I'm looking at jug of Rotella 5W40....don't see anywhere on it the word diesel.

 

It might not say diesel. The difference is the class of the oil. There is a "star burst" on every oil container and there is two letters on it. It will either be C* or S*. C stands for compression ignition or "commerical" and S stands spark ignition. Diesel oils tend to have a higher temp rating for piston oil cooling jets and turbochargers. It also has more zinc and whatnot. As far as standard spark ignition engines go, the zinc content was reduced for fear that it would slowly kill the TWC. Rotella is a great oil, great for some HP applications. My dad has a ranger with 326,000 mi on it and he ran advance and oreilley's brand oil for 300,000 of it. No smoke, just a little lash adjuster tick(lifter). Changed to Rotella just for Ss&Gs and it quieted down the lifters. The noise isn't gone, just quieter. Most parts store brand oil is havoline which seems to be good stuff for 300k miles with no sludge. Castrol is real good stuff too. I ran it for years before times got hard and I had to go cheaper. Just my .02

 

I was being facetious.....great post though.

 

Jeep Engine Oil Viscosity
This was taken from pages 82 and 83 of the 1989 Chrysler/Jeep owners manual.
Selecting Engine Oil Viscosity
When changing or adding engine oil select the proper grade by using the chart on the following page. Select the grade that corresponds to the ambient temperature range you expect to encounter before your next oil change.
30*F to 100*F+ 20W-40 or 20W-50
0*F to 100*F+ 10W-30 or 10W-40
-20*F to 60*F 5W-30

 

same as my manual. but according to bobistheoilguy, 10w-30 can be pretty thick at start-up. Would 0w-30 be too thin?

 

Does Bob have a Jeep and the corresponding owner's manual?

 

another thought is the 5 or 10 - 30w mobil1 high mileage. it's SL rated which gets around the 800ppm zinc limiit of SM and SN oils. the mobil1 high mile has 1100ppm which is more in line with 90s oil. i tried it the other day in a briggs vanguard engine {air cooled commercial grade} and it REALLY cut down on the cold slap. engine runs much quieter now. it's also going in the cherokee next oil change. had been using it for awhile in my integra type r just to cut down on oil consumption.

 

I've run 10-30 in every 4.0 I've owned.

Regular maintenance has much more to do with engine longevity than viscosity

 

And a quality oil filter...........

 

Pop quiz....

Which oil is thinner at operating temp?

A. 0W30
B. 5W30
C. 10W30
D. Straight 30
E. They are the same

Which oil flows better at below operating temp? A, B, C, D above.

 

Err, well, yea

 

Probably more important than weights of oils. I don't care what oil you run if your oil filter has drained down since the last shut-off and is full of only air.

 

0w-30 is the thinnest at startup, so it would flow better under operating temps. Am i right?

 

True, but he didnt really specify it to a specific car, he actually made a point of saying it applied to all makes and models of all ages.

 

You guys are really overthinking this...........

I live in the mountains of Arizona. I run 15w-40 Rotella in both my Jeeps year-round. We see temps from 0*F to 100*F.