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Rebuilt Mercruiser 5.7 Running HOT!?

S

Scott Mosteller

Member
Hey friends! I am new here and wanted to see if you guys could help me out!

I just rebuilt my chevy 350 last year, she has about 10 hrs on it. Right when I rebuilt it, the alpha 1 drive blew up as well. SO, i put her in storage for 6 months and just waited till i had the funds and time to fix her. Finally, i got a new drive put on, and shes ready to romp!

I just installed a new temp gauge tonight, (didn't have one before) and when i backed her into the water at the launch ramp, i just left it attached to the truck. I jumped in and wanted to run it and see what she was doing. After 10 minutes or so, the temp gauge is reading 210 degrees at idle... a little high!!

I checked the left exhaust riser and its real hot, the right one is semi hot. It is raw water cooled for the exhaust, and i have a heat exchanger for the engine cooling system. The heat exchanger is ALSO hot, REALLY hot. I just replaced the raw water impeller as well. So strange, the raw water inlet hose that connects to the impeller housing, was REALLY pinched, like real bad. I gassed it hard twice and im not sure what happened, but it fixed the hose and i think its flowing well again? something seems clogged or pinched cause its still hot and im lost for words right now.

I replaced everything when i did the engine rebuild. Water pump, exhaust headers, risers, etc. I didn't replace the heat exchanger though, do we think that this may be the problem? Maybe get it hot tanked or something?

Happy to answer any questions to help me get to the bottom of this! Shes so close i just need to finish up some of the kinks and she'll be rip rap!

Thanks friends, scott!
 
What thermostat is in the motor?

Typically all closed cooling systems as yours should be running a 160* thermostat.
If you do not have this temp stat then replace it!!!

The pinched water hose is typicall of a aftermarket hose installation. The aftermarket hose is not as rigid as a OEM
Also if it was not installed correctly this can occur.......meaning all the way onto the transom water tube.....
This will cause a over heat issue for sure!!

Only problem is once kinked it will kink again

If you trim the drive out a couple of inches this should releave the kink and allow full water flow. (not a fix but a work around until the hose is fixed or replaced)
 
OK. First all Alpha drives running heat exchangers except for the 3.7 must convert to a belt driven water pump and a thru hull fitting. There is a Bulletin from Mercruiser on this along with all the part numbers needed.


Second. You should never just change an impeller on an Alpha drive. You should change the whole pump including the base. If the base is out of shape slightly it will pump air into the engine and cause an overheat. Mercruiser parts only on this.

Third. My opinion, if you have a clean heat exchanger and a good water pump along with a clear exhaust, you do not need a belt driven raw water pump unless you are running for a few hours non stop not allowing the engine to cool.
 
Scott, you have what's called a "half" closed cooling system, meaning that only the engine block/cylinder heads are in the closed system loop and that the exhaust manifolds remain seawater cooled.
Elbows are always seawater cooled whether open or closed system.

Chris makes a good point. The A drive seawater pump is sometimes incapable of supplying enough seawater to remove the engine heat.
Although.... I have also seen many of these where they work just fine for a half system.
Nonetheless, perhaps replace the entire pump.


As for the H/E..... you may want to have it serviced. Rust scale can build up around the tube bundle on the E/G side of the system. As it does, the tube bundle becomes less efficient at removing heat from the ethylene glycol.
You'll have a finite amount of seawater to remove the heat from the Ethylene Glycol. When/if the tube bundle does not function correctly, no change to the thermostat is going to make much difference.

BTW.... the E/G side of the tube bundle is not easily accessable by average Joe. The seawater side of the tube bundle is accessable.


As for one side being hotter than the other...... look at the where the "spent" seawater is divided (spent seawater = what leaves the H/E).
If this is not being divided equally, one side will run hotter than the other.
Some temperature differential is acceptable... but it should be within reason.



.
 
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WOW this forum kicks A**! I will replace the thermostat again ASAP. I'm not what i replaced it with before, but it may be a little higher - either way, better safe than sorry!

The pinched water hose issue - it is an aftermarket hose - and I have more that i can replace it with to give it back the rigid state it used to have. It IS installed ont he transom water tube all the way for sure, and def not leaking, checked that multiple times.
 
