I've read several posts saying the 4.0 likes a 40 weight oil. What is this based on? I know it's an older design, but I've followed the owner's manual and used 10W30. What's the deal?
Citgo Ultralife (high mileage) 10w30 lists a 100C viscosity of 12 cSt. Compare Maxlife at 10.5 cSt.quote:
Originally posted by MarkC:
Maybe I'll just try one of the heavier 10W30's.
Thats a 10k mile oil in the right engines/driving conditionsquote:
Originally posted by TallPaul:
Citgo Ultralife (high mileage) 10w30 lists a 100C viscosity of 12 cSt.quote:
Originally posted by MarkC:
Maybe I'll just try one of the heavier 10W30's.
The mid 90s Jeep oil pressure spec for the 4.0 is 37 psi @ 1600 rpm. Don't know what the '88 spec is, but perhaps you were fine with a 10w30.quote:
Originally posted by MNgopher:
The 5w40 stays right at 60 psi, even during an 8 hour run in 95 degree weather.