I think 15w-40 in my jeep was a mistake

I can't see how going up 4-5 cst kv 100 or 0.8-1.1 cst hths can make an engine sluggish especially in summer west coast weather. I went straight from 0w-20 to 5w-40 in my new suv and the engine free revs the same. Doesn't feel like there's thicker in there. Same with the 15w-40 in my old trucks. Maybe you revved it while that 10w-30 was hot and thinned out and the 15w-40 was cold. Maybe there could you see something of a difference. But you can go to 5w-40 next time. Castrol 5w-40 is 23.97 on the walmart shelf right now.
 
i understand it’s a flat tappet engine but HDEO is tailored for diesel motors. M1 0w-40 would be my go-to for a flat tappet motor. leave HDEO where is belongs, in a diesel oil sump. i only top up with it in my oil burning accord because i have 20ish gallons of delo 5w-40 from the advance clearance.
 
Chris142 said:
Seems many people rave about how well 15w40 does in the 4.0 jeep engine.

Mine was due for a change last week so I put 15w40 in it.

I can sure feel a difference. It's very sluggish now.

You wouldn't think going from a 10w30 to a 15w40 would be noticeable but I sure can feel it.
Click to expand...

Rotella 10w30 T5 is a great oil and that would be my choice.
 
Chris142 said:
Seems many people rave about how well 15w40 does in the 4.0 jeep engine.

Mine was due for a change last week so I put 15w40 in it.

I can sure feel a difference. It's very sluggish now.

You wouldn't think going from a 10w30 to a 15w40 would be noticeable but I sure can feel it.
Click to expand...
15W-40 might be great in a Riding Mower that is air-cooled and sees temps near 250F. I have read posts where people went from a 30 Weight Oil to a 40 Weight oil and experienced what you are seeing. My car is specked for 5W-20, and I am now using 5W-30

I think I can feel a slight difference where the 5W-20 was a tad more responsive than the 5W-30, but I am happy with the Higher HTHS Number of the 5W-30
 
Chris142 said:
Seems many people rave about how well 15w40 does in the 4.0 jeep engine.

Mine was due for a change last week so I put 15w40 in it.

I can sure feel a difference. It's very sluggish now.

You wouldn't think going from a 10w30 to a 15w40 would be noticeable but I sure can feel it.
Click to expand...
10w40 & 15w40 are way to thick for a Jeep 4L, IMO. I owned 3 of them. 15w40 is way to thick at cold start and somewhat too thick at full op temp.

5w40 Valvoline or Mobil One Truck & SUV both do well in a 4L.

Pennzoil Ultra Platinum 5w40 is good if you want a 5w40 that's on the thin end of grade. Mobil One for middle of 5w40 grade. If you want a bit thicker, then Valvoline 5w40.

If you want a very thick 5w40 then any brand of Euro 5w40, but that might be thicker than ideal.

Another good option would be 5w30 Quaker State Ultimate Protection Full Syn or Shell Rotella Multivehicle because those are thick for a 5w30 grade.

Look at data sheets. Compare the stated KV100 cSt viscosity of each of the above oils. I think you'll find that the KV100 cSt viscosity will rank as follows (from lowest to highest):

5w30 (great for 4L if the oil is a brand that's on thick end of grade)
10w30 (obsolete, IMO)
5w40 (thicker than Xw30) (great for 4L, if not a Euro oil. Euro might be a bit too thick)
10w40 (thicker than 5w40) (too thick)
15w40 (by far the thickest) (way to thick)

Anything thicker than 5w40 is too thick for a Jeep 4L, IMO.
 
Last edited:
JavierH19 said:
I can't see how going up 4-5 cst kv 100 or 0.8-1.1 cst hths can make an engine sluggish especially in summer west coast weather. I went straight from 0w-20 to 5w-40 in my new suv and the engine free revs the same. Doesn't feel like there's thicker in there. Same with the 15w-40 in my old trucks. Maybe you revved it while that 10w-30 was hot and thinned out and the 15w-40 was cold. Maybe there could you see something of a difference. But you can go to 5w-40 next time. Castrol 5w-40 is 23.97 on the walmart shelf right now.
Click to expand...
Depends. I could feel in VW EA888 engine every time I bump from XW30 to XW40. So jump of some 0.2-0.3 cP. You can feel the turbo kind of needing a split second more to spool.
In BMW I cannot feel that, in Toyota too. Also could not feel that in my BMW twin-turbo diesel. But in VW with EA888, I could absolutely feel it.
 
Chris142 said:
Seems many people rave about how well 15w40 does in the 4.0 jeep engine.

Mine was due for a change last week so I put 15w40 in it.

I can sure feel a difference. It's very sluggish now.

You wouldn't think going from a 10w30 to a 15w40 would be noticeable but I sure can feel it.
Click to expand...

That was exactly my experience with Delo 15w40. The sweet spot seemed to be a 5w40 or 10w30 HDEO. I did run PYB 10w40 one summer and it was fine but 10w40 conventional tends to shear a lot so probably why.
 
These types of sluggish feeling after switching to thicker oil is really noticeable in low power gas guzzling older engines, like my 2001 Chevy Blazer with the 4.3 vortec that makes 190hp and 250lbft of torque, mated to a 4 speed automatic that does a horrible job at keep you in the power band.

Tried euro 0w40 in my 4.3 vortec for a couple OCI’s, and while I was running the 0w40 for a couple OCI’s, the engine felt normal to me at the time, then I switched to api resource conserving 5w30 that was 10cSt @ 100c, and the difference was very noticeable. With the thin 5w30, the engine and the whole truck just felt peppier, like the weight of the truck dropped by a couple hundred pounds. With the 0w40, it felt like the engine was being lugged, especially when trying to pass a vehicle on the highway.

Try running 0w20 then a 40 or a 50 weight oil on a heavy vehicle that has a low powered engine like the gm 4.3 vortec. You’ll feel it.

But on the other hand, my other vehicle which is a 2010 ford Taurus sho, with the 3.5 Ecoboost. It doesn’t matter what oil I put in, the engines torque makes so much power with the tune I have, and I don’t feel any difference, weather I’m using 5w20, 5w30 or 0w40.
 
BrendanC said:
i understand it’s a flat tappet engine but HDEO is tailored for diesel motors. M1 0w-40 would be my go-to for a flat tappet motor. leave HDEO where is belongs, in a diesel oil sump. i only top up with it in my oil burning accord because i have 20ish gallons of delo 5w-40 from the advance clearance.
Click to expand...
It's a dual rated oil.
 
Chris142 said:
I used it because I had it on hand and didn't have to run out and buy oil.
Click to expand...
fully understand that, i also top up with it in my 400K+ mile accord because i don’t really care if it blows up tomorrow, it has paid for itself in fuel savings many times already. Would just go back with some M1 0w-40 next oci.
 
You must log in or register to reply here.

Similar threads

Carlostrece
Cheapest version Supertech
2
Replies
34
Views
2K
Carlostrece
C
New to Real Winters; One Badly Ticking Lifter on Jeep 4.0L Startup/Don’t Drive Enough For 2x/Year OCI
2
Replies
32
Views
2K
facility1
S
Help me "over think" this as many of us here like to do - Mixing 0W-20 with 15W-50 to achieve close to 5W-30
Replies
18
Views
1K
JimPghPA
W
Feeling the difference, switching to Synthetic (PAO Group IV)
Replies
9
Views
1K
WiredForStereo
M
Could smaller be better?
Replies
17
Views
557
MX/Jeepguy
Back
Top Bottom