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The old 470 overheating problem

L

Larrykoch

New member
I have read many posts about overheating on a 470. Unfortunately that was after i purchased a boat that had a known overheating problem. The owner had also installed a 4 inch heat exchanger. Well anyway i found a leak in the input system from the sterndrive fixed that still an issue. Seems like I cant overheat in the driveway on a hose but in the water at high speed after several miles temp starts to climb and coolent is boiling in the overflow an leaking out to make the problem worse. Replaced the water pump just in case with OEM pump still problem no help. Replaced riser and exhaust manifold because manifold had a sealing problem where it meets the riser surface was all pitted and inserts put in by last owner and the problem got allot better but not cured. I had already changed the Thermostat. I just learned about cam shaft wear and leakage thru the weep hole checked and there is no fluid from there.
I am down to the head gasket. I tried some head gasket stop leak solutions with know success.
The question is, Is the head gasket the next logical choice?
Is there any other test I can do before I tear apart the top of this motor?
 
IF the head gasket is leaking exhaust into the heat exchanger, you will see the boiling coolant coming out in short order. Also, the temp has to rise since the coolant is being heated by exhaust gas (which also aerates the liquid, reducing cooling).

Time for a compression test to see if a cylinder is low.

Jeff
 
fastjeff said:
IF the head gasket is leaking exhaust into the heat exchanger, you will see the boiling coolant coming out in short order. Also, the temp has to rise since the coolant is being heated by exhaust gas (which also aerates the liquid, reducing cooling).

Time for a compression test to see if a cylinder is low.

Jeff
Click to expand...

Checked the compression with the engine cold
1. 152
2.145
3.145
4.140

I would say that is pretty good for a 30yr old engine. Not sure where to go from here?
 
one of the things that is strange is I can run it in the driveway for a long time and it has never got hot. If the head gets hot could it be flexing or moving?
 
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