Recently got a used 93 XJ with a little over 200k on the clock with the 4.0 HI. The PO told me that he has been using 20w50 Castrol, which seems a little thick for this tired I6. Today I noticed that sitting at a stop it will smoke a little and you can smell the oil with the windows down. Nothing too bad, but I'd like to hear some opinions on what would be a good choice of oil (weight) to run. I live in NC, so we have fairly hot summers- usually in the 90's and mild winters. I plan on changing the oil tomorrow and would like to pick up the right weight stuff at the Napa. 15w40 Diesel, 10w40 Castrol? Any suggestions?

 

in my owners manual it says 10w30 is preferred. i usually use a synthetic, its more expensive but its way better with the high milage
and i dont think it would be smoking from that weight of oil. did you check to see if it was leaking possibly?

 

I have been keeping an eye out for leaks, my cardboard that I stick under it is still dry...
I kinda am one of those non-synthetics guys, mostly because of the cost and being old school I have never ran it-always just ran Valvoline or Castrol. Is 10w30 what most of you guys with high mileage 4.0's tend to run?

 

5W30 probably wasn't available when the manual was first printed but would be preferred over 10W30. At normal operating temp they are the same weight but 5W30 will flow quicker to engine parts when below normal operating temp.

 

My manual has both 5w30 and 10w30, and states 10w30 is preferred. 5w30 is for temps below freezing. For that hotter climate you describe, both the 10w30 and 10w40 should be fine. I'd run 10w40 and see how noisy the engine is and watch for oil consumption. If he was running 20w50 there might have been a reason. 10w40 is about the thickest I would go for a 4.0L, since it was recommended in the manual in the late 80's and early 90's for hotter climates. 20w50 is pretty thick stuff though.

 

10w30 valvoline maxlife is what i run in mine. Same as the other poster, owners manual in mine states that 10w30 is preferred for the higher temps and 5w is for the colder temps. Hope this helps.

 

Go to a lighter oil 5 or 10/30. Then check compression. my guess is the PO avoided doing a ring job by running heavy oil.

 

I'd be willing to bet that if a 10+ year old owners manual was re-written today, it would say 5W30 is preferred. Most mfgs. manuals today recommend 0WXX motor oil. 5W30 will always flow quicker to engine parts than 10W30 at any temp below normal operating temp, including freezing ambient temps. At normal operating temp both 5W30 and 10W30 flow the same but the fact remains that more engine wear occurs at below normal operating temps. 100F oil/coolant temp is well below normal operating temp and it's also well above freezing but 5W30 will flow better/quicker at 100F than 10W30.

http://www.supramania.com/aehaas/

 

Thanks for the advice. Do you guys think I will opening a can of worms switching to 10w30 from 20w50 with this high of mileage? I mean I don't want it to start using oil or smoking more than it is right now because it is manageable as it is.

 

My concern would be that the heavy oil is masking a major problem that may strand you on the side of the road or worse on the trail. Blown motor sucks on the freeway, but it really sucks 20 miles from the nearest road.

 

hmmmm....well hopefully that problem if it exists, will continue to hide from me. So I guess I should stick with 20w50 from now on, or at least as long as I run this old 4.0, right? Wouldn't compromise the longevity of the motor's internals? She won't be seeing high rev's or any extreme use, just mostly daily driving and light trail/mud

 

Stick with the 20W50. It will give you more engine life and less bearing wear under hard use. Take a lesson from the guys that race. That light oil is to boost the milage ratings for the EPA and for use by soccer moms

I use it and like it

 

Heavy oil in a motor that calls for 10w30,if its a dd i would run what it calls for.If you need a bandaid for the motor run 20w 50 , 15w40 etc or its just for off road.No real reason to run such heavy oil in a dd.

 

..........and just re-build/replace your engine every 500 miles or after every race, which ever comes 1st. Last time I looked, the NASCAR dudes were using 0W motor oil during time trials.

 

I was thinking of something more local, like the sprint cars. They race every Friday night for months. Those other guys have unlimited budgets and are not running anything that can be compared to what we have.