Jeep Question

[ARMY_Guy]

Hello.
Many on this forum have said the Jeep 4.o engine loves a thicker 5w4o oil; like my TDT. Why? Why do some vehicles perform better with particular oils??

-A

 

[Bryanccfshr]

That's just a bumch of scuttlebutt. The fact is that the 4.0 is a durable engine and is not particular about engine oil so long as it meets the specs.

 

[ThirdeYe]

I've known people that have used nothing but 10W-30 and gotten hundreds of thousands of miles out of the 4.0.

 

[MarkC]

QFT

 

[Gary Allan]

Yeah, the engine really isn't picky. Some UOA's produced higher Fe readings than the same engines using heavier oils. Plenty of people got very respectable Fe readings with simple 10w-30 ..but it was a YMMV kinda thing. I know my wife's 4.0 did terrible with M1 0w-30 and cut the Fe by like 50% (iirc) by going to Delvac 1 5w-40. If it's a morphed myth, it's got decent incidental support.

I will say that I've seen no difference in any perceivable way between 10w-30, 5w-30, 5w-40, and 15w-40 over the winter. No fuel economy difference ..no added noise..no problems cranking.

The 2.5 isn't quite the same. You can tell the cranking with heavier oils in colder weather, but that could just be the starter that they gave it.

Basically I think it breaks down that it's one of the few engines that can actually take advantage of HDEO's and heavier oils. Most contemporary engines just can't. It is kinda a dinosaur. It's a tough engine, so most match it with a tough oil.

It just wouldn't feel right putting something like M1 0w-40 in the thing.

 

[pavelow]

2.5 is just a sawed off 4.0-the 4.0 is based upon the 2.5. Rotella 5W40 will work just fine in the 2.5-the 2.5 works much harder than the 4.0 and could use the extra protection of a HD oil.

 

[Gary Allan]

Yes, indeed the engine is a hacked 4.2 with a better head ..that the 4.0 got later ..and YES, 5w-40 performs well in it as it does the 4.0 ..

..but that doesn't alter the fact that the 2.5 shows cranking stress with heavier oils in subfreezing temps where the 4.0 did not

 

[Nick R]

2.5 isn't exactly the 4.0. It's the same block, but it's bored out more than the 4.0L is. My dad runs M1 10W-30 in the 2.5 in the jeep, it seems to run fine to us.

 

[Gary Allan]

Same bore, shorter stroke. 3.88 bore for both. 3.19 vs. 3.413

Probably the origins of the heavier thing is that the owners manuals all allowed 5w-30 ..but had a PREFERRED after 10w-30. They also advised using 10w-30 if sustained high speed use in 90F ambient temps would be expected during the OCI. I think this was a carry over from shear prone 5w-30.

 

[Zaedock]

Originally Posted By: Gary Allan
..but that doesn't alter the fact that the 2.5 shows cranking stress with heavier oils in subfreezing temps where the 4.0 did not

The only time mine starts slower is when I leave the tranny in neutral and she has to crank a gallon of cold gear oil too.

 

[addyguy]

I think the idea that thse engines preferred thicker oils comes from the old AMC days - in the 1970's, recommended oils for their engines were 10W-30 or 10W-40, or straight 30 or 40....most ran for many, many miles on that, and the engine hasn't changed much....so many probably thought the oils shouldn't, either!

 

[ryan2022]

Not sure about the 40 weight, but in the life (long life) of your engine, you probably wont notice a difference between the 30 and 40 weights.

I'm sticking with a 30 weight, due to avoiding the extra strain on the oil pump that a thicker oil might cause, as well as reduced fuel economy.

 

[SecondMonkey]

For the Jeep 4.0 I always lean toward 40w at 225,000 miles. Still runs like new, and has an amazing amount of original parts. Under 100k, I'd say 30w is better.

You can probably run anything from the cheapest straight 30 oil to the most expensive 20w50 oil, if changed often enough, your 4.0 should hit 300k easy. 400k probably. 500k maybe.

Slightly OT, anybody know if you can bore/stoke a 2.5L engine? Been thinking about building a super high MPG Jeep with reasonable power...

