Hey everyone, been lurking for a while now and decided I'm on this site enough might as well make it official.
So for my first post on here I would like to know if I'm OK running Royal Purple 75w90 in my differential. I just changed it out a week ago and I'm getting a faint whine while driving, nothing annoying or too loud. I don't know the history of the car, so not sure if this has ever been serviced, of course the old fluid stunk and was just nasty to look at. Overall despite the very faint whine the car is running like a new car. Tag on the diff calls for 80w90 FYI.
Basically just wanting to know if I should put the 80w90 in or stay with the Royal Purple, only if the whine could be an issue or if its normal I'll just stick with it since it is running so well. Just don't want to make an issue where there normally wouldn't be one.
Thanks for reading and sorry for being long winded!
Vehicle in ? is in my SIG...
01 300m differential oil
- Thread starter kwooten31
- Start date
- Status
We had a couple of 96 Intrepids with the 3.5...I'm sure the diff was the same as yours. The service manual said not to use synthetic fluid in the diff, but didn't say why. I used a parasynthetic (syn blend) in the diff (both cars) and never had an issue.
Thank you for the reply, I think maybe I'll just drain and fill with conventional oil to avoid any issues. Thanks again!
Before you waste all that money you spent on the RP, why not try putting in 4oz of friction modifier for $8-9. RP says it has the friction modifier additives in it, but it caused my diff to whine above 40mph until I added the FM.
I don't see a reason why you "can't" use synthetic. Going down to a 75 from 80 shouldn't cause the issue either.
Originally Posted By: lugNutz
I don't see a reason why you "can't" use synthetic. Going down to a 75 from 80 shouldn't cause the issue either.
Originally Posted By: lugNutz
Before you waste all that money you spent on the RP, why not try putting in 4oz of friction modifier for $8-9. RP says it has the friction modifier additives in it, but it caused my diff to whine above 40mph until I added the FM.
That's my thought now for sure! I know my LS diff in my Explorer needs an additive. I did a bunch of research on the different 75-140's and some had the FM in it, some didn't. Read some M1 problems with their additives not being enough, so I went with the RP. Unfortunately theirs didn't have enough either!? I had to crawl back under and add the FM anyway, but the whine went away after. I will be changing it out again in the not too distant future with ST syn 75-140 with Motorcraft FM.
That's why I suggested to the OP to try an $8 bottle of FM before he throws away what I am sure is over $40 in RP. Plus, it won't hurt to just try!
MolaKule
Staff member
For a replacement fluid that specs 75W90, I always go with a 75W110.
Amsoil SVG, Redline, and Lubrication Engineers all have a 75W110.
Why? Good cold weather and high temp viscosimetrics, thicker overall fluid film between gears, and super EP PI packages.Originally Posted By: MolaKule
For a replacement fluid that specs 75W90, I always go with a 75W110.
Amsoil SVG, Redline, and Lubrication Engineers all have a 75W110.
Why? Good cold weather and high temp viscosimetrics, thicker overall fluid film between gears, and super EP PI packages.
MolaKule
Staff member
Originally Posted By: 4wheeldog
Originally Posted By: MolaKule
For a replacement fluid that specs 75W90, I always go with a 75W110.
Amsoil SVG, Redline, and Lubrication Engineers all have a 75W110.
Why? Good cold weather and high temp viscosimetrics, thicker overall fluid film between gears, and super EP PI packages.
Last edited:
MolaKule
Staff member
Foaming should not be an issue with modern differential lubes.
As for the Chrysler non-synthetic spec, was this from a Haynes or similar service manual or from the Chrysler service manual?
Seal swell (ASTM) testing specs are the same for mineral or synthetic fluids.
Originally Posted By: MolaKule
Originally Posted By: 4wheeldog
Originally Posted By: MolaKule
For a replacement fluid that specs 75W90, I always go with a 75W110.
Amsoil SVG, Redline, and Lubrication Engineers all have a 75W110.
Why? Good cold weather and high temp viscosimetrics, thicker overall fluid film between gears, and super EP PI packages. 
I dealt with the conventional vs synth question on my 2000 Concorde. The factory line is clear, no synth. They have a factory lube for this application that has some kind of a claim of fuel saving. Never priced it and went with Valvo conventional 75W90.
The original spec for this diff is 1 quart. Seems there is a recall due to spewing when hot. It includes a redesigned vent and a new fill of I think 16 OZ. I've not lost any fluid with a full quart fill since I changed it 45K ago.
I never got an explanation for the no synth requirement, but followed it. I suspect the best lube for this application if sticking with a conventional is Chrysler's own, but I figured Valvo was good enough for 1/4 the cost.
As far as the OPs whine, I'd try some name brand conventional, and the OEM lube if you want to spend the money. I'd install a quart unless you ever get some spewing.
Chrysler may be using bearings in the diff that have polyamide 6.6 cages. These polyamide bearing cages do not like synthetic lube, especially synthetic lubes with Phosphate esters. This has caused gearbox failures in the Moto Guzzi community by lowering the allowable operating temperature of the bearing.
MolaKule
Staff member
Originally Posted By: OMCWankel
Chrysler may be using bearings in the diff that have polyamide 6.6 cages. These polyamide bearing cages do not like synthetic lube, especially synthetic lubes with Phosphate esters. This has caused gearbox failures in the Moto Guzzi community by lowering the allowable operating temperature of the bearing.
Last edited:
Redline makes the best gear oils I've ever used. From 4x4 diffs to racing at the track redline gear oils actually make me break my rule about expensive lubricants. I've found that they are worth the extra few bucks.
Here's the service bulletin:
A running change was made to reduce the fluid level in the differential from 946 ml (32 ounces) to 739 ml (25 ounces). This change is to reduce the potential for a fluid burping condition as described in Technical Service Bulletin 21-10-99. In some severe conditions, Technical Service Bulletin 21-10-99 is still applicable.
Differentials filled to this lower level can be identified by the fluid level being approximately 9 mm (3/8 inch) below the fill opening.
In addition, the reduced level will require a change to the maintenance schedule. This interval is described by Schedule B (severe service) maintenance in the service manual or owners manual. The Schedule B interval for differential fluid is every 24,000 km (15,000 miles).
If any service is performed that requires differential level fill procedures, be sure to fill it with only 739 ml (25 ounces) of MOPAR 75W-90 Gear Lubricant p/n 05010320AA.
The last time I saw such a car, it said 75w90 non-synthetic on the differential.
The only oil I could think of that matched was Valvoline.
Practically nobody seems to know about the final drives with longitudinal FWD, but they seem to hold together despite never being given an oil change at all.
- Status
Similar threads
