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Old 09-01-2012, 15:38   #16
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Re: weird engine overheating problem ...

This is not specific to your engine, but has your themostat got a bleed hole in it? If not, drill a small hole in the flange of the thermostat so that a little coolant or trapped air can bleed past. This allows warm water to work its way up to the thermostat and lets it open.
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Old 09-01-2012, 15:45   #17
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Re: weird engine overheating problem ...

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Originally Posted by boden36 View Post
This is not specific to your engine, but has your themostat got a bleed hole in it? If not, drill a small hole in the flange of the thermostat so that a little coolant or trapped air can bleed past. This allows warm water to work its way up to the thermostat and lets it open.
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Yes it does. Thanks
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Old 09-01-2012, 16:29   #18
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Re: weird engine overheating problem ...

I'm sorry I missed the real info; what engine do you have?
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Old 09-01-2012, 17:10   #19
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Re: weird engine overheating problem ...

The coolant can only leave the block a number of ways. Being burned (head gasket, block, piston, head), being expelled (head gasket, defective hose/pump, overflow, heat exchanger/tube-stack). With the coolant warm to the touch and the engine over heating, I would say the coolant isn't making it's way though the system. This could be explained by a faulty FW pump/impeller, but not the coolant loss. What would stop it from circulating through the pump and create a loss of coolant? Tube-stack on the lower side. Check your mixing valve, it will be cool, as well as the exchanger. Your coolant's being flushed.
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Old 09-01-2012, 21:00   #20
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Re: weird engine overheating problem ...

Quote:
Originally Posted by Seahunter View Post
Tube-stack on the lower side. Check your mixing valve,
I'm not familiar with these terms in relation to marine motors. Can you elaborate.
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Old 09-01-2012, 21:21   #21
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Re: weird engine overheating problem ...

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Originally Posted by MarkSF View Post
That does remind me of a problem I had with a V12 Jaguar. The line to the coolant catch tank was kinked, so it worked as a one way valve. Coolant went to the catch tank on expansion, but didn't get sucked back on cool-down. The result is a cooling system that constantly has air in it.

As the line gets suction on it on during cool-down, it needs to be a re-inforced hose - but mostly you find some cheap silicone tubing installed.
I had a similar problem with my Yanmar. The pressure cap was leaking so when the engine got warm the coolant would leak past it...but because it didn't seal properly, the coolant never got sucked back when it cooled...clue was the overflow tank full of coolant....
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Old 09-01-2012, 21:30   #22
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Re: weird engine overheating problem ...

Here's one that happened to me in a fuel line. It was the devil to find. THe hose lining delaminated and sometimes sucked into the fluid path. It always looked fine when I pulled the system apart.

On another note, our seawater system gets shells, algae etc. THe first time I took it apart there were bits of Zincs broken off. I found that Clorox in the strainer once and a while is dynamite on the critters and totally removes algae & slime.
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Old 09-01-2012, 21:34   #23
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Re: weird engine overheating problem ...

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Originally Posted by Nicholson58 View Post
Here's one that happened to me in a fuel line. It was the devil to find. THe hose lining delaminated and sometimes sucked into the fluid path. It always looked fine when I pulled the system apart.
That was a common problem on older exhaust hoses where the heat hit the hose coming out of the exhaust elbow or at a tight bend.
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Old 10-01-2012, 05:46   #24
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Re: weird engine overheating problem ...

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Originally Posted by delmarrey View Post
I'm not familiar with these terms in relation to marine motors. Can you elaborate.
Mixing valve or exhaust elbow or riser all Googlable

Tube stack or heat exchanger tube stack or heat exchanger also Googlable.


Attachment 35811

"D" IS THE TUBE STACK


Attachment 35812


TUBE STACK OUT OF THE BOX


If raw water has been sitting in the lower end of the heat exchanger there's no doubt corrosion. Corrosion leads to failure and leaks.
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Old 10-01-2012, 05:50   #25
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Re: weird engine overheating problem ...

