Mercruiser 454 oil leak mystery

[siposta]

My 1990 Mercruiser 454 has about 60 hours after being rebuilt. I have an small oil leak that appears to be at the joint after the oil pan and before the transmission. I removed the bell housing and found the area, including the flywheel, relatively dry. I notice a small amount of oil under the distributor (shaft gasket worn out). I checked the obvious points (oil pan seal, oil pan drain, dip stick base hole, and oil pressure sender) - all appeared "dry". I pulled the starter - it appeared to be relatively wet.

This is an annoying leak!

Suggestions and solutions would be greatly appreciated.



Tom S.

 

[EddiePetty]

Re: Mercruiser 454 oil leak mystery

If the Big block is like the Small block and the oil pressure sender is beside/under the distributor, the crimped joint between the Bakelite head and steel housing of the sending unit was prone to leakage after being man-handled. Wrap a paper towel around the unit to confirm.

 

[hottoddie]

Re: Mercruiser 454 oil leak mystery

Could be the rear oil pan gasket weeping. Try to get underneath and snug up a little on the oil pan bolts. Or maybe the rear main seal is weeping. If only 60 hours no easy fix for that however. Use mirrors and maybe a litttle dye in the engine oil to help locate. Mercs are a pain because they are black.

 

[tpenfield]

Re: Mercruiser 454 oil leak mystery

the gaskets on the 454 Mark IV engines needed some silicone sealant in the front and rear area of the oil pan as that is where that gasket pieces overlapped.