressure gage after the heads and just before the (missing)thermostat, and at higher rpms got wild bounces in pressure. We were chasing an overheat that went away when we took the thermostat out (but not when the thermostat was replaced or exchanged with the other engine). We first suspected head gasket leaks (accounting for both the temperature and the pressure spikes), but that was not the case. It would seem that the fresh water pump needs some restriction to pump against (our theory). Otherwise it cavitates, or pulses or whatever, and things get crazy. The gage looked so alarming that we would not run the engine over 2100 rpm. In our case it still circulated enough to cool, even at high rpm, but yours may not. The pumping action clearly was not right. As evidence this could be true, there is an often repeated old wives tale in the hot rod industry that running without a thermostat will cause the coolant to circulate too fast and it will not spend enough time in the radiator to cool and the engine can run hot. Those that have a thermo backgound will tell you that explanation is B.S. Still, many of the strange tales you hear may be actual (factual) observations to which they attributed the wrong cause. Perhaps it is not uncommon for pumps not to pump well if there is no back pressure in the system. The hot rodders that don't want a thermostat (but believe the too fast flow theory) put in a large washer in place of the thermostat which gives adequate flow (and also some restriction) but does not have the failure potential of a thermostat. All this being a way of saying maybe now you should be sure you have the correct 160 degree marine thermostat, a working (presumably) 7 psi pressure cap, and try it again with the thermostat in (or if you please some other restriction like a washer). If that makes the fresh water pump work better, this, along with your other efforts may get you over the hump. (As an aside, in our case since we could cool without a thermosat, but were not comfortable with the resulting low engine temps and pressure fluxuations at high rpm, we compromised by putting a few extra bypass holes in the themostat. Works great, no pressure gyrations, and the additional flow keeps temps close to correct (a little low) at lower rpms, and spot on at cruise.)

Other than that, I am kind of dry on ideas. Since it is an older setup, I would make sure that the engine had the correct heat exchanger, or at least one with sufficent capacity.

And in fooling around, if you do happen to get a true (boiling coolant) overheat, you need to let everything cool down after shut down. I am told that restarting and sending a slug of coolant into a block/head that has soared in temperature because of boiling is the cause of most warps and cracks.

Good luck!
CaboJohn

I agree with John's first paragraph. The sea water pumps are RPM governed, so in theory, when engine speeds and loads increase so does pump volume. This should accommodate for any increased engine temperature demands.
Same with a car or truck...... as engine speed and load increases, so does the circulating pump and air flow across the radiator.


I don't quite understand the thermostat failure rate comment.
IMO, on our Closed Cooling systems, I don't see these offering a high failure rate. If they did, the industry would see to it that measures were taken.
The OEM installs a thermostat for good reason. If these were my engines, I'd definitely want to keep a correct temperature thermostat installed.
The small air bleed holes are there for purging air, not necessarily for a by-pass. If a by-pass is required, we will generally see this incorporated into the T-stat housing.


You asked about replacing the engine circulating pump.
With a closed cooling system, the automotive version can be used, saving you some money. A closed system cooled Marine Engine won't know the difference.


KAG, the one item that has not been discussed, would be the E/G side (the Ethylene Glycol side) of the heat exchanger tube bundle.
If the H/E systems had been installed on previously Raw Water Cooled engines, then there is a good chance that rust scale has finally restricted the outside (the E/G side) of the tube bundle.
This side is not accessible by user Joe, nor can we see the bottom area where the rust scale debris will begin to build up.

However, while the H/E is removed, we can add a cleaning chemical to this side.
With all ports closed off, partially fill the H/E with hot water and a rust scale chemical.
Shake the hell out of it, and dump the contents into a white five gallon bucket.
Repeat this process.
Look for rust scale debris against the white bucket.

If you find that this side is restricted, the H/E will need to be professionally disassembled and cleaned.
No amount of other measures will correct your over-heating issue until this is resolved.

Imagine attempting to add a larger fan blade or larger air shroud around a car/truck radiator that is clogged on the interior.
The clogged interior must be corrected first.

I don't know if this could be part of, or all of your problem, but I thought that it may be worth mentioning to you.

.

any idea what the coolant concentration on the closed side is??

