cooling system/not the pump

[knot-a-clew]

"87 4HP Mariner. Engine pumps water when cold, but flow diminishes as engine heats up. When up to full operating temp., flow of water from "pee hole" becomes a mixture of spray and steam. If I shut the engine down, I hear the sound of air/steam leaking from someplace to somewhere as the pressure equalizes from higher to ambient. Once the sound stops (pressure equalizes) I can restart the engine and it will pump water for a minute or less, then the water flow diminishes all over again. No visable signs of a leak when I try to observe with the engine cowl off. What am I overlooking. Is there a pressure relief valve built into the cooling loop that is stuck closed, creating a back pressure on the water pump. That is exactly the way it acts. I have replaced the impeller, taken it apart to confirm that I did it properly the first time, reinstalled; cleaned the tube in the leg, run a wire through the outlet...just about everything I think of. Any ideas out there

 

[KCLOST]

Re: cooling system/not the pump

I don't think you have any pressure relief valve on that engine...<br /><br />Run a compression test on the cylinder.. It's possible the cylinder head gasket has failed, allowing exhaust to enter the cooling system... However I would expect that your engine would run rough or not at all when that happens... It's worth a shot to check it out...<br /><br />Here is a link to your schematics..<br /><br /> http://www.dougrussell.com/partscat...on=getcomp&colid=02&coldesc=4 H.P.&index=4603

 

[knot-a-clew]

Re: cooling system/not the pump

Originally posted by KCLOST:<br /> I don't think you have any pressure relief valve on that engine...<br /><br />Run a compression test on the cylinder.. It's possible the cylinder head gasket has failed, allowing exhaust to enter the cooling system... However I would expect that your engine would run rough or not at all when that happens... It's worth a shot to check it out...<br /><br />Here is a link to your schematics..<br /><br /> http://www.dougrussell.com/partscat...on=getcomp&colid=02&coldesc=4 H.P.&index=4603

 

[knot-a-clew]

Re: cooling system/not the pump

thanks for the quick response. Do you know what the compression should be???

 

[KCLOST]

Re: cooling system/not the pump

Man, that is a good question. I'm used to testing multiple cylinders and looking for consistency, not just a single one...<br /><br />Let's start at 100psi... Let us know what you find out... And we'll check into that for sure...