New 496HO....15hours. After WOT run, slight leak near the back of the motor. Is there a vent or relief at the back of the crankcase or maybe the oil pump? Is this normal?

-Craig

This is not normal, mine does not leak a drop. Any time I have experienced a leak from the back has been a rear main seal.

I've owned 3 496HO's and haven't ever seen a drop of oil leak out of any of them. Sometimes they burn a bit, but haven't seen one leak before. Something is wrong and you don't want to wait to deal with it until after the warranty's up, assuming you have a warranty for it.

John

Thanks for the response guys.

Rear main seal is what I was thinking too. Just seems strange on a brand new motor. It didn't leak at all until 10 hours. Thought maybe therre was a relieve valve on the oil pump which is back in that area too.

Anyone else seen this on a 496?

-Craig

My 496 developed a leak within the first 5 hours. It turned out to be a cracked elbow fitting where the oil pressure sensor screws into the block. See part number 44 in this diagram.

http://www.mercruiserparts.com/Show_...ft+and+Pistons

Looks likes there are a lot of potential connections and plugs at the rear of the block and case that could leak if not tightened properly. I’m gonna have to try and get down in the bilge and see how many of them I can see/reach and if any are loose/broken.
-Craig

If its anything other than the analog oil sensor fittings on the back top of the block, get it to a Mercury dealer and let them figure it out on warranty. Don't start trying to repair things yourself while you're on warranty, that could void the warranty. Let Merc handle it, thats what warranties are for.

Regards,
Ray @ Raylar