488 mercruiser cooling problem

[jerrysmalley]

I have a 488 1983 with a cooling problem. I have replaced the impeller in the out drive and have had the engine water pump and heat exchanger checked by a marine mechanic. The engine runs at temp(140) until you bring it down off of cruise rpm to idle and then the temp climbs. It seems I am also loosing coolant slowly. Has a new riser and a 22 year old exhaust manafold. I am seeing steam in the water at the outdrive which is a new symptom.

 

[maverick325]

Re: 488 mercruiser cooling problem

1.Look for a blockage in the cooling line. 2 The hose where the bellows are might be cracked or blocked if you have steam sounds like you don't have enough water flowing into the risers to coole the gases down. Idle will give you much less water flow and pressure.

 

[jerrysmalley]

Re: 488 mercruiser cooling problem

Which line the sea water or coolant?

 

[maverick325]

Re: 488 mercruiser cooling problem

Sea water line.

 

[jerrysmalley]

Re: 488 mercruiser cooling problem

Ok, I have made sure the coolant is full and the engine ran without overheating at cruise or when droped down to idle. The coolant level held during the test run but the next day it was down about 1 inch. I suspect a cracked manifold or a broken gasket somewhere. There is no coolant in the bilge so it must be going out the exhaust. Compression checks out and the engine runs ok.

 

[jerrysmalley]

Re: 488 mercruiser cooling problem

How do I test for a coolant leak and how do I dertemine where it is?