There was some sort of court ruling that some dino based oils are so modified (hydrocracked) they can be called synthetics. Group 3 oils of this type can be labeled "synthetic" in the US, but not in most other countries.

Group 5 synthetics are actually synthetic (man made base stock).

I have run Redline in this and my last truck with good results. (Group 5).

For warranty purposes running anything labeled synthetic that is rated GL-5 in a 75W90 would probably be fine.

 

A true synthetic starts with a man made group 5 base stock. To that is added the rest of the chemicals to give it the properties you're after. A true Synthetic has no dino oil in it.

Most "synthetics" on the market start with a group 3 or 4 base stock, which is dino oil.

A true synthetic has excellent wear properties and high heat resistance. You can run a true synthetic at 250* all day long and not worry about it.

A few years ago, lawyers and marketing agents got together and allowed the use of the word "synthetic" to be applied to any oil that meets certain performance criteria. I think Mobile 1 was the first to use that. According to Mobile 1, they had trouble with their processing plant, and could not get sufficient quantities of the group 5 base stock. That started the cart moving, and all other companies jumped on.

This information (as you would imagine) is very difficult to find. And, I have not been able to find a lab anywhere that will test a sample and tell me what it really is. I have heard that certain M1 oils - like 15W-50, and motorocycle oils - are still made with group 5. But I can't confirm that, so I don't use it.

Now, this is not to say that the semi-synths are bad. They're not. They're better than standard dino oils in all respects. In the right application, they're an excellent choice. For most daily drivers, you don't need a true synthetic, and a good semi-synth will perform just as well for half the money.

But compare Mobile 1 at $8.29 a qt, and Royal Purple at $8.50 a qt, and there's no comparison. The RP is clearly a better product for only a slight increase in price. Since a true synth will last longer in the engine, RP ends up cheaper. And why are we payng premium prices for a mid grade product?

I'v been using Valvoline premium blue in my truck. It's straight dino oil, and fairly inexpensive at $15 a gallon; especially if you get it on sale. I don't drive the truck much, and I don't tow heavy. I change it once a year,and the UOA is still good.

But now It's my daily driver, and I'll be using it more. I'll switch to RP and still only change it once a year. I get mine from Summit Racing, and that saves about $10 an oil change over parts store prices for RP. The cost of an oil change once a year with RP is cheaper than with Valvolin twice a year. But It saves me some work, and I don't have to keep as a close a track of mileage.

If you're on the road a lot, like 50K miles a year, you only need 2-3 changes a year instead of 5-6. If you're paying some one else to do your oil change, that saves a lot of money and time.

I know I talked about motor oils, and this is a gear oil thread. But the concept is the same. M1 gear oil costs the same but won't hold up as well as RP or Redline.

For all the info you ever wanted to know about motor oils, go to www.bobistheoilguy.com

 

Valvoline, 75w90 synthetic gear lube

 

I picked up some Mobile 1 at Advance Auto this morning. Four quarts out the door for $43 and change. Two bottles of the friction modifier from the dealer for $17. IMHO if it's apples and apples, I like saving about $50 over the factory stuff.

What do you guys think about a sticky or something in the WIKI with a list of substitutions for the fluids and filters. Kinda like a quick reference guide.

 

Thanks .boB for the info. I had no idea.

Totallyrad. Are you running friction modifyer in a third gen? If so, why?

 

Last time I changed the rear diff oil, I was able to get the full syn Valvoline 75w90 but this time couldn't find it anywhere near me.. Every store had Mobil 1 75W90 LS... I was really worried about it being a Limited Slip oil, and didn't buy at like 4 stores I went to... then I went home and looked it up, and it's just Limited Slip compatible, but you can still add modifiers if you need to.. So I stocked up on it and just changed the Dodge, and I have to do my LR discovery F/R diffs and TC next.

 

I actually asked Redline if I should run the No Additive version of their oil in the rear end.

The engineer who e-mailed back basically said the LS system in these AAM's doesn't have traditional clutches and doesn't need the LS additive, but that the additive actually makes things slipperier and may reduce temperature... and the additive couldn't hurt anything.

So I run the regular stuff that contains LS additive. No problems at all.

 

For some reason, syns took a huge jump in price the last year or two. Last summer, the parts store were all ~$18/qt for the big name syns. I found RP 85w140 for ~17-18 online, no tax and free delivery. FWIW, It's a little off subject but I had a D80 that ran 280 degrees and that was when I lived in Co. I replaced all the brgs and did a very meticulous setup and it only dropped 5 degrees. I started using 85w140 just before I replaced the brgs and stuck with it because it still ran so hot. NO brand of 75w90 would keep the wear metal off the magnet or give good UOAs past about 12k miles. The 85w140 all but stopped the wear metal and would go 24k and was still fit to run longer. I saw no loss of mpg with the 85w140 even in the winter. I also use RP 85w140 in my AAM cuz it runs on the hot side and I was getting wear metal til I switched. Craig

 

Mobil 1 75w90 synthetic gear lubricant. I change it every 30-40k.

 

Because according to the parts guy at the dealer, the Mopar fluid contains it and the shop guys add 2 bottles when they change the fluid. On reflection, I guess I need to read the Mopar bottle to see what it says. The bottles of friction modifier say they need a concentration of between 2-9% I believe.

 

The friction modifier is for the Dana axles only as far as I know. I hear some have ben using it in the 3rd gens for some reason, but it's not the general plan from Mopar, or the dealers that understand the third gens have AAM axles.

 

I sure can't argue it because I really don't know. I guess the question is will it hurt anything? To me at least, there sure seems to be allot of confusion about it.

 

TO make it even more confusing, check out this link from mobil 1. They only sell gear oil with the LS marking on the bottle..

LINK

 

No, it won't hurt a thing. Don't sweat it.

 

Well, I feel like a dummy. It would appear the problem is deeper in the rear. Replace the bearings, install one axle, spin the hub and the roar is still there. Guess this is really going to suck!