Yup. 4.0L
I think 15w-40 in my jeep was a mistake
- Thread starter Chris142
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You had the wrong dipstick, wrong tube or a smashed oil pan. Every 4.0 holds 6 regardless of year or what it's in
I can most definitely feel the difference between 0W-20 and 5W-30 in my Civic 1.5T engine. Particularly when cold. Mind you, a cold start in my area is maybe 60F in the morning, but still...
Is it also sluggish when the 10W-30 is cold?
I have seen 4.0 Jeeps with over 1/2 million miles on them on synthetic 5w30. Why in the world would anyone deviate from that? It is, after all, the manufacturers recommendation. I´m sure the manual probably said 10w30 was ok in warmer climates, too.
Nobody EVER ran a 4.0 at the track, so I´m not sure why some folks think a 40 weight would be good for that engine.
OP, if it were mine, I´d just swap it right out for some Mobil 1 5w30 and rest easy as the miles roll by.
Nobody EVER ran a 4.0 at the track, so I´m not sure why some folks think a 40 weight would be good for that engine.
OP, if it were mine, I´d just swap it right out for some Mobil 1 5w30 and rest easy as the miles roll by.
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Add me to the list of BITOGs that have experienced that sluggish feeling when stepping up a grade. It's 100% noticeable in my vehicles.
No you got me thinking of blending some of my 15w40 with some 0w20 and 0w30
Carlostrece
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HDEO made for gas and diesel engines would be ideal in a Jeep 4L if it was a 10w30, or ideally 5w30, such Rotella 5w30 Multivehicle.
The problem with the HDEO the OP used is that it's 15w40.
Also, any non Euro 5w40 that's made for gas engines would be fine.
I would avoid 5w40 HDEO for diesel and 5w40 Euro because they're too thick for a Jeep 4L. I would avoid 15w40 like the plague. 15w40 is unhealthy at startup, especially on a cold morning.
The problem with the HDEO the OP used is that it's 15w40.
Also, any non Euro 5w40 that's made for gas engines would be fine.
I would avoid 5w40 HDEO for diesel and 5w40 Euro because they're too thick for a Jeep 4L. I would avoid 15w40 like the plague. 15w40 is unhealthy at startup, especially on a cold morning.
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Carlostrece
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Earlier someone recommended Mobil One 5w30 for the Jeep 4L. I respectfully disagree. I used to use M1 10w30 in my Jeep and it gave lower oil pressure at idle than I liked. M1 10w30 is thin. M1 5w30 is probably even thinner.
Pennzoil Ultra Platinum is even thinner than Mobil One. I had low oil pressure using PUP 5w40. It was thinner than a thick 5w30. Don't believe me? Try it.
A thick 5w30 will work well. Here are the thickest good 5w30 that I know of.
In order from thickest to thinnest, but even the thinnest on my list is somewhat thick.
Shell Rotella Multivehicle 5w30
Quaker State Ultimate Protection Full Synthetic 5w30
Castrol Edge 10w30 (is in reality a thick 5w30)
Various brands of Euro 5w30 would also be thick for grade and good oils. I don't know where the Euro oils should rank on my list in regard to viscosity. However, Euro oils are expensive an unnecessary for a Jeep 4L.
If not a 5w30, then I'd use a thin to medium 5w40 (i.e. - not a diesel or Euro 5w40)
A thin 5w40 is similar viscosity as a thick 5w30.
Listed from thinnest to thickest I'd use:
Pennzoil Ultra Platinum 5w40 (is thinner than a thick 5w30. Probably too thin, but you could try it)
Valvoline 5w40 (worked well in my 4L)
Mobil One Truck & SUV (worked well for in my 4L)
I'm not sure if M1 T&SUV fits in before or after Valvoline for thickness, but both of those worked well in my 4L.
Undoubtedly there are other appropriate good oils for a Jeep. Those are the ones that I know of and would use in a Jeep 4L. I owned 3 Jeeps with 4L. I suggest using whichever oil on my recommended 5w30 or 5w40 list is the lowest price. Your Jeep will be happy with any of them.
