Volvo Penta 8.1Gi-G Persistent Overheating Problems

[Jack D]

I have a Volvo Penta 8.1Gi-G with a 290DP leg on my boat. Engine is 2006 vintage with about 300 total hours whereas the leg is the original 1994 vintage with about 1300 hours Engine is overheating (210 - 215F)despite recent maintenance done to solve the problem which included new exhaust manifolds, risers and complete new raw water pump. Heat exchanger cleaned and thermostat changed. After the maintenance, on the first water run, engine temp cycled quickly (1 minute) from 175 F to 210F then back to 175 (when under mid range load at approx. 3100 rpm). Engine temp stayed down at around 180F when at idle.

After shutting engine off for a few hours to do some fishing, on start up the engine temp then operated differently - rising to 210F and staying there when running at 3100 rpm for trip back to marina. Since I've owned the boat (8 months) I have never been able to keep antifreeze in the expansion tank although it is not clear where it goes. Mechanic pressure tested the closed cooling system (from the expansion tank filler) and indicated it was OK. Pressure test was done cold so with a closed thermostat.

Any ideas? I was wondering how one determines if there is enough antifreeze in the engine? I had assumed since I lose the level in the expansion tank that it is boiling off from overheat although I've only once observed a bit of green in the bilge (which could have been from the last filling). I am assuming that if the engine is overheating, if adequate antifreeze in the engine, then the expansion tank should be full to overflowing when checked with hot engine but this is not my case.

 

[Scott Danforth]

Check the inlet hose between the transom shield and out drive, specifically the little casting on the drive side.

Are you running an expansion tank? If your loosing coolant, you have a breach somewhere. Pressure test the system.

 

[Jack D]

Yes, there is an expansion tank and during the recent maintenance the closed cooling system was checked by a Volvo Penta mechanic and found to be OK. Pressure pump/gauge was applied to the cap on the expansion tank with the engine cold. One of the concerns I had was whether this was a legitimate pressure test of the complete cooling system or would the closed thermostat suggest only a partial test?? The other concern I had (since there was no indication in the bilge of overflowed coolant, is there a possibility that there is insufficient coolant in the engine so what I add to the expansion tank is simply being drawn into the engine.