I really never run the engine more than 30 minutes without either taking a break for a few minutes, or stopping and fishing for a couple hours. Shes an old boat haha not trying to break her but i do want to travel the fishing grounds and not get stranded, again!

I dont have a belt driven water pump, its all just suction from the outdrive. I replaced the raw water impeller thats connected to the harmonic balancer area i believe. I am not sure if the heat exchanger is clean or not, it looks like it could use some help. I know it has 2 bolts on the side so i may try to take those off tonight and see if i can clean it myself without taking it to some radiator shop. Any thoughts on that?
 
First off, again thanks for everyones input, this is HUGE for me!!! Since this is a 'half closed system', i think i have the pieces and parts in place in order to make it successful. I just need to do some work to ensure its not overheating!!

Makes sense on why one side is hotter than the other. SO im hoping its a variety of smaller things leading to the heat issue. SO!!!!

Action list:

Replace thermostat with 160
Replace lower pinched hose with newer aftermarket application
Take apart heat exchanger and clean with break cleaner and heavy brushes

Any other suggestions? Thanks friends for all your help!

If anyone is in San Diego, my boat is open to all of you for a put around the bay. Lets drink beer, jam to good tunes and do some fishing :)

Cheers!
 
Scott Mosteller said:
I really never run the engine more than 30 minutes without either taking a break for a few minutes, or stopping and fishing for a couple hours. Shes an old boat haha not trying to break her but i do want to travel the fishing grounds and not get stranded, again!

I dont have a belt driven water pump, its all just suction from the outdrive. I replaced the raw water impeller thats connected to the harmonic balancer area i believe. I am not sure if the heat exchanger is clean or not, it looks like it could use some help. I know it has 2 bolts on the side so i may try to take those off tonight and see if i can clean it myself without taking it to some radiator shop. Any thoughts on that?
Click to expand...


Is this a Volvo Penta or a Mercruiser with an Alpha drive?
 
Docksidemarineservices said:
Is this a Volvo Penta or a Mercruiser with an Alpha drive?
Click to expand...

It is a Mercruiser with Alpha drive. 1979 boat with a whole mess of new parts from the previous owner and myself. I took some pics tonight to show you guys what i am working with. I replaced the thermostat today with a 160 degree and fail safe (The $14 one with a new gasket). Took the boat to the launch ramp tonight and backed her up. Ran it for 15 minutes again, giving it throttle every so often to bump up the temps. It ran around 190-200, but didn't hit 210 like it did before, so maybe that helped a little bit?

The hoses were not pinched so thats a plus, and i think i felt water flowing through the raw water. BUT, the top of the exhaust risers were still hot, and the heat exchanger was VERY hot to touch, still. I am thinking next i need to take the heat exchanger off and send it over to a radiator shop to get it hot tanked and cleaned up real good. Then top her back off with coolant and try again?

Any other thoughts? Thanks guys, i really appreciate it!

https://www.dropbox.com/s/fnmpe7tja55w2r5/1.JPG
https://www.dropbox.com/s/g6rlep162mig8vd/2.JPG
https://www.dropbox.com/s/cg8i7m7xfy3ie5k/3.JPG
 
"I replaced the raw water impeller that's connected to the harmonic balancer area"

Can you explain this?


Get an IR thermometer gun and check your engine temperature.



And remove the plastic fuel filter attached to the feed of the carb. Dangerous.
 
Docksidemarineservices said:
"I replaced the raw water impeller that's connected to the harmonic balancer area"

1..... Can you explain this?

2..... And remove the plastic fuel filter attached to the feed of the carb. Dangerous.
Click to expand...

1..... Chris, over the years I have installed the Johnson crankshaft pump on Mercruiser engines.
That is likely what he's refering to.

jp1451_l.jpg

NOTE:
The large Jabsco pump impeller measures 1.990" in depth.
The Johnson F5B-9 pump impeller measures 1.900" in depth.

Both look identical. Same diameter, same vane count, same splines, but the depth is different by .090".
If the F5B-9 impeller is installed in the Jabsco pump body...... you will have a problem.


2...... Yes... please remove that! These are not legal and it poses a risk.



