Diff Oil Change to Synthetic
Thread Starter
JK Enthusiast
Joined: Jun 2008
Posts: 264
Likes: 0
From: Denver, Colorado
The reason I did this in the first place is that I swapped my stock diff covers for Riddlers.
The oil was dark. Not burnt which smells horrible, not contaminated. Just too dark for so few miles. Given how dark it was there had to be a lot of breakdown occuring too. So the synthetic will cure that and I will check it again in 10000 miles or so to see how its holding up.
As for what will go in the transfer case I don't know right off. I have read that the factory uses synthetic there but I have not asked my service writer yet. If I do change it I will probably find the Mobil 1 version of what ever is in there.
The thread tape is probably overkill but no harm is done. I did not use it on the rear diff and it is tight as a drum. No leaking at all after 800 mostly highway miles.
The oil was dark. Not burnt which smells horrible, not contaminated. Just too dark for so few miles. Given how dark it was there had to be a lot of breakdown occuring too. So the synthetic will cure that and I will check it again in 10000 miles or so to see how its holding up.
As for what will go in the transfer case I don't know right off. I have read that the factory uses synthetic there but I have not asked my service writer yet. If I do change it I will probably find the Mobil 1 version of what ever is in there.
The thread tape is probably overkill but no harm is done. I did not use it on the rear diff and it is tight as a drum. No leaking at all after 800 mostly highway miles.
JK Super Freak
Joined: Oct 2007
Posts: 1,446
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From: Statesboro, GA
If I wanted to change mine to synthetic should I clean out the diff or just drain it and add the synthetic? I am thinking about changing the covers which would probably allow me to get more of the existing oil out.
Thread Starter
JK Enthusiast
Joined: Jun 2008
Posts: 264
Likes: 0
From: Denver, Colorado
All modern oils have detergents that keep contaminants in suspension. If you fill with fresh oil there is so little in the way of contaminants left behind that it really won't matter.
Do make sure you clean your drain plug. I was really surprised at how much of what appears to be sludge was on the magnet of the plug. That was true for both front and rear. It may have been what contributed to the darkness of the oil too. Its really just very finely ground metal. So fine that when you rub it between your fingers it just feels like heavy grease. No particles you can really feel.
If you swap out your diff covers later you are going to have the covers off and you can take some brake parts cleaner and give em a good cleaning.
If you know you are going to swap your diff covers out relatively soon just drain and refill with regular oil. The synthetic I put in mine was about $10 a quart.
There is nothing wrong with regular (non synthetic) motor oil as long as you change it from time to time. The big advantage to synthetic is that it never breaks down. You only get rid of it because it gets dirty.
Do make sure you clean your drain plug. I was really surprised at how much of what appears to be sludge was on the magnet of the plug. That was true for both front and rear. It may have been what contributed to the darkness of the oil too. Its really just very finely ground metal. So fine that when you rub it between your fingers it just feels like heavy grease. No particles you can really feel.
If you swap out your diff covers later you are going to have the covers off and you can take some brake parts cleaner and give em a good cleaning.
If you know you are going to swap your diff covers out relatively soon just drain and refill with regular oil. The synthetic I put in mine was about $10 a quart.
There is nothing wrong with regular (non synthetic) motor oil as long as you change it from time to time. The big advantage to synthetic is that it never breaks down. You only get rid of it because it gets dirty.