TrekkerJmm

whats the best weight oil to use in a high mileage 4.0?...Tj

fivendime

Aww, a question with no right answer. The problem here is that each person loves a different weight and a different brand and whether it has a synthetic blend or a full synthetic or just plain old oil. It also depends on the weather, if its really cold for a long time like months and months you'll want to run a thinner viscosity oil. If its hot a thicker viscosity oil. I can tell you what I use though. The standard Valvoline 10w30. The weather stays mild here in Washington state for most of the year so I can get away with it.

TrekkerJmm

Thanks for the reply, I usually use 10/30 in the winter and 10/40 in the summer myself. Was just wondering what everyone else uses, Thanks...Tj

whowey

As long as you are running a good quality API-SL rated oil your engine is going to be happy.

Weight is going to depend on location and your prevailing weather.

Remember when looking at a multi-viscosity oil the first number is the effective viscosity at 0 degrees.. the second the effective viscosity at operating temps.

fivendime

YES!!! I forgot about mentioning that. Amsoil is what my dad puts in his cherokee.

funkle95xj

I use Mobil 1 10W-30 High Mileage in my XJ. Every 3K on the dot, and I always use a new Mopar oil filter every change too. Makes for a happy 4.0L!

littleblueman

As i have for years i stick with Valvoline 10w-30. Ive used the high mileage blends in the same weight, but i cant see a difference. Change that oil every 3k and add a new filter (I use the Motorcraft FL1A) and you'll keep her purring and happy.

michigan_maniac1987

i work at a shop and have tried just about everything from mobile 1, hight mileage, slick 50, 10w30, 5w30,...ect the best that i have found for a high mileage engine was 15w40 rotella T, its used in diesels, its thicker, i found out if you have any leaks(even small ones) synthetic oil will tend to leak faster because the molecules are bunched closer together, synthetic will also drain faster from you valvetrain than thicker oil, thus more noise and wear on cold starts..just my 2 cents

claygrassmann

i use 5w30 in the winter and 10w30 in the summer but i also live in upstate ny

BuckB91XJ

My XJs 4.0 has 240K so I use 10W-40 get get a little more thickness. I also use a high mileage oil. Usually Castrol High Mileage.

XJ Stryker

Rotella 15/40 FTW! Nothing beats a good diesel oil.

athenscj5

So what is the difference in a diesel oil and others. I like the idea of a thicker oil for my XJ 4.0. There seems to be some ticking in the valves and I think maybe an oil thicker than 10W30 would help that.

98 JeepJeep

the diesel oil uses more Zinc........Your probally hearing the famous LIFTER Tap most of the AMC 4.0's Suffer from...(mine included) I run 10W40 Penz High milage.

XJ Stryker

EEEWwwwww get rid of the PEnz, Jeeps hate pennzoil.

Yes the rotella is one of the few oils that still has HIGH Zinc and other stuff that keeps your engine running bettter.

Great on older High mileage vehicles.

can'tstopjeepen

I used the rotella 15/40 in my f-350. So you guys that use it in your 4.0's there hasn't been any problems with it. I'll try it if it works for you guys. We are all running the same motors here. I have about 147,000 on that zj I just got.