Blocked cooling passages????

[kazdeb]

I have a 1986 Chris Craft sterndrive with the Mercruiser 3.0l ,140 hp engine. It was running fine until some preventative maintenance was performed. Opened the cooling system to replace thermostat. Found it in pieces. Retrieved as many as I could find.. Removed the intake/exhaust manifold and end plates looking for any other pieces. Reassembled all parts. When engine was running on muffs, was not getting same amount of flow through the prop. Took it to the lake for testing, and the engine was running at 210 degrees at slow speeds. Slowly motored back to the dock and hauled out. I am thinking that some parts of thermostat circulated into the block, thus causing the reduced flow at the prop. Any help and suggestions would be greatly appreciated.

 

[cowboykid8]

Do you still have the pieces of the thermostat? Figuring out how big of a piece you are looking for will help you diagnose where it may be lodged. Also use the cooling system diagram to find likely spots.

I have had success reversing the flow with a garden hose. Also trying to shopvac the water and piece out.

 

[Rick Stephens]

If having temperature issues, always inspect the impeller. Might not be the problem but surely can cause em.

 

[thumpar]

Are you sure it was the thermostat in pieces and not the impeller? It is normal to not get water or very little water thru the prop on muffs. It all comes out the relief ports. Does the gauge actually show 210 or is that a guestimate? My only thinking is that the impeller went and got all over. You cleaned and replaced it and everything is fine with the gauge but you are watching it a little closer than you used to now. When my impeller went I just backflushed it with the hose to get things cleaned out. I was very cautious though and anything close to above 175 started to bother me. After running a full summer since then I don't get so worried anymore.

 

[Bondo]

If having temperature issues, always inspect the impeller. Might not be the problem but surely can cause em.

Ayuh,... Ditto that,.... In most any overheat situation, the Impeller is the 1st place to look for the problem,....

 

[stonyloam]

Yeah thermostats do not just fall apart, if the pieces are rubber, they are what is left of a disintegrated impeller and you are no longer pumping water to the engine, bondo and thumpar are right (again) that is the cause of the overheat.