Sooo ive herd running full synthetic in ur jeep can cuase leaks. i have a 98 cherokee with around 170k with a rebuild head, new gasket and injectors. i just bought it about a mounth ago and idk what oil has been ran in it over its life. i currently have 10w 30 quaker states full synthetic ( which i found out it ****ty oil too) so i wanna change it soon and idk if i should run synthetic or conventional. Help Please and Thanks

 

Every one will have a different opinion. But ill start with a fact. Oil dosnt cause leaks! Syn. Is thinner so it will seep through a smaller spot quicker. But rest assured that gaskit was junk already

I run mobil high mileage caues it has more zink and phosphorus witch a I6 needs for a healthy long life. That's in my dd I also run a mopar filter. In my trail rig I run amsoil.

Whatever oil you run just make shur it has extra zink and phos. I run 10w in the summer and 5w in the winter. You can run eather that's just the way I do it.

 

My 2.5 loves the 10W30 QS synthetic. How many miles do you have on the oil and have you noticed any new leaks? What filter is on there? Like brutalxj said, oil doesn't cause leaks. I would play out that fill and see how it does. In my opinion, the only substantial benefit of synthetic is extended drain intervals. So just decide how frequently you want to change the oil.

 

I use Castrol GTX High Milage and its great in my 200000+ mile daily driver. I would only use full synthetic in a newer or just rebuilt engine(under 100000 miles), especially durring break in. I also use a 25% mixture of Lucas Oil Stabilizer. If youre gonna switch oil brands and and or go from regular to synthetic, I would highly recomend doing an engine flush.
Just my 2 cents though...

 

I use 10 w40 valvoline Max life synth/blend with one quart of lucas oil stabilizer. Seems to work pretty good.

 

15-40 Rotella when the temperature is warm and 10-30 Pennzoil in the winter. '88 XJ 230,000.

 

With 170K on your motor, I wouldn't run synthetic unless that's what's been run through it before you got it. It loosens up all the gunk around your 12 year old seals which will cause a leak. My buddy put synthetic through his Yota with only 100K on it and it ended up leaking from the oil pan gasket anyway. He just changed back to conventional and added some Lucas, but didn't work at first. He had to crank the oil pan bolts a little tighter to stop the leak. I would just stick with conventional.

 

Rotella 30w. Stay away from synthectics. Syn oil runs hotter and you do not want that in a 4.0 XJ. it brings the temp up 10 degrees

 

And it deteriorates the bearings.

 

A semi synthetic is good, which castrol GTX HIGH MILEAGE is supposed to be, I'm using 10-40 cause my oil pressure was low with 10-30, now it stays between 20-30 driving. Anyone know if castrol gtx high miliege has good zinc and phosphorus levels?

 

I've used the Castrol GTX High-Mileage in all my vehicles for years now, and I've been quite happy with the results.

 

look it up on their websit but I would say they do. Valvoline High Mileage Synth/Blend has Zinc and Phosphorus in it. I would say most oils have some in it, and most good oils have about the same levels.... the EPA regulates how much can be used due to emissions controls so if someone tells you that their oil has more than your oil... look it up.

 

A lot of people are going to have opinions on this subject and some will tell you not to use synthetic oil, only use conventional 10 w30 etc... dont use lucas... because of some crack pot named bobtheoilguy whatever. Try first to find out what the prior owner was using. I took mine to an oil change shop when i first got it and they told me the last record of oil was synthetic... and based on the opinions of people online I insisted they use 10 w30 conventional. Well my jeep ran like total crap for about a month before I couldnt take it any longer and switched to a 10 w40 blend with lucas stabilizer. I am not telling you to do this I am just telling you what has worked for me so far. If the po ran nothing but 10 w30 ever then stick with it, but if they have been using synthetic then you should probably stay with that. But it is in your best interest to try and find out what that jeep has been using.

 

I had a brand new motor dropped in and had them fill with 10w30 Mobil one. Haven't even had its first oil change yet. Seems to be doing well so far. Before that I ran the same on 163000 mile engine and it was fine til it died. I've heard that once you run synth to not swap back but that's just what I heard. Its up to you really and like everyone else said try to find out what the po used.

 

I've used synthetic before on aging engines to figure out where leaks are coming from. Like the first reply said...oil doesn't cause leaks. Synthetic will just sneak out through a smaller hole. If it's leaking...it was going to be leaking anyway. Might as well fix it.