Coolant started the season about 50/50. Everytime I do something and spill a bit I have replaced the missing solution with water so it is now reduced somewhat. I would guess about 30% antifreeze.
I took the thermostat out originally to make sure it wasn't the problem. I left it out because it allowed me to do tests at the mooring. (if it was in the temp would always be at least 160 once it warmed up. Not having it in allowed me to see how cool it would run, which is how I know there was an improvement when I cleaned the tubes.) I wasn't concerned about running without it since the motor was not really running cold. It seems far fetched to me that not having it in could be the problem, particularly since there was a problem before I took it out. But, I am not an expert, which is why I am asking for advice. So I will put it back in, then we will know for sure.
If that doesn't work, I think my next step will be to swap the heat exchangers. That will take the coolant side of the tubes in the HX out of the equation.
If that doesn't work, I will probably either swap the coolant pumps, or replace the one on the hot engine.
If that doesn't work, I might buy a sailboat.

Imay be repeting a replay. reman engine may have wrong gaskets, or gaskets installed wrong.

@KAG, @Rick I got a little wordy on the last post, but my point was that whatever has been done seems to have the engine about where it should be at 1900 rpm and no thermostat. The problem is at higher rpms. There is reason to believe that a coolant pump may not circulate well at high rpm without some restriction in the system to keep the pressure up from the exit of the pump though the block. Maybe that is true, maybe not, but putting the correct thermostat in at this point is a logical next step (and I also like swapping the heat exchangers if that does not work).

I have never even met anyone that had a thermostat fail so I agree with Rick about the likelyhood of that. Still the roundy round racers worry about it. They even have "no fail" thermostats that are designed to fail in the open position. And, as I said, those that do not want a thermostat at all still put something in that slows down and stabilizes the flow. So the thermostat may be one of those things that has a secondary purpose as well as a primary purpose. I know by observation it stabilizes the pressure spikes we were seeing.

As for the holes in the thermostat, in the case of my engines (5.7 MPI Captain's Choice) it is a story of two purposes. Yes the holes are to vent air and in fact many hot rodders put a small one in just for that purpose. But all engines need some way to circulate coolant at a low flow when the thermostat is closed. Otherwise by the time the stat saw enough heat to open the block would be boiling. In cars, the heater circuit does this (as a secondary purpose). In some Crusaders they do have a second passage built into the themostat housing. In some Crusaders with the thermostat on the heat exchanger there is a bypass that is open when the thermostat is closed and when it opens "normally", but is closed off in high heat conditions so that all the flow goes though the HX. In my engine they have gone the KISS route, and have no bypass but have three holes in the thermostat, both so the system will burp trapped air when the thermostat is closed, but also to provide the coolant flow needed by the lack of a bypass.

I don't know what kind of system KAG has.

Although I did use the car/truck radiator analogy earlier, let's not compare our marine engines to automotive.......... apples/oranges.

Let me shout this out in a rather gruff fashion, as though we are all good friends sitting down together having a beer or coffee.

First, and not necessarily in this order....., leave the thermostat installed.
To remove it, simply circumvents an otherwise different issue. Find the cause outside of this, and make the necessary corrections.

Secondly, a good working cooling system should and will function throughout all RPM ranges.
IOW, I'd not shoot for corrections that affect one RPM range only. That simply continues the circumvention of the real issue.

Thirdly, there are two sides to a H/E (heat exchanger).... the sea water side, and the E/G side.
You'll have what's call a "shell and tube" heat exchanger, and you may not have the baffles that are shown here.
Your coolant in-lets/out-lets may also be positioned differently.
However, your sea water in-lets/out-lets will be very similar to this one, and may make multiple passes.




Apparently your sea water side is free and clear.
Example of the sea water side... (aka interior of the tube bundle, or tube ID).


If the exhaust manifolds are also free and clear, this side should be functioning correctly.

However, if the inside of the H/E shell (the actual tube bundle exterior, or OD of the tubes) has rust scale debris building up around the tube bundle, it will likely disable it from doing an efficient job at removing heat from the E/G coolant.

You can force all the sea water through the interior of the bundle that you want to, but if the exterior of the bundle cannot remove the BTUs from the engine coolant, you'll have an over-heating issue, plain and simple......... stat or no stat!

Do the white bucket test, and see what you get from it.
Or... take it in and have it professionally cleaned out and re-assembled.


Now, will you please pass me the beer pitcher?

.