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Originally Posted by delmarrey View Post
That was a common problem on older exhaust hoses where the heat hit the hose coming out of the exhaust elbow or at a tight bend.
Exhaust elbow or riser fouling with carbon is a common source of engine overheat. They should be removed now and then and cleaned out or replaced. This happens usually because the engines not heating up sufficiently or something wrong with the fuel system.
This would NOT account for the coolant loss.
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Old 10-01-2012, 09:10   #26
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Re: weird engine overheating problem ...

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Originally Posted by sneuman View Post
Haven't changed the pump yet, but I think that's next on my list.

If it is a leak in the head gasket, we're talking big $$$, I assume.

Not really if you do the labor yourself. Just lots of labor unfortunately compared to replacing a pump.
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Old 10-01-2012, 10:05   #27
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Re: weird engine overheating problem ...

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Originally Posted by sneuman View Post
I have been fighting this one for awhile. No, it's not the raw water system (and therefore not the impeller) -- spew raw water like a champ. No, it's not the thermostat (replaced).

Here's what happens. I make sure the coolant is topped off (including "back filling" to the circulator pump to make sure there's no air lock). It appears to run fine indefinitely, but once it's shut down and restarted, the coolant stops circulating and it overheats fairly quickly. I know the circulation is the problem, because I can stick my finger in the coolant in the heat exchanger once it overheats and it's cool.

So, apparently a vapor lock forms after the engine has been run hot and shut down and then that prevents the coolant from circulating on re-start and causes an overheating situation.

Although I have been unable to locate any coolant leaks during a cursory inspection, my theory goes that there's a leak that releases just enough coolant when the thing is running to cause an air-lock on restart.

Does this sound at all plausible?
One of the keys to this puzzle is that the cooling system works fine until you shut the engine down and restart. Did you let things cool off, or did you restart it warm?? When you said you stuck your finger in the HX coolant and it's cool, was it cold or warm to the touch, and how full was the coolant when you took off the cap? How do you know the engine is overheating?

You might have circulating pump with an intermittent failure, a blockage in the system (Like the thermostat), or a leak in the freshwater side (if you don't see any leakage it could be a head gasket or the HX tubing). You also might have a bad temperature sender. I would

1. Replace the circulating pump (you have a spare)
2. remove the thermostat
3. Pressure test the system (for ideas, see

Make an Auto Radiator Pressure Tester

4. Borrow or buy an infrared temperature gun (at Sears for $30)
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Old 10-01-2012, 10:23   #28
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Re: weird engine overheating problem ...

Quote:
Originally Posted by Seahunter View Post
Mixing valve or exhaust elbow or riser all Googlable

Tube stack or heat exchanger tube stack or heat exchanger also Googlable.


Attachment 35811

"D" IS THE TUBE STACK


Attachment 35812


TUBE STACK OUT OF THE BOX


If raw water has been sitting in the lower end of the heat exchanger there's no doubt corrosion. Corrosion leads to failure and leaks.
Please confirm that you meant mixing elbow when you said mixing valve--the OP's problem is with his engine, not his shower.
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Old 10-01-2012, 10:55   #29
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Re: weird engine overheating problem ...

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Originally Posted by donradcliffe View Post
Please confirm that you meant mixing elbow when you said mixing valve--the OP's problem is with his engine, not his shower.
I also stated, exhaust elbow and riser; but yes "mixing elbow" can be thrown into the mix. However, I doubt if this is the problem. The more I think of his description makes me think that his tubestack has failed. It's probably plugged up so bad that raw water can hardly pass. The only water exhausted is from the bypass to the riser and is pumped overboard (making it appear as if water is getting through the heat exchanger), while the engine over heats, the coolant pressure rises, squirting out pinholes in the lower tubestack and out the exhaust. This would account for the coolant loss, as well as the overheat. One could pinch off the bypass to riser hose with a pair of vice grips and see if any raw water is making it through the tubestack. You'd have to be quick so as not to damage the exhaust system with overheated gases.
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Old 10-01-2012, 11:03   #30
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Re: weird engine overheating problem ...

It's an Isuzu Pisces. A marinized forklift engine - 4cyl, 55hp.
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