mercruiser 470- runs good, but getting lots of water in the oil

[olazabel]

I have a 1978 mercruiser 470. It seems to run fine, but checked the oil today and it looked like a milkshake and level was WAY too high. We've only had it out once this year, and it ran fine. Temp is good, coolant is still full, I'm thinking it must be water that got in the oil somehow, but I'm not sure how. I didn't think there was any way for lake water to get into the 470 engine, but I guess I'm wrong. Where should I start looking?..... any help troubleshooting this would be much appreciated.

 

[Scott Danforth]

Two common 470 problems. Head gasket and exhaust manifold failure

 

[stonyloam]

Are you sure it is lake water and not antifreeze smell it to make sure. Yeah there is almost no way the raw water could get in there. The only contact raw water has with the system is where it exits into the exhaust elbow. There is no way that it should be able flow back into the engine.

 

[olazabel]

Didn't smell it, but checked the anti-freeze and it was full, so figured it had to be water. I'm pumping the oily milkshake mess out right now with a really slow electric pump. I'll check the antifreeze level again, smell the oil, and let you know.

 

[2fishy4u]

Exhaust manifold with a failed riser should be the only places for fresh water to enter the block.......

 

[olazabel]

Stony- I don't smell any antifreeze in the oil, and there were at least a couple gallons of extra fluid in the oil when I pumped it out.

I did have to add some antifreeze this spring when I took the boat out of storage, but it is still full now, after running for a few hours on the lake and looks clean.

I'm going to put fresh oil in it in the morning, run it on muffs for a while and see what happens.

 

[olazabel]

fishy- when you say "failed riser" do you mean the gasket?

 

[stonyloam]

Yeah the gasket on the exhaust elbow. If that were to fail you would loose antifreeze not raw water. Couple of gallons?? I think the cooling system only holds about 11 quarts, that's crazy. Yeah, I guess, just run it for a while a while and see if the oil stays clean.

 

[olazabel]

fresh oil and filter, ran it on muffs for a while (20-30 mins), seemed to run fine, oil stayed clean so I thought maybe the water got in there in some freakish way and I was good. ventured out to the lake, fired up fine, but when I engaged the prop the engine stalled every time.

oil still looks ok, but it hasn't been driven under load, mainly just idled in the driveway

I'm now thinking I might have a real issue. any suggestions on how to proceed?

 

[nola mike]

Engine stalling sounds like your shift interrupt, unrelated to your other problem. Next time on the water when it stalls see if the switch is tripping when you shift.

 

[2fishy4u]

My riser failed, rusted on the instide.Created a small hole allowing fresh water to blow back into cylinder 1. And make a nice milkshake out of my oil. Also, if your exhaust flap is gone, water can back flow into your cylinders too. Had this issue happen also with these engines.

 

[olazabel]

i guess it is possible that the stalling is the shift interrupt, the lower shift cable is a little out of adjustment.

I ran it on muffs again tonight for about 30 mins, coolant stayed full, oil still looks and smells ok, but I started seeing some steam coming out of the spark arrestor.. so there must be some water getting in the engine from somewhere. I guess my next move is to pull off the exhaust riser and inspect it and the gasket(s), and if that is not the problem, start considering a leaky head gasket? or worse