I don't want to distract from the overheating issue but since there has been some question about my thermostat set up i am if I did it right) posting a picture of it. There are two capped openings, which are different sizes. They have been that way for as long as I have owned the boat so the set up is not the problem. I don't know what they are for. I think the engine was originally raw water cooled and they may have been in use then.

KAG said:

I think the engine was originally raw water cooled and they may have been in use then.

Click to expand...

Bingo, and a possible red flag!

Bingo in that this may point to rust scale that has dislodged itself from this previously raw water cooled engine, and has now found it's way to within the tube bundle exterior. This does become an issue when converting a previously raw water cooled engine over to a closed system.

Red flag in that an open system T-stat housing is very likely incorrect for a closed system.

Your image did not work for me.

.

KAG, can you re-post the image of your T-stat housing for us, and perhaps a few photos of the Heat Exchanger?

.

I don't know why the photo didn't post. I am going to have to get one of my kids to help me out with it.
Rick: my boat is a 1984. A couple of years ago I ran into the daughter of the former owner, who recognized the boat. She told me it was originally raw water cooled and that her father had installed the cooling system. So it operated with the modified system for over 20 years. This spring while it was all apart I flushed and backflushed the HX. When I pulled it a week or so ago and cleaned the tubes I put some vinegar in the coolant side, let it sit for a while and then flushed it again. I doubt there is any rust or whatever in there. Also, don't forget that I just put in a remanufatured long block. I don't know its history but the block that was raw water cooled all those years ago is gone. It is possible there is some scale or something on the outside of the tubes that needs a stronger chemical. So I don't think the system is stock and it is possible that it can be improved, but it did work fine for a long time.
This morning I went out and reinstalled the thermostat. I did not have time for an extended test but it appeared that the temperature, at 2900 rpm, topped out at about 195. So again better, but not right. When I increased speed the temp started to climb, but I didn't have time to see how far. I never would have expected putting the thermostat in would keep it cooler and am very grateful for the, shall we say suggestions, that it be put back in.
I will try and post some pictures tonight but, unless someone comes up with something else, I think my next step will have to be to exchange the exchangers, which will have to wait until the weekend.
BTW, not that it should matter, but the raw water enters my HX at one end, travels down half the tubes, gets turned around and exits at the same end it entered. The coolant goes in one end and out the other.
Thanks again for all the input and suggestions. I feel that I am making progress. (painfully slow, but any progress is way better than none)

Just an additional two and one half cents here.

KAG said:

I don't know why the photo didn't post. I am going to have to get one of my kids to help me out with it.
Rick: my boat is a 1984. A couple of years ago I ran into the daughter of the former owner, who recognized the boat. She told me it was originally raw water cooled and that her father had installed the cooling system. So it operated with the modified system for over 20 years.
KAG, unless these have been professionally cleaned at one time, that represents a potential XX years of rust scale debris build up.
I'm not suggesting that this is ultimately your issue, but it is certainly a possibility.

This spring while it was all apart I flushed and backflushed the HX. When I pulled it a week or so ago and cleaned the tubes I put some vinegar in the coolant side, let it sit for a while and then flushed it again. I doubt there is any rust or whatever in there.
Well, I still suggest that you have the H/E's cleaned out professionally. Chemicals will not always adequately remove the rust scale, whereas disassembly and cleaning will.
I know that this represents yet one more cost, but you can then remove this from your P of E list, and move on to a few other items, if need be.

............. unless someone comes up with something else, I think my next step will have to be to exchange the exchangers, which will have to wait until the weekend.
As in swapping the Port side H/E to the Stbd side???
That's one of the beauties of having twins..... we can swap some parts as part of our P of E.


BTW, not that it should matter, but the raw water enters my HX at one end, travels down half the tubes, gets turned around and exits at the same end it entered. The coolant goes in one end and out the other.
That would mean that these are double pass on the sea water side....... this is good!

Thanks again for all the input and suggestions. I feel that I am making progress. (painfully slow, but any progress is way better than none)
Yes, it sure is!

Click to expand...

A pic of the HX, in addition to the T-stat outlet, would help...also, any idea as to the old vs new engine/block that was recently replaced?

I can't get the pictures I took (with an ipad) for this to post, so am trying some old ones I took with a camera. If posting them works I will take new ones (more specific to the thermostat and cooling system) with the camera and post them. These are shots I took of the old motor when I was taking it out. Everything looks the same now but I don't know that you can see what you want to in these. the first should show most of the cooling system (without hoses). You can see the thermostat housing in the second one but the heat exchanger is gone.

