Randy Bobani

Pennzoil Ultra Platinum is an excellent motor oil. However, Amsoil uses a slightly better base oil than any other manufacturer on the market. Amsoil protects, cleans and flows better at cold temps than any other gasoline motor oil. That's why if you choose Amsoil, you're spending $80 per oil change. You can save a few $ with Pennzoil Ultra Platinum which is nearly the same quality. In the great north woods where temperatures can drop to -30'f, these two motor oils in 5W30 would be my selection. Closer to the equator, like the blistering temps to 120'f in the southwest, I would run Rotella T6 15W40. Rotella actually contains slightly more detergents and anti-wear additives than any gas motor oil.

RockyMtn96XJ

Precisely. A lot of use use it just for that reason. Seeing as how these 4.0 engines are compared to tractor engines as lot of times and have a lot of mileage on them these days... along with the flat tappets and all that....

Marwell Grimes

I was told by a mechanic of 42 years and a Jeep technician that you should always stick to manufacturers specifications. For example my 02 Jeep Grand Cherokee Laredo 4.7L V8 4x4 requires 5W30 in temperatures between 20°F-100°F and 10W30 in average Temps exceeding 100°F like in Texas or Las Vegas, Nevada. That the spec is made so the thickness is perfect for your engines normal running temperature so the oil lubricates fully inside the engine, that if it is to thick in viscosity like in my case 20W30-20W50, then the oil may not get across all the needed areas of the engine to properly lubricate, and cool the high friction parts. Which reduces wear and eventually non repairable damage.
maybe there is something else I'm not aware of, just figured I'd ask.

Randy Bobani

So an engine oil, with an improper viscosity for the application, literally gets stuck in the pressurized oil passages at even 50 PSI?????

Proper viscosity is primarily determined by bearing clearance and operating temperature.

Proper base oil/additive package is determined by internal engine materials, cylinder pressure, fuel/fuel delivery, average RPM and engine design.

cpttuna

NAPA 30 wt (75-110) and one pint STP every oil change. 264,000+ and going strong

Sandy Deasd

I feel like I've been watching commercials for every kind of oil brand on the market, 😆

00t444e

The 4.7 is a far more modern Eroupean design overhead cam engine that requires lighter weight oil. The 4.0 is a old school AMC pushrod engine with a flat tapped cam that dates back to the 60s, original specs called for as high as 20w50.

Marwell Grimes

"So an engine oil, with an improper viscosity for the application, literally gets stuck in the pressurized oil passages at even 50 PSI?"
No I don't think that's what he told me, he said the oil doesn't flow fast enough to all the fast moving parts causing engine wear. It eventually gets to every part with most oil viscosity but the specified oil flows fast enough to prevent unnecessary wear, in my case 5W30.
said this damage wouldn't be apparent immediately but over time, especially if you took the vehicle to a hotter climate than what the recommended oil is rated for.
He said the number before the W indicated the oil performance at 0°F and the number after the W indicates it's performance at 212°F.

DustyWagoneer

IJM

I think it's actually 0°C and 100°C, respectively, but you've got the right idea. And by "performance" that really means the viscosity at those temps is similar to a straight weight oil at operating temp (100°C). For example, a 5W-30 oil flows like a straight 30 weight oil at operating temp but also flows like a straight 5 weight at winter cold startup temps of 0°C. In other words, multi-weight oils show less viscosity change over a range of temperatures than do straight-weight oils. The "W" stands for winter and not weight, by the way.

Randy Bobani

The 196 called for straight 30 or straight 40 depending on climate. The 199 through 258 engines called for 10W40 until 1979 they switched to 10W30.

00t444e

Read here.
https://www.cherokeeforum.com/f2/rot...essing-188168/

cruiser54

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

exasemech

Come on, quoting what Chrysler says to use. What are you trying to do, ruin all the fun? 😀

IJM

Then again, Chrysler says to use ATF+4 in the AW-4...