4.3 merc water in oil

I have a 1992 4.3L mercruiser. The engine has a closed loop/fresh water cooling system. I found water in the oil (milky + quite a bit of clear non-mixed water). I changed the oil, filters, and plugs (tips were rusty). The engine turns over, but I haven't fired it up out of fear that I may cause further damage.
My theory: cracked exhaust manifolds resulting from lack of proper winterization. I suspect one or both manifolds were cracked when I last put water through the seawater side (on muffs). I don't suspect a cracked block since there has been no change in the closed loop coolant level, no water in the bilge, etc..
Any advice would be greatly appreciated -- thanks.

Re: 4.3 merc water in oil

Any advice would be greatly appreciated -

Click to expand...

Ayuh,... Welcome Aboard,...

I guess I'd light it up, 'n run it abit, as you've changed the oil....
Just to see that it runs,..

Then pull off the manifolds, 'n see what's up...

Re: 4.3 merc water in oil

ya sounds like manifolds are gone. there probly original which are 20yo and need replacing either that or you ingested it on your last run. while you have the manifolds off look to see if your water shutter is still intact but ya test it and see what happens.

Ryan

Re: 4.3 merc water in oil

Thanks for the advice! I appreciate the experienced second opinion(s). Guess I need to quit looking at it and go start it... Will post again with the results.

Re: 4.3 merc water in oil

Is it possible rain water got in?
You need to flush the motor out good or you will still get the white slush in the oil. I changed the oil three times plus the oil filter and still the white. I searched around the net and found using diesel fuel and diesel oil mixed to flush the engine. Take a real close look for cracks first before starting. You will see a bulge.
I had a 185hp straight Mercruser and left the top lid up to air out, forgot about it and it just poured that night and water got into the engine. Stupid design rocker cover oil cap. It had sat that summer.

Re: 4.3 merc water in oil

I have the same motor except a '93. I bought it from a couple that were selling it as is because there was water in the oil.. being a good mechanic of cars I thought I would give this a shot to get it started and enjoy the boat..

The first thing I noticed was that one of the exhaust manifolds were completely rusted out and they had pulled all the sparkplugs out of the motor; looks like they had been out of the motor for a while. I have a new one on the way. I am thinking the water got into the motor either by the manifold or because they left the plugs out for a while. Good reasoning?

I am going to change all the fluids to fresh stuff and I already replaced the impeller. Hopefully going to start it this weekend.

Where is the water shutter located? I am going to replace that while I am replacing the manifold...