Jeep 4.0 "perfers" 40 weights

[JeepZJ4.0]

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Originally posted by XS650:

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Originally posted by JeepZJ4.0:
I dunno Jon... not to start a fight or anything but i know 20psi at speed is the low side. 40 is right in the middle. Mine runs about 45psi with 10W30 oil.

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Is that actual oil pressure off an accurate gauge, or from the Jeep gauge?

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LoL...... the Jeep gauge.... aka..... it's never right.....the sensor costs 25 bucks so i hope it works right.

 

[XS650]

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Originally posted by JeepZJ4.0:

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Originally posted by XS650:
Is that actual oil pressure off an accurate gauge, or from the Jeep gauge?

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LoL...... the Jeep gauge.... aka..... it's never right.....the sensor costs 25 bucks so i hope it works right.

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YOu could plug in a good gauge for a while to chyeck your Jeep gauge and see how far off it is. Typical factory automotive gauges may be crap, but they are fairly consistant crap, so the error should stay the same over a long period of time. Like years if you're lucky.

 

[TallPaul]

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Originally posted by JonS:
I e-mailed Havoline a while ago about this and their response was that 10w-40 might not raise the pressure ...

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10w40 raised my pressure to 45 psi hot at 2000 rpm vs 35 psi with 5w30. Also boosted idle pressure from 16 to 22. This is not a jeep, but a Ford 300 inline six. I did this to get into the spec range of 40 to 60 psi at 2000 rpm.

 

[MNgopher]

I agree with the other statements that this beast will run so long as there is ANY oil in the crankcase.

FWIW, my '88 owners manual for my XJ suggests anything from a 5w20 to a 20w50 is appropriate for this motor depending on outside temps.

I switched to a 5w40 last year from 5w/10w30 (depending on winter vs summer) regimen. I haven't documented any difference in fuel mileage from the previous years mileage during the same period, and I take excellent records on that!

There is some UOA evidence to suggest that the xw40's do perform better in engine wear than the xw30's, but then there are good results on xw30's too.

Short story: Use any modern multi vis oil between 5w30 and 20w50 and you will be fine!

 

[MNgopher]

And FWIW, my oil pressure did not change noticeably between 5w30 and 5w40. On the Jeep guage, I get 60 psi cold, 25 psi hot idle, 50 psi cruising hot.

 

[KW]

On the factory guage I see about a 5 PSI increase at hot idle between Mobil 1 5W30 to 0W40. At cruising speeds it's the same at about 50 psi.