I do not recommend PUP, M1, or Castrol Edge 5w30 for a Jeep 4L because I know for a fact those are thinner than ideal for a 4L. I don't recommend Castrol GTX (in any viscosity) because it's not a good oil and doesn't flow well at cold start.
A friend of mine had a Jeep 4L that went 410K miles (without a rebuild) using basic Supertec 10w30. It's an OK oil. Thinner than I'd prefer for a 4L at op temp, but his Jeep lasted long enough. I suspect it might have lasted 500K+ if he had used a better oil, but who can argue with 410K on cheap thin oil? I don't think he'd have got anywhere near 410K using an overly thick oil such as 10w40 or 15w40 because the cold start wear would be much higher using an overly thick oil.
I briefly tried 10w40 in one of my Jeeps and the cold start noises made me cringe. I soon switched back to 10w30. That was in the days before 5w30 oils were as good as they are now.
Pennzoil Ultra Platinum is even thinner than Mobil One. I had low oil pressure using PUP 5w40. It was thinner than a thick 5w30. Don't believe me? Try it.
A thick 5w30 will work well. Here are the thickest good 5w30 that I know of.
In order from thickest to thinnest, but even the thinnest on my list is somewhat thick.
Shell Rotella Multivehicle 5w30
Quaker State Ultimate Protection Full Synthetic 5w30
Castrol Edge 10w30 (is in reality a thick 5w30)
Various brands of Euro 5w30 would also be thick for grade and good oils. I don't know where the Euro oils should rank on my list in regard to viscosity. However, Euro oils are expensive an unnecessary for a Jeep 4L.
If not a 5w30, then I'd use a thin to medium 5w40 (i.e. - not a diesel or Euro 5w40)
A thin 5w40 is similar viscosity as a thick 5w30.
Listed from thinnest to thickest I'd use:
Pennzoil Ultra Platinum 5w40 (is thinner than a thick 5w30. Probably too thin, but you could try it)
Valvoline 5w40 (worked well in my 4L)
Mobil One Truck & SUV (worked well for in my 4L)
I'm not sure if M1 T&SUV fits in before or after Valvoline for thickness, but both of those worked well in my 4L.
Undoubtedly there are other appropriate good oils for a Jeep. Those are the ones that I know of and would use in a Jeep 4L. I owned 3 Jeeps with 4L. I suggest using whichever oil on my recommended 5w30 or 5w40 list is the lowest price. Your Jeep will be happy with any of them.
I do not recommend PUP, M1, or Castrol Edge 5w30 for a Jeep 4L because I know for a fact those are thinner than ideal for a 4L. I don't recommend Castrol GTX (in any viscosity) because it's not a good oil and doesn't flow well at cold start.
A friend of mine had a Jeep 4L that went 410K miles (without a rebuild) using basic Supertec 10w30. It's an OK oil. Thinner than I'd prefer for a 4L at op temp, but his Jeep lasted long enough. I suspect it might have lasted 500K+ if he had used a better oil, but who can argue with 410K on cheap thin oil? I don't think he'd have got anywhere near 410K using an overly thick oil such as 10w40 or 15w40 because the cold start wear would be much higher using an overly thick oil.
I briefly tried 10w40 in one of my Jeeps and the cold start noises made me cringe. I soon switched back to 10w30. That was in the days before 5w30 oils were as good as they are now.
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I have never been in a 4.0 powered vehicle that wasn't sluggish until it was put in low range. I have owned 3 WJs with the 4.0. Every time they got 15w-40 on the first change and every other, and could tell no difference from whatever was in there. These things get hot under the hood. If I lived somewhere cold I might use something else to keep the oil pump shaft from snapping.
I’m running 25w40 full marine synthetic in a 2010 Cobalt with extreme fuel dillusion for summer use.
Just a lot quieter is the only thing I notice
Just a lot quieter is the only thing I notice
10w30 is the factory recommend weight for any temp above 0 deg F (that's from my 01' WJ owners manual). All this is overthinking on these. They aren't picky. If there is a consideration to oil it should be for oil pressure and what weight works best in that regard as they are somewhat known poor oil pressure over time. My 30k mile 4.0L has seen 3 oils: Quaker State full synthetic 10w30 for the first 600 miles, followed by Rotella T6 10w30 for a good 20k miles and I finally settled on Castrol Euro 5w30 mainly for the A3/B4 HTHS 3.5 minimum because it's suitable for ALL our vehicles (a VW 2.5L Jetta, the Jeep and a 1rst gen Nissan Titan 5.6L with 215k miles).