 

[Zaedock]

Originally Posted By: SecondMonkey
Slightly OT, anybody know if you can bore/stoke a 2.5L engine? Been thinking about building a super high MPG Jeep with reasonable power...


You can slightly bore the cylinder, but there is no way to stroke it without a custom crank. It would be much, MUCH, cheaper to super/turbo charge. There are other cams that you can stick in if staying N/A, but they will change the powerband of the engine and more than likely kill some of the lower end torque. IMO, the factory did a decent job with the way the engine is. It has decent low end grunt for trail duty. Most people who run 2.5L's (including myself) just live with the streetability difficulties when running larger tires.

The best way to get a better (note: not super) MPG Jeep with reasonable power is to go diesel, and then you are still driving an aerodynamic brick with wheels. A GM LS series engine swap would probably give better mileage than either the 2.5L or 4.0L factory engine.

 

[OAS]

Originally Posted By: Gary Allan
Yeah, the engine really isn't picky.

I will say that I've seen no difference in any perceivable way between 10w-30, 5w-30, 5w-40, and 15w-40 over the winter. No fuel economy difference ..no added noise..no problems cranking.


Good to know.
Ive been using PP 10-30 in my '97 Cherokee, but have been thinking (since its got 121,000 on the clock now) that maybe RTS 5-40 or Maxlife 10-40 might be more appropriate.
Although i think the PP is a bit cheaper than RTS at wally's? (nbd anyways)

 

[artificialist]

Originally Posted By: Gary Allan
Same bore, shorter stroke. 3.88 bore for both. 3.19 vs. 3.413

Probably the origins of the heavier thing is that the owners manuals all allowed 5w-30 ..but had a PREFERRED after 10w-30. They also advised using 10w-30 if sustained high speed use in 90F ambient temps would be expected during the OCI. I think this was a carry over from shear prone 5w-30.

I saw a manual for a Jeep Grand Cherokee from the 1990s, and while it said 10w30 was preferred for the 4.0L, it also said 5w30 was preferred for the 5.2 for some reason.

I heard it is because the 5.2 has roller lifters and the 4.0 doesn't, but I am not sure if that is the reason for the different viscosity recommendations.

 

[Gary Allan]

That would make sense. Amsoil doesn't appear to distinguish recommendations between the 4.0 and the 5.2. They may not have that one right ..but they're usually pretty good. I ranged from 94-98
Engine Oil
Grade 1......API*
Signature Series 0W-30 100% Synthetic Motor Oil (SSOQT)
SAE 10W-30 Synthetic Motor Oil (ATMQT)
XL 10W-30 Synthetic Motor Oil (XLTQT)
Above 0F......10W-30
Below 61F......5W-30

Now for the 4.7 they do have some qualifiers

Engine Oil
Grade 1......API*
Signature Series 0W-30 100% Synthetic Motor Oil (SSOQT)
SAE 10W-30 Synthetic Motor Oil (ATMQT)
XL 10W-30 Synthetic Motor Oil (XLTQT)
Above 0F......10W-30
Below 100F......5W-30

 

[SecondMonkey]

I remember my old manual for my 1990 Cherokee with the 4.0 said basically to use 10w30 for cold weather/light duty, and 10w40 for warmer weather and things like towing. (This manual was mostly written by AMC with some chrysler logos printed on top)

My 1996 Cherokee, with the SAME body, and the SAME engine...but a Chrysler manual...recommends nothing higher than 10w30. The only thing that changed in between is EPA requirements...and the intake manifold.

 

[Gary Allan]

Yes, in the 70's it was up to 20w-50 ..straight 30 ..10w-40

 

[Durango]

SecondMonkey,

If fuel economy is your game I'd try the Chrysler new standard oil specs of 5W-20 oils. I admit my second car/truck 01 Dodge Durango wants 5W-30 so that what I use all year but then I don't live in Oregon so your climate is much different. I heard it rains allot.

Now a days 5W-30 is considered the new national standard of oils compared to the old days where more people use 10W-30 during those late times where 10W's were considered the national standard.

Good luck and have a nice remander of the holidays.

Durango