What oil do you guys use on your 4.0s?

Germanshepherd

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pennzoil 10w40 dino. tried running mobil 1 synthetic once and got RMS leak within days after the change when I never had a leak before. put in the dino 10W40 and not a drop of oil leaked since. not sure if its because of the thicker weight or dino but no more leaks. I also used bars leak RMS as well but that did not help when I had the mobil 1.
 

Jerry Bransford

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pennzoil 10w40 dino. tried running mobil 1 synthetic once and got RMS leak within days after the change when I never had a leak before. put in the dino 10W40 and not a drop of oil leaked since
I also prefer conventional motor oils in my TJ so long as I don't move to the frozen north where synthetics flow better in extreme conditions. I would not run a 10W-40 though. The factory recommends nothing heavier than 10W-30 and 10W-40 is just harder to pump and get into the nooks and crannies. The old days of running a heavier viscosity oil as engines age is also outdated, that was done before today's engine tolerances got so tight as they are now. I sure wouldn't run anything heavier than 10W-30 in any of my high-mileage cars or the Jeep. :)
 
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PCO6

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I stock up when it goes on sale at Canadian Tire.

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jeepXcore

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I used Castrol GTX High- Mileage 10w30 Full Synthetic on my first and only oil change so far.

When I bought the truck, I'm pretty sure it had conventional oil(oil pan has a leaky seal that kept forcing me to top the oil off since I'm not willing to pay $300 for the mechanic to repair it). Since using the high mileage synthetic, the leak has all but disappeared and I haven't had to top it off for 5 months so far.
 

StG58

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Mobile 1 10W-30 and a NAPA Gold filter. The oil is overkill around here, sure, but the old girl deserves a treat once in awhile. Doesn't she? (I used to run M1 5W-30 with no issues, but randomly decided to start using 10W-30 instead) 1999 SE, so technically not a 4.0.
 

Tarek Chamma

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interesting information regarding this subject in the below link:


The country I live in is hot as hell, I used both 10W30 & 10W40, my oil preference is Castrol, as it has a very good reputation of not breaking up, but i have used Mobile and other brands as well.
I use 10K oil and change it every 10,ooo or 12,ooo KMs. as for oil filters, I usually use Mopar OEM.

My oil change is due now, planning on Castrol and i bought the below 3 oil filters from amazon which i will be using in the upcoming oil service for a change:
Purolator PL14670 Blue Single PurolatorONE Advanced Engine Protection Spin On Oil Filter
FRAM HP3 High Performance Spin-On Oil Filter
Pennzoil PZ-19 Regular Spin-on Oil Filter

The manual recommends 10W30, but after doing some research and reading the link above, i think i might go for 10W40.
 

Lilbomb

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I also prefer conventional motor oils in my TJ so long as I don't move to the frozen north where synthetics flow better in extreme conditions. I would not run a 10W-40 though. The factory recommends nothing heavier than 10W-30 and 10W-40 is just harder to pump and get into the nooks and crannies. The old days of running a heavier viscosity oil as engines age is also outdated, that was done before today's engine tolerances got so tight as they are now. I sure wouldn't run anything heavier than 10W-30 in any of my high-mileage cars or the Jeep. :)

Hey @Jerry Bransford , this being said I lived in the Bay Area and ran conventional in my '99 4.0 I just moved to Reno and it's regularly 17-25 degrees in the mornings when I go to work. It has 140,000 miles on it roughly. Would you recommend I switch to a synthetic during the winter months? Thank you!
 
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