Crankcase oil smell at speed

[SFCobalt220]

]Hello,
I’m a new 1999 220 owner. The boat runs great, good power and seems to run clean...... But at speed anywhere over 3000 rpm we get a crank case oil smell in the boat. Increase with rpm... No smoke just a oil smell that smells unburned. At times it’s pretty bad.
7.4 Mpi with 800 hrs. Impeccable service history...No oil consumption or leaks found....
20 hours since it’s last major 100 hr service. Everything looked good......oil is clean and not over full.
It smells to me like PVC/ crankcase fumes. Is it a closed system? It looks like a valve over vent tube goes to the intake manifold...?
Any help appreciated.......Thanks

[Big Block Power]

Welcome from Wisconsin. Maybe one of the members that has your same engine as yours will chime in. Lots of time the pcv goes to the spark arrestor. Is yours factory?

[Big Block Power]

Is this what yours looks like. It goes from the port vc to the intake.

[cmattj]

As BB mentioned follow your valve cover pcv and to it’s location. If it’s acessable ...pull it while at idle and see or feel if pulses are coming out . Hopefully it’s going underneath the flame arester. Or hooked to it.

It sounds like blow by venting so we’ll need you to trace it for running it.

[SFCobalt220]

It looks all hooked up and original.... I have not taken the plastic covers off and followed the tube..... I’ll check that tomorrow....

[SAB220]

BTW - a crankcase oil smell to you may be unburn't fuel smell to me....

[Big Block Power]

Check for oil leaks and when you get her going she runs warmer and starts cooking the oil.

[AsLan7]

Hey, welcome to the CobaltChat forum SFC220. So glad you found us.

Sorry to hear about your burning oil smell woes. That sure sounds like a worn positive crankcase ventilation valve as mentioned above. When you get up in RPM’s, the pressure created by a worn PCV valve can allow excessive oil to seep into the combustion chamber (which you’d normally smell on the exhaust side) and/or past gaskets that are designed to keep oil out. If the oil seeps onto the external engine somewhere and heats up enough to cause that burning smell, your valve is not doing it’s job of returning the correct amount of crankcase vapors to their proper place.

Or you could just buy nose plugs and hand them out to everyone.

Keep us posted. ....and welcome aboard mate.


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[SFCobalt220]

Thanks for all the input, I checked the PCV valve, it is on the valve cover and the hose goes directly into the intake manifold. Actually to the upper runner area and when the boat is running with the hose off it pulls a serious vacuum, the check valve seems to be working when I manually pull vacuum through it. But it looks original, still has the factory black paint on it. Maybe it’s weak and leaks at high rpm. I’m not finding any oil residue in the captains call or any water discoloration. But again it only happens at 3000 and up. I do have a small oil leak dripping on the left side front of motor near the power steering pump. Pretty minimal. I cleaned everything and will change the valve and see what happens......

[cmattj]

I do have a small oil leak dripping on the left side front of motor near the power steering pump. Pretty minimal. I cleaned everything and will change the valve and see what happens......

I’m glad your pulling vacuum, and I’m sure you visually looked to see if there are any signs of blow by “ , coming from the valve cover pcv grommet when you had it out.

A indication of too much crank case pressure on marine motors with limited breathers( just pcv) is the oil dip stick will actually pop up slightly. It’s the path of least resistance when crankcase pressure gets high . So keep an eye on that.

As far as a minimal leak..?? Well merc follows A lot of auto makers who paint engines black because it’s hides everything seaping or leaking.

Get the leak fixed as it’s probably a oil filter oozing and there directly over the exhaust manifold. If your not sure change it anyway and top it off.

Good weather is here so time to go play!!

[SFCobalt220]

The filter base is clean, it may be the valve cover. I cleaned everything and now I can hopefully pinpoint it. If it is an oil leak burning off, do u think it would make enough that it could pull/push out of the engine bay vents at the rear and still be able to smell it? We don’t smell exhaust just the oil odor. Never see any smoke or odor when we open the motor hatch either....

[cmattj]

The filter base is clean, it may be the valve cover. I cleaned everything and now I can hopefully pinpoint it. If it is an oil leak burning off, do u think it would make enough that it could pull/push out of the engine bay vents at the rear and still be able to smell it? We don’t smell exhaust just the oil odor. Never see any smoke or odor when we open the motor hatch either....

Well considering boats have the “ covertable effect “ and blow stuff forward it’s possible.

It may not be broken or leaking enough to pin point. See keep her topped. Do a pre.. during and after inspection and enjoy it.

[Big Block Power]

You could boat like others and just cruise the coastline and never go above 3000 rpm. Lol

[cmattj]

You could boat like others and just cruise the coastline and never go above 3000 rpm. Lol

Why so fast? My mpg will suffer...