above 4K I get a heavy waft of crankase fumes in the cockpit. Definitely a stench of oil fumes, not fuel. Linearly worse as you go from 4K to WOT.

No leaks, proper level, M1 15/50, Wix filter, bla bla bla...

This is not new as I remember, but I don't remember it being this bad.

I guess I need to make a quick stop from WOT (which I hate to do) and really see if it's heavy in the bilge.

Until then, any ideas?

Thanks.

Just a thought. When you change the oil filter it is difficult to keep oil from running down on the exhaust manifold. This will cause a strong smell for a while, If you have done this recently.

no, I wrap rags...no mess.

like I said it's always been an issue, it just seems worse this year.

Do you believe the smell is coming from the breathers/crankcase and if so, how much oil are u burning? If excessive you may want to start with a compression or cylinder leak test?

Good luck

The 496 engine has a built in orfice in the bottom of the intake manifold that is .080" size and when the engine is running it keeps a a slight negative pressure in the crankcase. There is a fresh air into the crankcase that pulls fresh air into the throttlebody in the throat and down an intake manifld passage into the bottom of the oil fill tube. If you take your oil fill tube cap off at idle is there a slight vacumn? There should be. Also see what the oil fill does with the cap off at 4K rpms. If your crankcase pressure (due to blowby, etc.)is high this pressure can force oil vapor back into the intake manifold and some vapor back out the flame arrestor on the throttlebody which you could smell if its doing that. Also with your motor off and flame arrestor off, open the throttle full open and look down inside the manifold intake opening and see if the inside looks moist or wet with oil, this can be a good indicator of what is possibly happening. If you see that I would suggest a compression test with a leakdown test. Stock 496's should have about 150-160 psi cranking compression in each cylinder ona cold engine. Hope this helps, hope its something simple.

Ray @ Raylar

Thanks Raylar! I will take a look at these things. I have never had to add oil between changes (30-40 hours). Also the boat runs well. Pulls RPM, both run identical R's at all speeds to WOT. Boat runs appropriate top speed. Wouldn't I have a performance loss if I had one or more weak cylinders?

Rippem
Did you ever figure out what was causing your crank case fumes? I just noticed mine was starting to smell the other day.

Check your drive lube also, right before mine twisted off the vertical shaft there was a strong oil smell in the cockpit, it had puked a small amount of drive fluid out of the reservoir.