Oil Sheen in Cooling Exhaust Discharge

[speedyfreak24]

Hi, I have a 1989 454 Mercruiser Stern drive w Bravo 1. Today I fired it up first time since layaway, where I properly winterized w RV antifreeze. Motor jumped to life as usual, and on water muffs, seems like I couldn't discern the pink antifreeze coming out of exhaust. Then around when up to temp and thermostat opened, discharge cooling water off back of transom looked brownish (never seen this before). I filled the bucket in pic with it and you can see the oily residue sheen on top. This cleared up after running at idle for 7 minutes and water had since been clear w no oily residue. I checked motor oil and there does not appear to be water intrusion, while boat seems to run cool and idles normal. I did a bit of carb fogging at lay-up, but am stumped and was looking to get on the lake in a few days. Any ideas would be greatly appreciated!

 

[tpenfield]

Hard to tell, because there could be a number of possibilities . . .

Based on what you described, there was probably some rust that remained in the engine block until the thermostat opened up ( IIRC, there is a 143˚ F T-stat in those engines, later became a 160˚ F as standard).

The oily sheen could be a cylinder not firing initially as the engine warmed up.

Those are all rose-colored glasses explanations . . .

Alternatively, it could be that you are getting some leakage at the exhaust manifolds or even at the intake manifold . I would pull the spark plugs after running at idle for a while (1-2 minutes) to see if you are getting water in the cylinders.

If all is good and the engine oil remains pure, the next step would be to take the boat to the lake and see if you are causing 'water pollution' out of the exhaust.

FWIW - I 'had' a 1991 454 Mercruiser where the valve guides rusted through on the cylinder heads and started putting water into the cylinders . . . which led to a hydro-lock . . . bye-bye engine Your engine is the Mark IV version of the GM 454, and I believe GM did a bit of redesign of the heads with the Gen 5 and Gen 6 versions.

 

[speedyfreak24]

Thanks, will do on pulling plugs, so water would show up on plug tips? Would engine oil be seeing into the intake or exhaust manifold, is that the idea of how it gets into the discharge cooling water? I guess I could also do compression tests on cylinders to look for faulty head gasket, but wouldn't I see water in the oil at some point?

 

[Scott Danforth]

check the engine oil cooler or the power steering cooler

 

[speedyfreak24]

Great call, I will!