.
 
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RicardoMarine said:
1..... Chris, over the years I have installed the Johnson crankshaft pump on Mercruiser engines.
That is likely what he's refering to.

jp1451_l.jpg

NOTE:
The large Jabsco pump impeller measures 1.990" in depth.
The Johnson F5B-9 pump impeller measures 1.900" in depth.

Both look identical. Same diameter, same vane count, same splines, but the depth is different by .090".
If the F5B-9 impeller is installed in the Jabsco pump body...... you will have a problem.


2...... Yes... please remove that! These are not legal and it poses a risk.



.
Click to expand...
I do not assume that he has this pump set up.
 
It is fairly close to the set up above, not sure exactly what it is though. I feel like the pump is ok as is with the new impeller, no blockage or leaking coming from that section. I DO think i have a blockage somewhere else though, do we think its in the heat exchanger?

I will remove the fuel filter, sorry i had no idea!

Thanks
 
Scott Mosteller said:
It is fairly close to the set up above, not sure exactly what it is though. I feel like the pump is ok as is with the new impeller, no blockage or leaking coming from that section. I DO think i have a blockage somewhere else though, do we think its in the heat exchanger?

I will remove the fuel filter, sorry i had no idea!

Thanks
Click to expand...

So, you have a hose connected to a thru-hull fitting on the bottom of the boat?
 
RicardoMarine said:
Scott, if you do have the old Jabsco crankshaft pump, it will look like this one.
Note the large base housing that requires the longer mounting bolts, and the six cover screws.

284899=6119-pump%20apart2.JPG
Click to expand...


Yup looks similar to that but not exact of course. I just got a new impeller for the pump so it seems to be working correctly. Going to take the heat exchanger off next and get it all cleaned up at the radiator shop.

I have 2 thru hull fittings for the boat. But both are not for the engine. 1 for the bait tank, and 1 for the raw water wash down pump (hose hookup).

Thanks guys!
 
RicardoMarine said:
Scott, I'm with Chris........ where is the crankshaft pump pulling seawater from?????? Please ...., not from the A drive!!!!!!
Click to expand...

Hey there, YES it is pulling sea water from the drive, an inlet at the bottom of the drive of course. Should I be pulling sea water through a thru hull fitting or something? I dont have it configured like that as of right now, but id be happy to switch it over to make all my problems go away!!!

I pulled the heat exchanger, got it flushed and cleaned ($100 job) put it back on the boat and of course, its still hot!!!!! The starboard exhaust riser manifold is still a little hot, and the right semi-hot. But the heat exchanger, too hot too touch after 10 minutes of running sitting on the dock. Engine is running around 190-195 consistently based on the gauge i got.

ALSO - i have the pinched hose problem again! Right before the raw water impeller coming off the crank shaft, its sucking so hard from the impeller that its literally compressing and pinching 2 hoses coming from the drive. I DONT GET IT! WHY is it pinched? Not sucking enough water?

I like the idea of a thru-hull fitting going directly to the impeller... is this a real thing? Should i modify it so i dont have this overheating / pinching problem? I JUST got the drive serviced and its practically brand new. So not sure what the problem is at this point.

IDEAS?
 
A typical motor mounted water pump impeller system the water pick up is thru hull.

The hose used on between the thru hull pick up to impeller is a rigid reinforced hose. (so it wont collaspe under high vacuum)

If you are useing the wrong type hose that may be an issue.

Maybe chris can comment on your set more specifically. I do not have a great deal of experience with your set up.

What I will suggest is IF your boat has been in salt water for many years as a closed cooling system suggests, the elbows may be clogged due to corrosion......

Keep in mind there are typically three issues with over heating

1. Water coming in (lack of or ubstruction)

2. thremostat (not working properly, wrong set point, obstruction)

3.water going out, (clogged exhaust elbow in your case due to closed cooling or both the manifold and elbow on raw water cooled)
 
Again, with all due respect!

kghost said:
A typical motor mounted water pump impeller system the water pick up is thru hull.
In many I/B scenarios, yes I agree........ but don't forget about the Volvo Penta I/O's with crankshaft pumps. These pull seawater in through the drive.

