I am thinking of switching to synthetic on the Jeep. She doesn't have a lot of miles for her age (96' 116k) but I am just wondering if the higher price of synthetic is worth the switch over?

I live in AZ and I am running 10w40 on it now (will probably switch back down to 10w30 considering it's still pretty cold this time of year) but I am just wondering if there's really any real benefit to switching to synthetic now, or just continue using conventional dino oil.

I use castrol gtx now. I am thinking of switching to valvoline synthetic or even castrol's brand of synthetic oil.

EDIT: Also how many of you have put a quart of ATF in your car when you change the oil, and if anyone wouldn't mind explaining to me how that works. Can I just use any regular ATF, and do I substitute one qt of oil for ATF or do I still add the 6 qts and then add in the ATF?

 

All i run is castrol GTX 10w40 and 10w30 and she still runs like a champ, 160k miles. i've heard that with synthetic it may cause a leak somewhere that the thick oil was preventing because synthetic is really thin oil. but im not for sure. u see jeeps run to 300k miles on regular oil, personally i like Castrol GTX because its not parafin based (SP?) but am thinking about running a oil that has more ZINC in it, our xj's like ZINC.

 

STICK WITH THE DINOSAUR OIL! If you have always run the dinosaur oil and your xj has a good number of miles on it (as Im sure it does) stick with it. The synthetic will make everything leak. I have no idea why but it does. Castrol is a great oil. But definetly dont go to synthetic if you have been running it all along

 

Yes and no. There is a TON of info out there on this subject. I spent quite a bit of time researching this subject,reading posts here and elsewhere, and talking to others, AND...
In a nutshell:

Synthetic is better. Why? Biggest two reasons are better ability to lubricate quickly on startup( for a number of reasons) and better ability to withstand high shear loads and abnormal temperature extremes without breaking down. Also, there is a fair amount of reason to believe that synthetic can be run longer between oil changes...exactly HOW long is somewhat open to interpretation, and some other factors like your oil filter. That having been said, PLENTY of 4.0s go 250-300 thousand miles with dino oil. If you just drive to work and back and change the oil with quality oil filters and dino oil every 3000 already, then stick with it. I run Rotella T 5w-40 full synthetic in my cherokee. It loves it, the 5w really helps the old lifters pump up quick in the cold, also Rotella T has more ZDDP ( stuff that is good for the 4.0's camshaft) than alot of other oils. I think it is cheap insurance,and I feel the synthetic not only protects better but controls sludge better. Some say that it will cause old seals to leak alot beacuse it de-varnishes them so thouroughly...this was not my experience after switching at 100K. Hope that gets you started,good luck,spend some time searching and form you own opinion!

 

I switched to AMSOIL about 5 years ago when my '94 had 98K on the clock. I also use their ATF (noticeable change in shifting) and diff lubes. P/S quited down when I switched also. I was VERY skeptical about the longer intervals between changes but after all these years, I've come to grips with it (mentally). For me, it's about long term reliability. IMHO I think synthetics are for those who want the best for the junk.

 

I was thinking of going for Amsoil too, 10w40 weight. I need to order some gear fluid as well so I figured I might get the oil as well. Online it's about 40 bucks for 6 qts which is a little pricey but if it really is worth the price I'll scrunch it up.

My main concern is if I am not happy with synthetic can I switch back to dino oil or no? I don't think my motor has any sludge build up or is dirty inside as it was fairly well maintained by the original owners.

I don't know, the choices are killing me lol.

 

I switced my 98 XJ to full sythetic at 16500 miles & I use a K&N filter with Valvoline oil, I first used a synthetic blend to see if any leaks came up, but since FS pressure has improved dramaticly upto 50ibs at 2000 rpm & doesn't drop below 15/20 at idle. It can cause oil leaks to increase but gaskets are never a bad investment on an old motor anyway plus my oil changes can go 6000 miles meanin as long as I change it late fall you won't see me under the Jeep no more in the winter even & I run the $h!t out of mine like to play in the snow.

 

I would stick with the OEM recommendations (10w30). Higher viscosity may only be of value if you have some issues already relating to oil thickness.

Short story: I'm a contractor and have a Hitachi air compressor that says to use a 10w50 synthetic. It's always been a pain to use it in the winter because it wouldn't start and would blow the internal circuit braker. So after 3 years of fighting this I switched to AMSOIL and the problem went away. The point is that all synthetics are not equal.

 

What's everyone's opinion on shell rotella oil? Seems like the 4.0's like the rotella stuff, the problem is finding a 10w30 weight.

Any ideas on where to look? Or if this is a bad idea altogether?

 

I am having trouble finding the 10w30 weight on the shell stuff. I have only found the shell rotella synthetic blend stuff but they only sell them in gallons and I need 6 qts total.

What do you guys think, should i give up on my search?

 

buy them in the gallons and measure it out.

 

Found this a really interesting read.
http://www.carbibles.com/engineoil_bible.html
For me it is dino oil for a dino engine, over here the light weight synthetic oils are regarded as necessary for the modern tight tolerance OHC 4 valve engines especially with the turbos.
Our 4.0 ain't a modern engine design by any measure.

 

wouldn't hurt to get two gallons of it. look at it this way: if you develop a leak, the extra oil from the two gallons is already at your disposal to top it off, and never hurts to have some extra fluid in the back anyways. i keep oil, trans fluid, gear oil, and 50/50 antifreeze mix in the back at all times. saved my butt a few times during the summer on roads trips.

when i got my jeep, it had about 75K miles on it, and the first thing i did was switch to synthetic 10w-30. it ran much cleaner, but i did develop a leak. after a few years of learning my jeep inside and out, i found out that the valve cover gaskets on some of the 4.0L like to leak because the rear bolts like to come loose, and the gaskets themselves were thin, cheap strips of rubber. replaced it and haven't had any leak issues since. lots of jeep owners will mistaken that valve cover leak as a rear main seal leak when they switch oils, and most of the time, it's just the bloody valve cover!

 

Well talking with the other mechanics where I work part time, they found when people they talked with that switched to Full Synthetic, their vehicles ended up with leaks. Many moons ago when I owned a 76 CJ-7, I only used Quaker State and when the engine started loosing power, rings were worn on 2 clyinders. The engine builder commented that my jeep had the cleanest oil passages he had ever come across. So the old dino oil works great as long as you change the oil every 3 to 5,000 miles. I used to change it 2x a year. My uncle switched to full Syntic. to see if there would be any difference with mileage etx. and ended up going back to regular oil. He did not see any great increases verses the extra cost. You can find the regular oil and filter for $15-20, but full Synthetic can cost up to $40-50. My 96 XJ has 135,000 and is still running strong with regular oil.

 

Full Syn
Tends to find the smallest hole and leak thru