Exhaust sheen in discharge FWC 350 ?

One engine 350TBXL has a bit of smoke on start up and while at idle, my other engine is clean. This same engine also has had periodic discharge sheen which seems to be increasing....( could be paranoia) We went to synthetic oil last year which made some improvement. Both engines are smooth runners and I don't see much smoke underway at all from either. Distributors, plugs, wires rotors all new this past fall and new ignition modules.

I recently checked my oil levels and that same engine with the exhaust sheen and a bit of smoke (black) took a quart.
The clean burner was fine. So I'm thinking I have leakage....or a bad seal.

This is a great site and I have gotten some good helpful tips here....given a 1996 engine, my mechanic wants to start with the oil cooler and look for a possible leak there as his first and best guess. I guess I could continue to monitor, but with what could be an original oc should I be looking at replacement anyway? Any other best places to start with these symptoms ?

Maybe...a pressure test will tell you for sure...

How many hours ??? where is the boat used? Going to synthetic on a worn engine is a definite potential for increased oil consumption

20 years is a long time for the oil cooler used in salt water. Like MM says, thin oil will sneak past valve seals and cause smoke, classicly seen at startup.

Check compression

makomark said:

Maybe...a pressure test will tell you for sure...

How many hours ??? where is the boat used? Going to synthetic on a worn engine is a definite potential for increased oil consumption

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Hours supposedly about 500 with an overhaul in 2013....fishing in NJ inshore and mid range. I did not do the MOH. Given what could be original or older oil coolers, I was considering replacing them.
This issue was present prior to going with synthetic and seemed to improve this season....because the same engine that throws the sheen was down a quart, I was paying more attention to the discharge. This engine isnt smokey underway, but does have more smoke than the other one at idle in the slip etc.

are you sure the sheen is due to oil (vs fuel)??

Have added oil twice after last few trips....Port engine not required.

Also have 'soot' black stain on stern Starboard low near exhaust port, I have a swim platform so not obvious but its there now. Now have Ignition issue so starting another thread on that....ugh.

marginal ignition -> partial fuel burn -> sheen in water & soot on the transom....

makomark said:

marginal ignition -> partial fuel burn -> sheen in water & soot on the transom....

Click to expand...

So my follow now that the weather broke....mechanic went looking to replace the Engine Oil Cooler....and there isnt one?!
Have tran oil cooler, but, cant find an engine oil cooler....its also not shown anywhere in the cut sheet diagrams in my manual.
We are both mystified...how is this engineered ? Are we dopes? Our research indicates Crusader did offer the engine without an engine oil cooler.....anyone have any insight on this ?

( we are now looking at the valve seals for the oil burning )

The older SBCs (model 270) never had engine oil coolers....can't say I've ever seen one on a Mercruiser SBC either....only on the BBCs