Oil,Oil,Oil
I received this response on this question... Thought it would be good to share it....
Quote
"Here goes.
First we'll talk about conventional multi-vis oils. A straight 40wt conventional oil is pretty much 40wt stock. Simple enough. A 10w-40 conventional oil is NOT a mix of 10wt stock and 40wt stock. Listen closely: it is essentially 10wt stock with a boatload of viscosity enhancers in it. These are long strands of hydrocarbon molecules that "get in the way" of the 10wt stock flowing out of wherever it is. While this sounds scary, it works very very well.
BUT
The long molecules eventually get torn apart over time, leaving the oil thinner than desired. Some applications are easier than others on the long molecules. One application worth noting is a motorcycle, which shares its gearcase and wet clutch lube with its engine lube ('cept Harleys, so don't get in a wad over it). A bike transmission will shred the viscosity enhancers MUCH QUICKER than just about any other application. For this reason, a bike's change interval is more important than a station wagon.
Now, in a big block Chevy, whether it is in a blower boat or a grocery getter, there is no thrashing gearbox to shred the molecules, and no wet clutch to contaminate the lube, so it's not nearly as big of a concern. Theory says, though that it is a noteworthy concern regardless of whether your application is severe or not.
So with conventional multi vis oils, the "narrower" the winter and summer ratings (10w-40 is "10 winter, 40 summer"), the "purer" and more stable the oil will prove to hold its viscosity over time. A 15w-40 is "better" than a 10w-40. Merc's 20w-40 is even better yet.
Synthetic lubes DO use the same practices of using viscosity enhancers where needed, BUT in the case of a syn lube, the high number is a hot equivalent, and the low (Winter) number is a cold equivalent. In many instances (10w-40 syn) there is essentially ONLY 40wt equivalent syn stock with almost no viscosity enhancers at all. This is good stuff. It is possible because synthetics are DRAMATICALLY more "pourable" at low temps. Since the rating system is based on dino oils, the syn oils are all "equivalents" and not actuals. Modern 0w-30 syns DO use enhancers.
Another thing worth noting, is that commercial fleet oils are indeed a stouter and "better" choice. Specifically the conventional Rotella and it's Delo cousins are favorites of over the road fleet operators. As far as it being a "diesel" oil, feel free to check the extensive ratings stamps on the bottle (or jug as it is with that stuff). The API and other certifications will show you that of course it is suitable to run in a gas motor. Many of the consumer oils are processed by using clay in the refining process. This leads to a substantial amount of paraffin left in suspension in the lube. This is a Group 1 oil stock. Rotella and other fleet oils use a different method of refining and will practically eliminate the waxy buildup you find in a high mile motor (especially in the seals and under the valve covers). It;s mostly Group 2 stocks.
Synthetic Blends and many "synthetic" oils use a high grade of conventional stocks called Group 3. The refining method of obtaining these stocks is called "hydrocracking" and delivers a very nice oil stock that more or less performs halfway between Group 1 and Full Syn oils. These are nice oils too, but are not true synthetics. Be aware that Mobil 1 is now formulated in some Group 3 stocks ever since Mobil lost its lawsuit over other mfrs claiming that their Group 3's were full synthetics (can't beat em join em). Red cap Mobil 1 is still full synth.
BUT the Rotella is in many cases a better choice for boat oil (and motorcycle oil). It comes in 15w-40 and is chocked FULL of all the good stuff and the additive and detergent packages are far far superior than what we get in our bottle of consumer oil.
If you want to go all out: RP, Amsoil, Mobil 1 motorcycle oil, Delo synthetic, and Rotella synthetic are all mega oils. Can't go wrong.
As far as viscosity? This was the original question if I recall...
I see no need to run 50wt anything in a motor built to run clearances based on 40wt oil. If you PLAN to build a 50wt motor, and set it up from the ground up for 50wt then fine - otherwise I feel it's a waste. Waste of fuel and horsepower. Size your bearings, lifters, etc. - set your clearances, and such for the hp and temps and then run the correct viscosity. That's my thoughts."
End Quote
I am going to call rotella... I know its a good oil... its all i use in my diesel.... but im thinking Kendall gt40, Valvoline vr 40, or merc's 25w40 will be it...
Merc told me that thier 25w40 is a straght weight but has pour properties of 25 when cold... I wonder if its not a syn blend...
I was hoping to get a better answer... But.... It sounds like the best option out there...