The hose used on between the thru hull pick up to impeller is a rigid reinforced hose. (so it wont collaspe under high vacuum)
Agree.... the suction hose must be collapse proof.
BTW..... Volvo Penta uses a heavy wall non-wire reinforced suction hose, and has for years. No issues that I'm aware of.

If you are useing the wrong type hose that may be an issue.
I fully agree.

Maybe chris can comment on your set more specifically. I do not have a great deal of experience with your set up.

What I will suggest is IF your boat has been in salt water for many years as a closed cooling system suggests, the elbows may be clogged due to corrosion......
Yes, certainly a place to look.
If the "spent" seawater cannot easily pass through the elbow's mixing chamber, it sees this as a restriction.

Keep in mind there are typically three issues with over heating

1. Water coming in (lack of or ubstruction)

2. thremostat (not working properly, wrong set point, obstruction)

3. water going out, (clogged exhaust elbow in your case due to closed cooling or both the manifold and elbow on raw water cooled)

4. And/or a Heat Exchanger tube bundle that needs attention at either the seawater side and/or at the ethylene glycol side, or both.
Click to expand...




.
 
A typical motor mounted water pump impeller system the water pick up is thru hull.


In many I/B scenarios, yes I agree........ but don't forget about the Volvo Penta I/O's with crankshaft pumps. These pull seawater in through the drive.

Rick

This is a mercruiser forum NOT volvo penta..............PERIOD

No one cares what volvo penta uses..................the reason, Merc does not use it............the result.........NO ADDED VALUE TO SAY IT.

You can't keep comparing what volvo penta does or does not do VS Mercruiser when answering questions.

It only confuses the person looking for answers..............
 
You guys are awesome. So whats been replaced recently and has less than 10 hours on is:

Exhaust manifolds
exhaust risers
thermostat 160 - with fail safe
raw water impeller
harmonic balancer
belts
starter
all hoses

So... from what im hearing, sounds like i may have the wrong hose!! it is radiator hose. I literally took the old hoses that were on the boat, and went to pep boys and matched up all the pieces. i didn't know they were supposed to be something stronger than radiator hose so thats my fault.

So maybe i am getting good enough suction and water from the outdrive? And the hoses are collapsing and not getting enough waterflow? causing it to overheat?

Man i hope so!!!! Going tom to get some new hoses! So it goes directly from the oil cooler to the raw water impeller inlet, anything else i should know about this?

Thanks so much guys, you are truly awesome helping me out! I just want to go to coronado islands from san diego bay and not break down! i'll take anyone who is ever down this way once shes all fixed up :)
 
Scott, I just now looked at your photos.

I don't quite understand why a person would use the AQ series Volvo Penta exhaust on this Merc installation.

I can't quite see the 90* exhaust manifold inlet fittings. Are these Marine grade... meaning NOT the average Hardware store type?

Also, is your ignition system Marine or Automotive?

As for hoses.... the corrigated hose running from the crankshaft pump to the H/E inlet port need not be collapse proof.
I'd loose that corrigated hose and would replace with an auto parts hose with the correct bends in it.... and you can find one if you look long and hard enough.


BTW... there's nothing wrong with your installation as long as the 95mm Volvo Penta exhaust system connects to the Merc exhaust Y-pipe properly. I'll assume that elbow fittings were used there..... yes/no?

Also, the crankshaft seawater pump would be prefered, IMO.
These allow for easy impeller access, and there is no side load torque against the crankshaft pump bearings. IOW, they'll go for years and years before needing bearing/seal service.


Here are a few of my observations, if I may.
 

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Scott,

Stop wasting your time trying to get your system to work through the drive. It will never work correctly. Pull the boat, drill a hole and put in a fitting with a seacock. Your problem will then disappear. The current configuration will not work no matter what hose you install.

Simple explanation, your pump has a 1" or 1 1/4" hose on it, the alpha pump has just under a .5" water passage.

This is a must!


After you install the through hull fitting, replace the water pump in the lower unit, you can attach the water feed hose from the drive in the bilge through the transom and make a drive shower, or put a plug in the water hose inside the boat hull and cut the water line in the transom assembly. Either one will keep the drive cool.
 
