Jeep 4.0 - Valvoline Premium Blue 15w40

84_Sheepdog · Mar 30, 2016

Would Valvoline Premium Blue 15w40 be a good oil to run in the Jeep 4.0 inline six (2004)? The engine only has 24,000 miles on it if that matters. I've heard due to the design of this motor that diesel oil would be beneficial. Is this true or just a myth? The manual specifies traditional 10w30. The Jeep is used offroad quite a bit so I thought this oil might be beneficial since it is run at steep inclines/descents and occasionally sees low oil pressure as a result. I also run this oil in my truck so it would be nice to just purchase and carry one type of oil for both. Sorry for the newb question, any input would be greatly appreciated.

901Memphis · Mar 30, 2016

I don't think it's a myth, they seem to like the thicker oils. Some of the guys run 0w40 or 10w40 but 15w40 is okay too if it doesn't get too cold.

HemiHawk · Mar 30, 2016

Like Memphis said, you should be OK running it, assuming its not too cold. I know my 4.0 has a tough time starting in the cold, adding a thicker oil would probably only make that worse. But if you're in TX, and running it decently hard, you should be ok with that weight.

From my "research" some of the best oil analysis comes from using Rotella T6 in the 4.0. But that most quality 10w-30s work well.

24,000 miles, thats a gem you have there.

ShotGun429 · Mar 30, 2016

Great choice. Indeed use it.

SwampSurvivor · Mar 30, 2016

I don't think it would cause any issues. A lot of people run 15w-40 in these engines and love it .

My 4.0L and a friend's 1990 4.0L do not like anything heavier than a 10w-30 - they developed a legitimite "lifter tick" until they were warmed completely up.

My friend's 1990 with >200K miles is whisper quiet idling with 10w-30. We had the great idea to dump 20w-50 in it when it had a pretty severe rear main seal leak (about a quart every 35 miles) and all that did was make it sound like the top end was not getting any oil.

My 2000 has a case of piston slap - that doesn't go away with thick or thin oil. But the valve train is much quieter with 10w-30 or even a 5w-20

Your 4.0L engine is 12 years old. The benefits of higher ZDDP went away once the cam lobes were work hardened.

Chris142 · Mar 30, 2016

I have ran 15w40 in mine. Seems to run better on thinner oil,more power.I have been using 10w30 since. @158k now

xshoex · Mar 30, 2016

My 4.0 has seen 15w40 multiple times

Dyusik · Mar 30, 2016

15w40 is fine.

BrocLuno · Mar 30, 2016

I'd do it

gomes512 · Mar 30, 2016

There was a post on Jeep Strokers by a user named 1bolt that tried to determine if 30 or 40 weight oil was better. He collected 20-25 UOA's on the 4.0 for each weight and averaged them. Turns out there wasn't really much of a difference in wear metal numbers. The 30 actually had slightly lower values but I don't believe they were statistically significant.

I used to run 15w-40 in the '94's 4.0 but as Chris142 mentioned it seemed to rob power. That 4.0 slow was already having a hard time towing my trailer. I loved the motor for some reason, wish I still had that truck.

But yeah if you got the 40 weight already then no harm in running it.

totegoat · Mar 30, 2016

Last change, I used M1 5w-30. Starts easy and runs fine, although I can't really tell any difference from 10w-30 dino.

My 04 4.0 TJ has 35,000 on it.

Greg L · Mar 30, 2016

These engines aren't too picky.

Take into consideration the temps in your area, also.

When I had my 1991 Cherokee for 20 years, I kept it on a diet of 10w30 year round in Norhtern Calif (temps were lows 30's, highs 90's)

Tried 15w40 once, but it was too sluggish.

One of the best American engines ever, in my opinion.

SwampSurvivor · Mar 30, 2016

Originally Posted By: Greg L
These engines aren't too picky.

Take into consideration the temps in your area, also.

When I had my 1991 Cherokee for 20 years, I kept it on a diet of 10w30 year round in Norhtern Calif (temps were lows 30's, highs 90's)

Tried 15w40 once, but it was too sluggish.

One of the best American engines ever, in my opinion.

As a "thin oil" believer, mine was even content running 10w-30 this winter here in Central NY state. That's what I will probably run until the engine is no more.

It had no issues with 5w-20 but I'll stick to what was called for originally

Eddie · Mar 30, 2016

I ran my 1995 JGC 4.0 with the recommended 5w30 for over 170,000 miles in Northern IL. Sold it running great without any oil related issues except the real main oil seal was dripping and was replaced at ~ 70,000miles. I see little value in running a heavier than recommended viscosity. Ed

KCJeep · Mar 30, 2016

The Jeep 4.0 does like a heavier oil, but IMO a 15w40 is overkill. A 30 grade on the thick side or a light 40 grade is more than plenty. If you want a diesel oil, Rotella 10w30 would be a great choice.

Pennzoil HM 10w30 is also thicker than your typical run of the mill 10w30, and the Jeep 4.0 sure does like all that moly in it too.

Nothing wrong with a good 5w30 over the cold months. Even then I favor a "thick for grade" oil like Pennzoil HM. Running that now as my winter blend but it is due to come out May 1st.

artificialist · Mar 30, 2016

The reason some people recommend diesel engine oil for the Jeep 4.0L is the zinc and phosphorous content. Those ingredients are mainly there for low wear in flat lifter camshafts. Most 15w40 is diesel approved.

However, OEM and mild flat lifter cams don't need any extra ZDDP. Regular API oil is fine.

10w30 is probably better than 15w40 in your engine.

If you would like to use HDEO, I would go to Walmart where I can get Chevron Delo 10w30 synblend for under $15 per gallon.

Jeep 4.0 - Valvoline Premium Blue 15w40

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