KAG, I'm not understanding what looks like two heat exchangers. Perhaps you can explain this.

I think that your T-stat housing has been adapted from a RWC system T-stat housing. Two ports are apparently closed off.
I'm also wondering if the steel plumbing parts, and the number of bends and elbows, are restricting coolant flow.
The corrigate Circ Pump supply hose may be somewhat restrictive.... not sure, but these are usually smooth pre-formed suction hoses.
The exhaust manifolds are in the CCS loop, but I do not see the return-to-H/E lines.

All in all, it looks like an overly complicated closed cooling system to me.

KAG, I need to preface this a bit: I am not familiar with your system. I am, however, familiar with the Closed Cooling Systems in general.... and certainly with the RWC systems.



see first attached image at bottom of page:

A and B would have been for the raw water leaving the engine as per what the thermostat dictates.
These are NOW for the coolant-to-exhaust manifolds (according to the hose routing in the other image).
Let's hope that between these two ports, that they are dividing coolant flow equally.
(again, I do see any exhaust manifold-to-H/E coolant return hoses)

C would have originally been the Raw Water supply.

D would have been the Circ Pump suction hose connection.



see second attached image bottom of page:
(it's not quite the same as yours, but the internally porting should be very similar)

The issue with an "open" system T-stat housing (now being asked to work in a CCS) is the way in which these are internally ported.
With a RWC system, the T-stat housing allows most all sea water to by-pass actual engine cooling demands, and directs most of this into and right out the exhaust system. (this occurs within what may be called a mixing chamber)

The engine Circ pump is constantly pulling on the large port (D), wanting to "charge" the engine block with cooling water.
The actual thermostat allows the water to leave the engine block/heads as required...... (very much like with a CCS)
I believe that your T-stat housing is actually designed for RWC'ing.
Blue = incoming sea water
Yellow/blue = water from the mixing chamber going to the Circ pump
Red = tempered water leaving the block/heads
Red/Blue = tempered water mixing with by-passing sea water going to the exhaust system


I don't know what affect this additional porting may have on your CCS, but IMO, there is no need for ports C and D in your system.
Also....., I'm not suggesting that this is your over-heating issue, just say'n that I don't believe that this is the correct T-stat housing to be using on a CCS.

I would have expected to see a T-stat housing more like this one.

Rick: I tried again this morning to post better pictures. Since old pictures in my computer taken with a camera posted, I tried taking pictures of the pictures on the ipad, didn't work (wouldn't post). I have two teenagers and none of us have yet to figure it out.
Anyway, I think you are right, the housing is a carryover from the old system, but seemed to work fine. With those ports (your c & d) blocked wouldn't it function the same as the one you pictured? In your thumbnail two posts up you mention that the return to the pump from the H/E is usually from the lower port. Mine doesn't have a lower port. Coolant enters the top at one end and exits the top at the other end.
Hoses (missing from the picture) run from the aft end of the exhaust manifolds to the H/E, which has two parts. The top cylinder, where the hoses connect, simply collects the coolant, which then gravity feeds into the lower one, which is where the tubes are and the actual cooling takes place. Elbows etc. are steel (good eye) but all the ones I have examined are clean, with no rust or corrosion (in or out). The cooling system has always seemed to me to have an inelegant, homemade appearance, but worked. Maybe it is marginal and, because of the way it is made (hose sizing, ribbed hoses...?) everything has to be perfect, so if the tubes are a little dirty, or whatever, the engine runs hot. If so, I have to figure out what else isn't perfect, or redesign or replace the system.
On the sea trial when I bought the boat (7 seasons ago) this engine was running hot. Part of the deal was that the H/E be cleaned. I don't know what was actually done but the temps were fine when I took delivery.
I don't see why it would matter but feel I should mention that this engine is reverse rotation.

KAG said:

1.... Anyway, I think you are right, the housing is a carryover from the old system, but seemed to work fine.
With those ports (your c & d) blocked wouldn't it function the same as the one you pictured? In your thumbnail two posts up you mention that the return to the pump from the H/E is usually from the lower port. Mine doesn't have a lower port. Coolant enters the top at one end and exits the top at the other end.