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Docksidemarineservices said:
Scott, Stop wasting your time trying to get your system to work through the drive. It will never work correctly. Pull the boat, drill a hole and put in a fitting with a seacock. Your problem will then disappear.
Click to expand...
Scott, I agree with Chris. The A drive seawater passages are small, and are designed to work under pump pressure (seawater pump in drive), not under suction (engine located seawater pump)!

However, keep in mind that the A drive seawater pump must be maintained in order to provide upper gear box cooling.
This water can be either diverted overboard, or it can join the cranksahft pump's suction system.
 

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RicardoMarine said:
Scott, I just now looked at your photos.

I don't quite understand why a person would use the AQ series Volvo Penta exhaust on this Merc installation.

I can't quite see the 90* exhaust manifold inlet fittings. Are these Marine grade... meaning NOT the average Hardware store type?

Also, is your ignition system Marine or Automotive?

As for hoses.... the corrigated hose running from the crankshaft pump to the H/E inlet port need not be collapse proof.
I'd loose that corrigated hose and would replace with an auto parts hose with the correct bends in it.... and you can find one if you look long and hard enough.


BTW... there's nothing wrong with your installation as long as the 95mm Volvo Penta exhaust system connects to the Merc exhaust Y-pipe properly. I'll assume that elbow fittings were used there..... yes/no?

Also, the crankshaft seawater pump would be prefered, IMO.
These allow for easy impeller access, and there is no side load torque against the crankshaft pump bearings. IOW, they'll go for years and years before needing bearing/seal service.


Here are a few of my observations, if I may.
Click to expand...

THANKS again guys, so awesome. Im not sure why they did it that way, but the exhaust system does work and connects to the Y-pipe in the back with zero leaks. YES i am using elbows coming off the risers and into the Y-pipe as well.

They are marine grade, they are brass and got them at a local hardware marine store.

The ignition system, DEF automotive, again, hacked together :-( but it works, any downfalls to having that?

The corrigated hose isn't collapse proof, but its also BLOWING water since it is after the pump... does it still matter to get a different one and replace it?

Thanks for your thoughts, going through one at a time :)
 
Docksidemarineservices said:
Scott,

Stop wasting your time trying to get your system to work through the drive. It will never work correctly. Pull the boat, drill a hole and put in a fitting with a seacock. Your problem will then disappear. The current configuration will not work no matter what hose you install.

Simple explanation, your pump has a 1" or 1 1/4" hose on it, the alpha pump has just under a .5" water passage.

This is a must!


After you install the through hull fitting, replace the water pump in the lower unit, you can attach the water feed hose from the drive in the bilge through the transom and make a drive shower, or put a plug in the water hose inside the boat hull and cut the water line in the transom assembly. Either one will keep the drive cool.
Click to expand...

I am seeing that the pump inlet has a .5" hose from the water passage and curves around the engine into the oil cooler. So i have no problem with making a thru-hull fitting on this, just need a little more guidance thats all.

I want to take a new thru-hull fitting with a seacock, and go directly up to the raw water impeller pump inlet.

Here is what i am thinking: http://i.imgur.com/1trlnd8.jpg

How does that look?

Thanks!
 
RicardoMarine said:
Scott, I agree with Chris. The A drive seawater passages are small, and are designed to work under pump pressure (seawater pump in drive), not under suction (engine located seawater pump)!

However, keep in mind that the A drive seawater pump must be maintained in order to provide upper gear box cooling.
This water can be either diverted overboard, or it can join the cranksahft pump's suction system.
Click to expand...

YUP, seeing this is too small and not efficient enough for cooling the entire system. Does the drive need its own pump? or can it be eliminated completely and just use the raw water pump to cool the engine? OR should the raw water pump be split so it pulls water from the drive AND the thru-hull?
 
Scott, I like your drawing but there is an error in it. I'll mark it up and will post it in a while.

BTW, how you're supplying the power assist steering oil cooler looks great! That kills two birds with one stone.

As for the automotive ignition system, this poses two problems:

..... It's not USCG approved for an enclosed gasoline engine bay.
..... The advance curve will be incorrect for marine engine loads....... and is risky at best!!!!


.
 
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