20W50 vs. 15W40

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AFAIK,
15w40 is primarily marketed/formualted for HD diesel engines, while 20w50 is aimed at the gas-powered crowd.
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A 15W40 is going to have a much better aditive package and will more then likely be less volitile! 15W40's usualy are shear stable were most 20W50 shear badly some down to a 30Wt.! If you want a good 15W40 Delo 400 and Delvac 1300 are the easiest to find and have excellent formulas. If you can find them in their CI+4 form they are even better! 15W40 has better performance in it's dino form at both hot and cold extremes then most dino 20W50's!
 
Bear in mind that, although I am a big fan of the all-fleet oils (Delo, Rotella, Delvac, etc), they are generally not recommended for use in strictly gasoline-powered fleets because they have a greater tendency to foul spark plugs. I believe this is due to their much higher DD additive levels. Most 20W50 oils would not be susceptible to this issue. In my experience, most 15W40s will not cause troubles either, but if you start fouling plugs more quickly/frequently, go back to a 20W50.

For my part, I have not experienced 20W50 shear-down.
 
quote:

Originally posted by bulwnkl:
For my part, I have not experienced 20W50 shear-down.

I don't know why 20w50 gets such a bad sheering rap. The amount of viscosity index improver in it should be similar to that of a 10w30 and therefore (if that is true) the 20w50 should be more sheer stable than a 5w30 or 10w40.
 
quote:

Originally posted by bulwnkl:
Bear in mind that, although I am a big fan of the all-fleet oils (Delo, Rotella, Delvac, etc), they are generally not recommended for use in strictly gasoline-powered fleets because they have a greater tendency to foul spark plugs.

This is news to me... My Jeep doesn't burn oil though. I'm using Delvac 1/M1 T&S
 
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