2.... everything has to be perfect, so if the tubes are a little dirty, or whatever, the engine runs hot. If so, I have to figure out what else isn't perfect, or redesign or replace the system.

Click to expand...

1.... OK.... so if I understand you, the upper unit is serving as an expansion chamber or a coolant reservoir only.
The lower unit is the actual Heat Exchanger with the tube bundle.
Looks rather small for what's called a "Full Closed System".


None of my biz..... but I don't like seeing those galvanized steel pipe pluming parts, nor the amount of bends and elbows, nor the corrugated circ pump suction hose being used.
From my limited Hydraulics/Pneumatics experience from years ago, small ID, bends, elbows, distance and perhaps corrugated interiors = flow resistance.

Question: Are these OEM Crusader patterned systems, or are these a home version?


As for the T-stat housings..... your call on that.
If this was mine, I'd be changing them.

The engine being a RH Reverse Rotation means that the Circ Pump must be RH Rotation capable.
These are centrifugal pumps, and will usually function in either direction.... however, some casting porting causes them to NOT work as effectively for RH rotation.
You can purchase a RH rotation specific circulating pump, or what's called "bi-directional".
This circ pump is either rotation capable. You'd need to look closely in order to see the difference in the castings.


I can't explain why this worked when you first took delivery 7 years ago, and why you are now having trouble. Perhaps things are closing down due to rust scale, etc. Don't know.
I do know that when converting a previously RWC'd engine to a CCS, there are inherent and potential issues that must be addressed, or they will eventually haunt us.
We also know that you need to correct this before you see some serious engine damage occur.

I'd suggest that what ever you do to the RH engine that corrects this issue....., you also do same to the LH engine.



2.... I agree. This is why I suggested the rust scale build up around the tube bundle, and is why I suggested having these serviced.

As for redesigning...... if the H/E is on the small side for a "Full System", is there any consideration that you would remove the manifolds from the CCS loop, and RWC them instead? This would be what's called a "half system".

Here's part of my thoughts;
Your twin SBC engines are undergoing a work load not all that different from other twin SBC installations. We'll see some differences in H/E configurations, but all of these OEM systems are capable of removing the engine produced heat.
It's not too much to ask of your cooling systems to keep your SBC's just as cool as any other systems.... as long as they are up to snuff.

So..... yours are either NOT up to snuff, or there is a design flaw, or possibly a mix of both.


Not up to snuff = sea water pump issue, suction hose collapse, restrictive exhaust water flow, H/E tube bundle issues, etc, etc.

Design flaw = some of this rather unorthodox plumbing, incorrect T-stat housing, undersized H/E, etc etc.




.

It took a day and a half, but I pulled the heat exchangers from both engines and swapped them. The one on the behaving engine had some rusty bits in it. What is really interesting is that when I drained the collection cylinder on top and the hose going to the pump (so coolant just before and after H/E) it looked normal. The coolant from the H/E itself was discolored. Like it had just become a problem. I would have expected, and can't figure out why it wasn't, that all of the coolant would be the same color. The engine was run a few days ago and the rust is probably from my trying to flush the manifold a month ago. I also found some sealant inside a pipe that was probably from its assembly who knows how many years ago, but I am sure it restricted flow somewhat. But all that was on the engine that is doing fine. The other one came out clean.
So today, day two, in the rain, I took it for a ride. Judging by the gages only it appears that it ran cooler by maybe five degrees, which was picked up by the other motor. So I would have to say that (the formerly) rust filled H/E (I did flush it out, remove the ring of sealant and scrub the tubes while I had it out) works slightly better than the other one, but the same engine still runs too hot, about 190 at 2900.
So, to recap: I don't think it is raw water flow (which includes the impeller, raw water pump, restrictions in the intake, etc.) because the volume is basically the same as the other engine and I don't think it is the H/E because I swapped them with very little difference. So the next step would be to replace the coolant pump? Do they ever go a little bad or do they just fail?
Still can't get new pictures to post.

KAG,

Below is the Help info for attaching files. Perhaps it will help you post some pictures. Size does matter!

Erich



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KAG, I was going to post a few images of the SBC circ pump interiors for you (shaft/bearing assembly/ceramic seal/impeller) but since there are so many arrangements, I decided not to confuse the issue here.