WHATEVER you do only two things happen with the 4.0L at this point: A) it's going to run forever or B) somewhere between 200-300k miles, usually right down the middle @ around 250k miles a piston skirt is going to fatigue, crack and fail REGARDLESS of what oil and how well you treated it. The other few problems like the run of poorly casted heads that cracked should all be weeded out by now 21+ years minimum later.
I ran ST 15w-40 synthetic in my 4.0 XJ. Never noticed a problem and it ran fine.
In my TJ 4.0 I'm currently running Valvoline Synthetic HM 10w-30. Runs great. The engine is quiet. I'll probably stick with it.
In my TJ 4.0 I'm currently running Valvoline Synthetic HM 10w-30. Runs great. The engine is quiet. I'll probably stick with it.
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Doesn't this completely depend on what "cold" is defined as? I agree with you if we're talking -10 degrees F cold start, but for summertime "cold" starts in most places, wouldn't this be totally fine? Tons of diesel engines are running 15W oils every day of the year in all areas of the country just fine.
Not that I noticed
My owners manual says 10w30 down to 0F and not to use 5w30 over 32f.
Placebo effect is a real thing.
Carlostrece
$100 Site Donor 2025
A Jeep 4L isn't a diesel engine. If you want a thicker oil for it then use a thick per grade 5w30 syn or a 5w40 syn. I belonged to a Jeep club. We did offroading. 5w40 syn and thick for the grade 5w30 syn were commonly used in Jeep 4L and 4.6L strokers with good success in a wide variety of climates on & off road.
A Jeep stroker engine builder told me he'd prefer people use 5w30 in the 4L & 4.6L strokers he builds.
15w40 isn't needed for summer anywhere. If you're worried about summer heat use 5w40 syn or a thick for grade 5w30 syn.
That said, if you live somewhere with hot summers. 15w40 could work, but so would 5w40 or a thick 5w30. 15w40 would not be better, even on a hot day. If an unexpected cold spell comes along, 5w40 has you covered. 5w40 is good year round in any climate for 4L.
Let me put that another way. There's nothing that 15w40 (conv) can do that 5w40 (syn) or a thick 5w30 (syn) can't do as good or better in hot weather. In moderate weather (or at night) 5w40 or thick 5w30 is better at cold start. In cold weather 5w40 or thick 5w30 is good. In cold weather 15w40 is bad, especially for a gas engine.
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Carlostrece
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I think you're reading or interpreting it wrong. In any case, your owners manual oil recommendations are decades obsolete. 5w30 oils have gotten much better. You could run a modern 5w30 syn year round just fine, especially if it's a 5w30 that is on the thick end of 30 grade.
Examples:
Quaker State Ultimate Protection 5w30 (thick for a 30).
Castrol Edge 10w30 (thicker for a 30).
Shell Rotella Multivehicle 5w30 (thickest for a 30).
Otherwise use a 5w40 syn (but not a Euro oil nor diesel oil).
P.S. - A friend of mine owned a Jeep that I sold him at 93K miles. He drove it to 410K miles (no rebuild) using Supertech syn 5w30, which is much thinner than the 5w30s I recommended. He drove it all over Nevada, Arizona, and California for 14 years until he reached 410K miles. Clearly modern 5w30 is fine in a 4L, even in hot weather, even using a cheap thin 5w30 oil.
The excellent syn 5w30 oils I recommended to you are thicker, more robust, and better than Supertech 5w30. The 5w40 syns are also more excellent than Supertech 5w30.
Even so, ST 5w30 was good enough to go 410K miles in a hot climate. So what are you worried about? You don't need 15w40. Furthermore, 15w40 is a terrible idea because it won't always be a hot day. Cold snaps happen. Night time happens.
Use 15w40 if you want, but you'll be doing your 4L engine no favors, especially at cold start on any day that's not hot, or cold starts in early morning or at night.
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