Mercruiser 3.0 Oil coming from crankcase ventilation hose

[Daritzz]

I have a 1993 Mercruiser 3.0L and noticed oil leaking from the rubber elbow hose which runs between the crankcase ventilation valve and the flame arrestor, the hose attaches to a bracket which holds the flame arrestor in place. Also noticed that the oil leaks out of the hose when the boat is running in water, no leak when it's idling on driveway with water running.

Is this normal in these engines given it's an open valve to the engine? I bought the boat recently and can't say if this is something recent or happened in the past.

Thank you,
Greg

 

[HT32BSX115]

Re: Mercruiser 3.0 Oil coming from crankcase ventilation hose

Howdy,

This means that you have *some* blow-by. ALL engines have a measure of blow-by depending on how worn out they are. If it's brown it's probably ok to certain degree.

You won't get a lot running in the driveway since the engine is not loaded much. In the water you're loading the engine and you'll have far higher cylinder pressures hence more blow-by.


If it's white, you've probably got some water in it. That's a whole lotta different.

The easy way to know is with a compression test.

And specifically a cylinder "leakdown" test.

Cheers,


Rick

 

[Daritzz]

Re: Mercruiser 3.0 Oil coming from crankcase ventilation hose

when i purchased the boat i had a mechanic take the compression test (again on the drive way) and it read 120 across all 4 cylinders. The oil leaking is brown in color and i ran it for about 2 hours on the water with about a table spoon of oil accumulation on the engine. Does that seem as too much for normal misting?

Thanks,
Greg

 

[juels98]

Re: Mercruiser 3.0 Oil coming from crankcase ventilation hose

Is there a clamp holding the hose in place, or does it just pop off on it's own? Mine didn't have a clamp and the valve cover had oil on it. Since the clamp was put in, it's all good.

 

[jerryjerry05]

Re: Mercruiser 3.0 Oil coming from crankcase ventilation hose

A comp reading of 120 on all 4 is probably just the tester all testers will read different.The main thing is the cylinders all read the same.To really test it for blow-by you need to do a leakdown.But too much oil can be rings,valves seals.J