tvarney26

jw anyone know the pros and cons of running synthetic in a 4.0 and if its a good or bad idea to switch from conventional to synthetic. ive heard its not good for seals to switch but i would like it to run cleaner.

speedballin

If you run synthetic. I think you'll find. A lot of cracks you didn't wanna find, you could prolly run synthetic with Lucas stop leak but at that point might as well run regular

Parsnip

Your motor is designed to run better off conventiomal...that being said its.not out.of the question to run synthetic however the switch in process is extremely costly, requiring several oil changes from mixed blends all the way to Full synthetic...its not worth the time imho, you wont run any cleaner or dirtier then now

hankthetank

synventional lol...run whatever makes you sleep better. pretty sure latest synth has seal conditioners to prevent leakage. bobistheoilguy <<<google that.

Sails

I run full synthetic in all my vehicles, we tend to be higher mileage drivers and my 2001 XJ 4.0 is a DD.
Oil change timing that comes around isn’t always convenient and the synthetic doesn’t break down as fast as conventional so it gives me a cushion to get the change done. Peace of mind anyways. Also could be a couple of more mpgs due to it.
As to leaks, haven’t had any yet and don’t expect any due to the synthetic oil but then my XJ only has about 42,000 miles on it.

SoCalxJ4.0

Doesn't sound like high mileage driving. Lol

I was told by multiple engine guys to stay away from syn. In a 4.0. So I do. I change my oil around 5-7k miles, and it's never dirty, and never had a leak since she was new in '96.

MarkF

I don't agree changing to synthetic will cause leaks. I used to sell automotive chemicals so I had to know a lot about oils and additives, and I've had a lot of personal experience with synthetic oils every since Mobil1 first hit the market. I tried it on a new car (only 3,000 mi) and it went through a quart every 500 miles @$5/qt when conventional was $.79/qt. But after going back to conventional until going back to Mobil1 after 12,000 miles it didn't go through any more than the conventional. But even Mobil1 has come a long way since then.

Getting back to my belief about switching to synthetics...
Over the last ten years I bought 8 used vehicles with between 120K and 200K miles
and switched every one of them to synthetic with no issues at all. The ones I bought that had leaks to begin did NOT get worse and a Pathfinder with 155K actually leaked less. Of the vehicles with no leaks, none started leaking.

If by chance you even change brand of oil (whether conventional or synthetic) and you start getting leaks, it's not the fault of the oil, but most likely a higher detergent oil that may have dissolved old varnish on the seals and thus allows leaks. In those cases, the seal was already shot and the varnish was doing the sealing.

In the end I say if you have a leaker, fix it but don't blame it on the oil. If anything blame it on the previous owner for not changing the oil enough (or using P****oil... oops!) and allowing the crap to build up.

At least that's my opinion based on years of first-hand experience...

Sails

I have had it for about 6 weeks and started with about 39,000 and has been under going floor reconstruction and a bunch of other upgrades. Last year my Santa Fe did about 48,000 miles and the XJ will be replacing it. My wife did 36,000 on her Camry so I think that the 84,000 between us may not be the highest but it beats the 12,000/24,000 considered as normal.

SoCalxJ4.0

I hear ya, just giving you a hard time

Sails

With good reason! 42K on a 01 ain't very much!

tvarney26

anybody running 15w 40 rotella t triple action

RTorrez1

This is what I run in my 98. Along with a good quality filter. Such as Wix, Mopar. What ever you do. DO NOT use fram filters on you 4.0 Jeep.

cleenrob

Why not a 10W 30 rotella isnt that what viscosity is recomended to use?

RTorrez1

Why not 15w 40?
But really the only reason I went with the 15w 40 was when I bought it the were out of 10w 30. Plus they had the 15w 40 on sale for $12.95 for the large bottle and it is normally $18 or $19.

Radi

If you like it, run it. If you decide you don't like it, switch back. There is no complicated process to switch from conventional to synth and back. Many "synth" oils are just highly processed conventional oil anyway, lol.

If you stick to a 3k-4K change interval, I personally don't see the advantage to a synthetic, but that's just me. It certainly won't harm anything, it's just costly.