Hello, I recently bought an '89 Ski Nautique with 351 PCM motor (512 hours). Long story short when I water tested the boat we overheated it because the raw water pump was installed incorrectly. I went ahead with the purchase because after the raw water pump was installed correctly the boat ran fine, although it stabilized around 170 (it should run max temp of 160 with a 143 thermostat). I assumed at the time it was most likely an air leak or failing impeller and wasn't a big deal.
The next time I had it out on the lake under load I had very weird fluctuations in temperature. It would stabilize between 170-180 and would sometimes slowly creep up to 190 or so and would come back down. Again, it should run 160 max. I also noticed the exhaust risers were getting hot, but I seemed to be getting good flow. I messed with it a bit, but was unable to pin down the issue. I was pretty frustrated to say the least.
I finally gave in and took it in the local inboard dealer. They tested the cooling system (RWP flow, checked for air leaks, etc) and couldn't find anything wrong. They finally decided to do a fluid combustion leak test by somehow plumbing up a "T" into the hose between the tstat and exhaust manifolds. Anyway, the test showed exhaust gas in the cooling system and their diagnosis is most likely a blown head gasket. He said the exhaust gas getting into the cooling system is causing it to run warm/hot and it's likely a small leak. The good news at this point is the compression is good (125+ in all 8 cylinders) and there is no water in the oil.
I'm just looking for a second opinion on this before I tear down the engine and get at the head gaskets. Do my symptoms sound like a bad head gasket? Is a fluid combustion leak test a pretty definitive test on a raw water cooled motor? I know it is on a car, just wondering if it would be as accurate on an engine that naturally mixes exhaust gas and water. Thanks for the feedback-
The next time I had it out on the lake under load I had very weird fluctuations in temperature. It would stabilize between 170-180 and would sometimes slowly creep up to 190 or so and would come back down. Again, it should run 160 max. I also noticed the exhaust risers were getting hot, but I seemed to be getting good flow. I messed with it a bit, but was unable to pin down the issue. I was pretty frustrated to say the least.
I finally gave in and took it in the local inboard dealer. They tested the cooling system (RWP flow, checked for air leaks, etc) and couldn't find anything wrong. They finally decided to do a fluid combustion leak test by somehow plumbing up a "T" into the hose between the tstat and exhaust manifolds. Anyway, the test showed exhaust gas in the cooling system and their diagnosis is most likely a blown head gasket. He said the exhaust gas getting into the cooling system is causing it to run warm/hot and it's likely a small leak. The good news at this point is the compression is good (125+ in all 8 cylinders) and there is no water in the oil.
I'm just looking for a second opinion on this before I tear down the engine and get at the head gaskets. Do my symptoms sound like a bad head gasket? Is a fluid combustion leak test a pretty definitive test on a raw water cooled motor? I know it is on a car, just wondering if it would be as accurate on an engine that naturally mixes exhaust gas and water. Thanks for the feedback-