Time to change my oil.

[Jaime]

It is time to change the oil in my MJ and WJ. I was thinking of changing from conventional oil to full synthetic. I usually use Pennzoil as I can get it at a lower price at the base. What do you think? Also what weight should I use in synthetic?

[omega_rugal]

it can run on good old mineral, synthetic can last longer but the 4.0 is a dirty engine, it will turn it into black goo very soon, as for the weight depends on its health, does it burn oil right now?

[Jaime]

Not really about 1/2 a quart to 3/4 of a per oil change.

[Chad R]

      I have run synthetic in my 01 wrangler since it was new I run 10w40 mobile1 no problems at all. 
      If I were you I would not change. If you have higher miles on the WJ it will probably start leaking more oil than it does now. On the Mj keep what you are doing and add zinc additives to the oil or switch to high mileage oil or diesel oil. You need the additives in the oil because of the lifters.

  Oil manufacturers took out some of the additives because newer car run roller lifters and don’t need zinc and other additives in it any more. From what I have been told that you can wipe out a cam with today’s oils in pre 95 cars. We run 15w40 Mobil delvac in our classic cars from our 49 jeepster to our 69 396 camaro.

    But do what you want, do the research And make a decision that works best for you

[WahooSteeler]

Oil is always a hotly debated topic, lots of opinions LOL.

 

I'm no expert or engineer, I'm only going to regurgitate what is often pointed out here on CC and that is that Rotella T6 synthetic is generally considered the best for the 4.0. Some time ago a member posted a study/report from somewhere with a wiiide range of oils, everything from Walmart brand oil to Royal Purple, Red Line etc. There was a spreadsheet containing the amount of all of the additives in each of the oils and the best "blend" for the Jeep 4.0 was found in Rotella T6. I may not be correct, but IIRC there was some science and engineering behind the report and not just someone's opinion. I don't believe the study/report was done specifically to find the best oil for Jeep 4.0s, but again, it's been awhile since that was posted. T6 is also now available in 15w-40 so I would assume that may be better for you in Nevada than the more common 5w-40. And it's cheaper than Mobil 1 and other synthetics, so even better. 

[watchamakalit]

I personally am not sold on the "added benefits" that are associated with synthetics.  I have tried them in a few different engines over the years and was never real impressed.  It seems you can take an engine that is healthy and doing well on dead dinosaurs and by simply changing the oil to synthetic, you can create alot of leaks and additional sledge build up on the internals.  That said I run Rotella T4 with is the conventional version of the aforementioned T6.  It seems to keep things a bit cleaner and my engines don't seem to use/lose as much oil between changes. 

 

I would also like to add that this is all based on my personal observations over time and your mileage may vary.  Its just an opinion, and we all know what those are like.....

[Jaime]

Thanks everyone.

Looks like I’ll keep using conventional oil if synthetic might create leaks. 

[omega_rugal]

for a 30 year old engine thta was designed like 50 years ago, going syntetic makes little difference

[75sv1]

I use Rotella T6 5W-40 presently. I did replace all the seals though. I had used Rotella T-4 10W-30 conventional.