1999 4.3L Mercruiser Consuming Oil (Some Diagnostics Done-What Next?)

[QBhoy]

Yes I do think the oil smells of fuel.

Ok. Look back at what I said originally.

 

[QBhoy]

Which carb do you have on that 4.3? 2bbl or 4bbl? Is the choke opening all the way? (must be an electric choke). Your plugs look very good except that one, so I'd be surprised if you have fuel dilution in the oil. About the only things that would cause fuel dilution would be a choke that does not open (but then we'd expect all the plugs to be black) or a sticky float/leaky needle valve that is allowing flooding. I do recall hearing that the 4bbl Webers that Merc used in some years were prone to that.

Quite common where I am for fuel dilution caused by guys running the engine for ages at idle to charge batteries etc. Especially with the very cold water. The engine never gets to operating temp and pressure.

 

[Gus-SeaRay]

It is a 2bbl carb. I have changed the oil and will do a sea trial today looking at the plug # 6 a few times. Will report back how it goes for oil consumption. I do notice a sound that sounds like a lifter tap on cylinder 6.

 

[Gus-SeaRay]

Took the boat out for a run with the new prop. Oil consumption was about the same. 1/2 a quart over a good 2-2.5 hour of running. Some starts and stops. 3-4 short WOT runs. The new prop makes a world of difference for RPM at WOT. I cleaned plug # 6 before going out and it seemed to stay about the same as what I had cleaned it. It seems there is significant oil around the threads on this plug. I do see some light wetting from valve cover gasket leak on the side of the head. I am thinking that is burning off and maybe is not enough to make a mess in the engine compartment. Possibly get down around the outside of the plug and why the outside around the threads are oily. I saw some trails of smoke a few times (start up and coming off throttle). No evidence of smoke when revving the engine in the water or when taking off from a stop.

 

[dingdongs]

Sounds as if you have done all the obvious tests and all looks well. You could have a blown gasket where oil is going into the water qnd directly out the back.
if you can live with the oil consumption as no other faults until something gets a lot worse it willsave considerable expense or just get another complete engine new especially if used in salt water as internal galleries is hard to find if not inthe heads or the manifold by which time you have spent half the price of a new engine and you could sell the old one complete andget some money back too.

 

[Gus-SeaRay]

Something else I observed but really didn't connect it to the oil consumption issue. After thinking about it thought I would mention to see if it added any new thoughts. I notice that after on plane and at around 3000 rpm or at max rpm. There are random times it feels like a slip or like a hesitation. Reminds me of water in fuel but not as long of a pause or interruption to power. Wondering now if that is a random misfire and may not necessarily be related to water in the fuel. Will pull the fuel water separator to look for water evidence.