The Marine SBC uses the short body GM circ pump housing design from 1955. These were not ported for heater core coolant return until a few years later.
These use a steel impeller and do not hold up well under Raw Water cooled engine usage.
The Marine version circ pumps not only uses the bronze or SS impeller, but are also bi-directional.
(don't confuse bi-directional with reverse flow of the mid 90's automotive)

If the previous owner used the automotive pumps, and did not bother to change them when he installed the Closed Cooling systems, it could be that the impellers have become corroded and compromised in their ability to circulate coolant.

I'd remove them and remove the rear covers.
You'll be able to see what impeller material was used and/or the condition of the impellers.

For your LH Standard Rotation engine, you can use the less expensive automotive short body circ pump.
However, for your RH Reverse Rotation engine, you'll want the bi-directional Marine pump.

So, if you were to replace these, you're looking at about $30 for the LH engine, and about $70 for the RH engine.
If you replace these, they can be checked off of your P of E list.

.

Another sunrise trip to the boat, this time to pull the water pump (engine, not raw). It is a GM pump, #3839175, which seems pretty standard. The impeller is stamped GM 6269981 MB. The shaft appears to be ss and the impeller bronze with straight fins. Which, I think, makes it a marine, bi-directional pump (right?). There is no apparent physical damage and it spins freely. Other than out of desperate need to do something, I don't think it needs to be replaced, unless I am wrong and it is the wrong pump, in which case I would need some advice as to what to replace it with.
As far as I can tell, with the thermostat in, there is no circulation of coolant, at all, until the thermostat opens. There is circulation on my other motor, which has the same style housing. I assume, based upond comments above, but have not checked, that there are holes in that thermostat. I am going to try and get one with holes, or drill some in the existing one, unless advised to the contrary. I don't think this has anything to do with my problem but don't like the way the temp shoots up until the tstat opens.

I have not seen others, but mine came with three holes of about 5/16". Spaced equally on the vertical non moving part of the thermostat. I bought a replacement that had two holes, slightly bigger, so I don't think it is too critical.

CaboJohn

KAG, it sounds like the bronze straight fin impellers are correct for bi-directional useage.
If they are both tight to the shafts, and if not compromised, they should be OK.
However, if this pump is for the Rev RH rotation engine, the pump body (cast housing) must also be correct for reverse rotation.
You may want to compare your pump body to one that is known to be correct for Reverse Rotation.

Be sure to install new cover gaskets.

As for the thermostats, the small holes are air bleed holes. They aid in releaving a freshly filled system of air only.
You should not need to increase the size nor the amount of these air bleed holes. The single tiny air bleed hole should be sufficient.

Correct! There will be little to no coolant circulation until the thermostat begins to open.
The circ pump is continuously charging the engine block with coolant pressure..... (mild pressure, I may add).
Once the stat begins to open, we then see coolant leaving the block.... I.E., coolant flow.

Since the stat begins to open only upon sensing temperature, engine temps may increase rather quickly at first.
If temps taper off and hold within operating range, I'd consider this to be normal.


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there should be a minor bypass around the thermostat...the correct housing will have that port integrated within it. Drilling the t-stat is another way of getting the same function albeit not preferred. This bypass will provide a minor amount of circulation which may or may not be visible given your unique arrangement.

the circulating pump with the "straight" cast impeller will work rotating either way...you should be fine there.

A search in the internet looking at words such as bypass, cooling systems, thermostats, etc. will quickly convince you that all cooling systems (marine and automotive) seem to be designed with some form of bypass. A look at Crusader engine manuals will show a variety of solutions in the various models. In my case (5.7 Captain's Choice) I can tell you for sure that holes in the thermostat is the method selected by Crusader. You can order that thermostat pre-drilled from a variety of sources or drill the one you have. If you have some form of bypass already you don't need the holes (other than a recomended small one for air bleed that eases filling the system). If you do not have a bypass, I would try the holes. They were good enough for the (then) top of the line model.
CaboJohn

John, I'd have to say that an air bleed hole and a by-pass are not one in the same.
Some T-stat housing will incorporate a by-pass port.
Most all good marine thermostats should be equipped with the small air bleed hole.

In this stat, the air bleed hole has a small brass pin in it.
http://www.google.com/imgres?q=mari...nw=211&start=0&ndsp=8&ved=1t:429,r:0,s:0,i:72



In this T-stat housing, you can see the by-pass port.