98 Jeep Cherokee, what oil is spec'd?

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The spec oil for the vehicle is 10w30. The manual, if you had one, would only suggest 5w30 for colder temps. Shear in 5w30 was more of a problem when the vehicle was built than it is today.

I have owned 3 of those in line Jeep sixes, and studied countless UOA's and had some of my own done as well. While the Jeep 4.0 will seem to run happily on almost anything, if you really want what is best for the engine you should choose a thick for grade 30, (such as Rotella 10w30 or Pennzoil HM 10w30) or a light for grade 40 (such as Castrol 0w40).

Most will tolerate thicker oils like 10w40 or even 15w40's, but that is overkill in anything but a badly worn engine IMO. The sweet spot is a thick for grade 30 or a light for grade 40.

If you must use 5w30, try to find a "Euro" oil that will have a higher HTHS.

Enjoy your Jeep!
 
I had a '98 XJ and I agree with your points, KCJeep. I tried pulling the specs for Penzoil HM 10w-30 Plat and vanilla. Unfortunately they don't list HTHS which is an important spec for me. Which is why I use M1 (they list more specs) in my, similar, Ford 4.9L. Looks like the vanilla Penzoil is similar to M1

Penzoil HM 10w-30
KV@ 40C cSt 78.8
KV@ 100C cSt 11.8

Penzoil Plat HM 10w-30
KV@ 40C cSt 65.1
KV@ 100C cSt 10.6

Mobil1 HM 10w-30
KV@ 40C cSt 78
KV@ 100C cSt 12.1
HTHS 3.5
 
Originally Posted by ammolab
Originally Posted by Chris142
The owners manual says 10w30 down to 0F and 5w30 below that.


Yes, but odd that the manual shows that 5W-30 is only good to 60F. I would argue with that.


My 89 manual says the same thing, I guess they didn't trust 5w30 over 60F back then.
 
ACEA is also another important spec for me.

Penzoil HM 10w30 - no ACEA spec

Penzoil Plat HM 10w-30 - no ACEA spec

M1 HM 10w-30 - ACEA A3/B3 (vanilla is A5/B5)

For reference:

M1 HM 5w-30 - ACEA A5/B5 (same for vanilla)
 
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