What oil do you guys use on your 4.0s?

Vinman

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Shell Rotella T4 15W40 with a Wix 51515 filter has been going in the last four 4.0 TJ’s I’ve owned, never had an issue with any one them. That being said, the jeep is in a heated garage and very, very seldom see a cold start.
 
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Jerry Bransford

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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!
17 isn't cold enough that I'd switch to synthetic. A 5W-30 conventional would be fine for those conditions. :)
 
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Jerry Bransford

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Thanks Jerry,
I drive the same way.
I use semi synthetic 10w40.
What do you think?
I'm not a fan of any viscosity other than what the engineers spec'd for our engines. In 55 years of driving I've never had an engine problem and I've always just used the viscosities the factory recommended. :)
 

jeepins

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Houston, TX, USA
I've only ever used two things in my Jeep. This filter and this oil. Because that's what I started with and knock on wood, have not had a problem with oil or engine trouble in 228,000mi
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Tarek Chamma

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I just did my oil change today.

I wanted to switch to Castrol for this change as it is a premium oil, but couldn't find the Castrol GTX 10W30 synthetic blend (semi synthetic).

So, I disregarded all advise and went for Castrol Magnetic 10W40, I think it is full synthetic... (sorry)

My Jeep is a 2006 inline 6 (4.0 liter), and I have almost 220K miles on it (350K kms).
The average ambient temperature in the country i live in is
15 - 20 degrees Celsius in coldest winter
45 - 58 degrees Celsius in hottest summer and maybe more :(

I bought my jeep with less than 15K miles used different oils since then conventional, synthetic and semi synthetic.
My previous oil that i was running was 5W30 Synthetic blend.

My EOP was:
45 psi on cold start
32-34 psi on Idle (engine hot)
54 psi on 2300 RPM (approx 70 - 75 MperH)
Max Psi is 59 @ full race which i guess the capacity of the oil pump.

Today after changing the Oil to Castrol 10W40 magnetic (Full Synthetic), the readings are almost the same, but i still have to check the readings at cold start.

I am not a mechanic, and most of my knowledge comes from the internet and forums like this, but i have done a lot of work on my Jeep through a professional work shop owned by a close friend, and I enjoy watching upclose and asking him many questions :)
 

LukesfirstJeep

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I'm not a fan of any viscosity other than what the engineers spec'd for our engines. In 55 years of driving I've never had an engine problem and I've always just used the viscosities the factory recommended. :)

Jerry, I agree with you about this topic, and many others, but there's always an exception. I had a 2000ish Volkswagen with a 2.0 gas engine. My local mechanic told me to use a very high viscosity oil, 20W-50 if I recall. The explanation was this is what the engine was designed for, but the lower viscosity was "recommended" for better fuel economy. I put 250,000+ miles on that car and averaged 30 MPG using the higher viscosity oil. Last I heard, the car was still running strong.
 

Legija

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Hey I’m back and with another question guys. Doing an oil change on the 2004 rubicon I just got. Just wondering what oil you guys run. I got 10w-40 synthetic mobile one high millage. I live in California so we don’t get below zero ever haha.. coldest this Jeep might go is Tahoe/Nevada in the winter.. my 90 Cherokee has the 4.0 and we have always done 10w-40 but in my Haynes manual it says 5w-30 for cold and 10w-30 for normal weather. Guy at the parts store agreed with me that 10w-40 would offer more protection.. you guys agree? There may be a thread on this if so I apologize in advanced haha..

also what coolant do these use? The zerex g-05 50/50? Thanks guys!!


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i just change oil in my 1999 Jeep Wrangler 4.0 and i use Motul 10W-40 engine runs so much smoother and seams to be performing better.
 

Potomus Pete

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Dec 8, 2021
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Sarasota Florida
15-40 Rotella like many others. I think it's good, and the price is right. Walmart oil is great for my cars. Oil change for under thirty bucks so I can change it all I want. I often wonder if you can change it too much. When I opened my valve cover it was like new inside
 
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Agamemnon

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Sep 3, 2022
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I run Rotella 10W-30 in mine. Keeps my valves quieter than other oil, and it gets *cold* here (-20 in the winter), so I'm not going heavier than 10W. I've considered running Rotella 5W-30 in the winter, it's just so pricey for T6.
 
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Pantera99

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Sep 2, 2022
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Gilbert, AZ
Oh no, every forum has the dreaded oil thread!! 😳 Valvoline Maxlife 10-30, I believe its semi-synthetic. Seems to have lessened the rear main drip a little. But isn't the saying, Jeeps don't drip they mark their territory?? 😂🤣🐕