454 antifreeze burn smell at start-up

[mcastellitto]

I have twin merc 454's FWC with 1010 hours on them. I've noticed the starboard engine let out an odor of antifreeze burning only at start-up after the engine sat for a while. The heat exchanger is remaining full but I do believe it is starting to draw from the overflow tank (I am watching that to verify). When will the system draw from the overflow, while running or afterwards when the pressure is gone? I have watched to see if I am getting any bubbles in the overflow tank and tube between the exchanger and overflow and I am not. The oil is clean and I am not overheating. The engine starts and runs great. To get that smell I would think the antifreeze is getting into the cylinders and combusting or in the exhuast (but would you smell it right away like I am if it is a leaking manifold or gasket?). Does anyone have any suggestions on where to start to look. Exhuast manifolds are 2 years old, gaskets look good and I don't see any sign of them failing. The smell is gone within 25 seconds of the engine running.

Any suggestions are appreciated.

 

[pdecat]

look at the plugs. any clean ones indicate water getting into the cylinder. other likely leaks are heat exchanger and oil cooler. Do a compression check while the plugs are out and also do a pressure test on the cooling system at the same time with the plugs out. It is good you detected the problem early and I suggest that you do the tests ASAP before trying to start the engine again to avoid fatal hydrolock if there is a problem.