Check Mercury's FAQ on their website, it looks like now they are recomending that ALL of their engines use 20-40 Full Synthetic oil. This supersedes all previous recommendations for oil weights in manuals. My manual states 25-40 semi-syn, so I plan on switching to the 20-40 Full-Syn.

am a little concerned about switching to a Full synthetic due to the fact that the engine is well used, and I know in an automotive situation its not advisable to switch conventional- synthetic after a lot of use. But whatever Mercury says I will follow..

Just a heads up for those of you who follow your manuals for lubrication requirements.

Why should Mercury be any different than Harley Davidson, Harley never recommended a synthetic until they had one with their name on it.

A 20w40 synthetic? Not readily available from any auto parts store.

Yamaha, use to run a 20w40 viscosity fluid for decades, a few years back they discontinued it and said you can run a 10w40.

Polaris reccommends a semi syn 20w40, me personally, 20w50.

Ken

No way!!?? What about all the roller lifters that won't be rolling on the cam lobes due to the synthetic oil?? Or... does that, all of the sudden, not happen anymore?

Sometimes I get skid marks in my shorts from eating synthetic foods.

Hope that wasn't too personal. :lol:

Glad you brought this info up. My boat has 30 hours on it. No way do I want a full synthetic put in there at this point, I doubt that it is fully broken in. At best, I'm going to wait till there are more hours on it.

30 hours is plenty of time for break in. And a 40 weight is a 40 weight is a 40 weight. i.e. 0w-40, 5w-40, 10w-40, 15w-40 or 20w40, is all gonna protect the same when at operating temperatures. The reason Merc says to use a 20w-40, is exactly for the reason stated above, because they are the only ones that offer it. So they hope the average person out there doesn't know any better, and "has to have 20w-40", cause Merc says so!

I put synthetic in when they come off the dyno.. Usually Amsoil. Thanks Corey.

Well, yes, Mercruiser is playing their recommendation for their oil against the fear that using any other oil may damage their engine. If there was some concrete proof that their oil specification was not significantly different from aftermarket oils, that fear would not exist. But until that happens, many will use the recommended oil.

The fact is, every oil on the market that is rated at a certain viscosity and meets a certain SAE spec is not the same. Aside from those 2 specs there are myriad other specs and additive blends that can make a vast difference in the performance of an oil in a specific application.

Hemantite, The SAE spec IS the viscosity spec.

The API specs the quality level of the oil.

If 2 different oils meet the same SAE spec and the same API spec, then unless your oil blender is less than ethical, the oils are the same.

The blender may use a different additive companies additive, but if you meet the spec, you meet the spec.

Of course there are 'ranges" in the spec on viscosity, but whether the oil is on the light end of the viscosity range or the heavy side of the range, it still has met the viscosity of the qualified range.

Ken