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I have a 1976 bertram 31 and have Chevy 454 MerCrusier engines. I am having problems with it overheating at idle. The MerCrusier people have been out and cant seem to figure out why it is doing it. Has any one experieced this problem before?

Thanks

Take Time

If it's only at idle and OK under power and you (or Mercruiser) have checked your raw water impeller, check out your input hose to the raw water pump. Make sure the connection clamp is tight and/or the hose underneath it is not worn or deteriorated. I had a similar problem that drove me nuts and finally found that when not under power it was sucking a bit of air through a cracked hose, enough to limit the amount of cooling water getting to the engine at idle.

i had a problem with merc 350 mag circulating pump on engine.the impeller is pressed onto the shaft and had come loose sometimes it would cool fine then other times it would spin free and not circulate the water thnrough engine

I had the same situation a long time ago. A bitch to figure out because everything looks and acts fine when looking at it. I drilled into it between the vanes and installed a set-screw to resolve the situation. Never happened again.

Never had it happen to me but I have heard some of my mechanic friends talk about the Neoprene Impeller breaking its vulcanized bond to the drive hub.

From all outward appearances everything is fine but inside it no workey.

I cannot see how that would make an engine run hot at idle and fine at higher RPM.

If the situation were reversed (fine at idle and hot up and running) the problem would be easier to understand.

Interesting ! ! !

Harry

I can assuming the engine then runs okay at higher RPM's?

With a load or dockside?

Have the Risers, Oil Cooler, Tranny Cooler been checked for debris?

Sometimes you'll get a broken Impeller Vane, Barnicule, Rust Flake or whatever block a passageway and higher RPM's may allow water to move it or the flow goes around to make up the difference. Could a hose be collapsed?? Collapsed / restricted on the inside? Kinked where higher pressure allows it to un-kink? I've scene that recently on a tranny.

-Timing's been checked?

-Intake is open...good water flow?

-No leaks around pump....belts not slipping?

-Sure Key is in the Impellor?...

-Intake Hose have a pinhole, not clamped tight enough? Hose Old and hard losing a seal? Maybe it's pulling enough air at idle to make pump air-bound but at higher RPM's it become negligibly.

Let us know.

CArl

Raw water cooled or freshwater cooled?