25hp 2002 4 stroke high speed oil burn

[Foothills]

I have a 25 hp. Mercury 4 stroke--shop has rebuilt upper engine -head gasket-fluxed head rebuilt-carb-have water/fuel seperator-did leak down and compression test( all fine) problem-after couple hours of slow trolling -go to full throttle engine losses power -blows out white smoke from exhaust-( smells of oil)-takes a while and can bring it back to full power--does not do this any other time-shop and Mercury say they don't have a clue--any help??-has low hours boat sat for many years in a garage-

 

[Texasmark]

Re: 25hp 2002 4 stroke high speed oil burn

Try tilting your engine so that the rear of the cylinders are higher than the front. Actually I'd tilt it as far as you could and still get the performance you need. This forces any accumulated fuel to be burned off as it accumulates and may stop your problem. Years ago Merc designed their fisherman series with just such an angle for that reason, to improve the engines ability to slip over stumps and all. Other than that a hotter plug may help as long as it's not so hot as to cause tip overheating at WOT. If running surface gap plugs that is tough to do....overheat the tip.....or you could go to conventional plugs (Silvertip can help with the type I'd bet) which put the spark deeper into the combustion chamber and improves the opportunity for complete combustion.

Mark

 

[Foothills]

Re: 25hp 2002 4 stroke high speed oil burn

Thanks for the reply--the smoke was white in color and smelled like oil--?

 

[Texasmark]

Re: 25hp 2002 4 stroke high speed oil burn

"Thanks for the reply--the smoke was white in color and smelled like oil--?"

"Smells" normal to me...Grin. I have done what I suggested. I had a 115 tower and trolled a lot. Every time I quit and attempted to get on plane, same scenario. After I started tilting the engine, problem disappeared.....oh and if you can get TCW 3 full (silicon previous error corrected) synthetic or even blended it significantly reduces the oil and the problem.

Good luck,

Mark

 

[Foothills]

Re: 25hp 2002 4 stroke high speed oil burn

Mark--thanks again and will give that a try--

 

[Foothills]

Re: 25hp 2002 4 stroke high speed oil burn

Mark--thanks again and will give that a try--

Mark and all 25hp Mercury outboard people-after a lot of leg work and dealing with professional shops that could not figure this one out--and spending more money than the engine is worth-one shop in a split second looked up the service bulletin no. 2003-14 titled "Crankcase oil entering the breather -25four stroke" requiring a new adapter plate gasket which instead of one hole for drain down -now uses 3--it was covered if you had it done in the warranty period-since it is a 2002 -it came out of pocket--I learned to do my home work--dealing with these so called "professional shops" takes the enjoyment out of boating. To the one shop that took some time with me --thank you-