dino or synthetic for diffs?

[Doug Hillary]

Hi,
Mike_dup1 - You said:

"People tend to think because its synthetic, its all the same."

Correct, and in researching this issue one of the largest Manufacturers of complex and expensive drive lines said;

"A poor additive package in synthetic oil offers no advantage over a thermally stable additive package in a petroleum mineral base stock"

So true!

 

[wn1998]

I have amsoil gear lube in my jeep and just plan to change it every 50k. You shouldn't need to worry about it unless you are going off road and get water in your diffs.

 

[meep]

Originally Posted By: J. A. Rizzo
Originally Posted By: meep
every dino diff that I have put synthetic in has rewarded me with a slight (0.5) mpg increase. Period.

97 legacy (front & rear)
97 pathfinder (rear -front had manual disconnects)
2008 cherokee (rear, 2wd)


How did you equalize all the other factors and isolate just the differential fluid as the source of the increase?


Great question. In the legacy, I drove same commute, 450 miles per week. It was very easy to see the before/after over several thousands of miles average. Same with the pathfinder. The diff fluids were changed alone, with no other changes at the same time.

The Jeep, I did swap 6qts of ATF at the same time, so the results could be skewed there.

Here's what I recall: on average, the subie went up 1 mpg overall.

on the p-finder, it went up .5 mpg after rear diff done. syn ATF gained another .5 mpg. manual disconnects were worth a full 1 mpg. all done apart from each other.

on the jeep, diff + ATF, I'm seeing roughly 1.5mpg, but it's harder to gauge-- my commute varies and this vehicle is much more sensitive to seasonal temps, and i don't do the mileage that i used to so i don't have as much real data. I could honestly call it 2 mpg and feel ok about it, but I'd rather stay conservative.

OTOH, I've never had syn engine oil make any difference, though I'd want to believe it did...

M

 

[Zaedock]

If you frequently go off road or have a modified vehicle with the chance of having to repair trail damage, regular gear oil is perfectly fine.

 

[Maritime Storm]

Years ago the founder of this, Brother Bob, actually tested this. One thing he noted in the test was that synthetics had a tendency to not climb gears at low speeds. My thoughts on this subject, follow the manufacturers recommendation for fluid, and change it more often then they ask you to.

 

[Y_K]

Conventional oils are not all the same too. AFAIR, not every syn gear oil has as many extended warranty certs up to 500k miles as Chevron Delo ESI line: Mack GO-J PLUS, Eaton, Dana Spicer, ArvinMeritor.

On the syn side, I like the fact that continuous use of syn oils leads to demonstrably lower seal and gasket failures. Among other benefits and advantages of syn.

 

[AzFireGuy79]

"On the syn side, I like the fact that continuous use of syn oils leads to demonstrably lower seal and gasket failures. Among other benefits and advantages of syn".

Precisely why I use synthetic gear oils. Redline, Amsoil and Mobil 1 are some of my favs. Two of which use Lubrizol for their additive packs. And Roy Howell (use to work for LUBRIZOL) is one of the additive gurus!

 

[JeepRubicon2k3]

Try to find a gear oil that meets SAE J2360 standards and be done with it. I run M1 75w140 in my Jeep Dana 44s.

 

[PDX2500HD]

Royal purple 75/140 with Mag Hi-Tec cover to allow 7.5Quarts in my rear diff...

 

[Audi Junkie]

Save the synthetic for the transmissions, but Mobil 1 is cheap and good. I can't imagine going thru the effort of changing it and cheaping out a few dollars.

 

[Kestas]

I'm not a real synthetic user, but it only makes good sense to use synthetic in differentials. Auto manufacturers are beginning to use it for factory fill. This is to boost their CAFE numbers. The better gas mileage afforded by synthetic far outweighs the price for premium fluid for only a 1-2 qt fill that lasts 60-100K. This same argument is harder to make with other applications such as motor oil or transmission fluid where many more quarts are needed, plus shorter change intervals.

 

[Rickey]

Originally Posted By: wtd
I know that putting synthetic Mobil 1 diff fluid in the rear diff of my 98 K1500 at 20,000 miles, didn't keep my pinion and carrier bearings from starting to fail at about 75,000 miles. This was on a truck that never towed anything bigger than a 5x10 utility trailer and never hauled anything heavy at all.

I run a conventional diff fluid now.

Wayne


I had a similar experience with my '96 Caprice.
At around 70 thousand miles out with the factory fill and in with Mobil 1 75W90.
There was only a tiny amount of fine metal shaving "frost" on the magnet at this point.
At a few thousand miles after the Mobil 1 fill whining noises started.
This turned out to be a failed front pinion bearing.(badly chewed up)

Admittedly this could have been a coincidence.

However I am wary of repeating this unhappy experience.

Rickey.

 

[meep]

i'd like to say coincidence, but who knows. syns in diffs of mine over the years:

97 legacy: F/R and 5spd: dyson syngear II
97 pathfinder: Mobil 1 in rear (dino in front but manual disconnect so it never spun)
97 miata: mobil 1 in MT and diff
93 jeep: valvoline syn 90 weight F/R
08 jeep: xw-140 read (2wd)

knock on mdf....

M

 

[EricF]

I hate to admit this..but my 93 Ranger 4x4 has 227,000 and I've only changed the diff fluid one time using valvoline 80w90 conventional oil and the motorcraft limited slip additive.
I'm long overdue for a change.. just havne't had the time and I hate to admit to that too..
But my plastic diff cover is holding up really well!!
And my front diff.. probably has maybe 100miles total on it.
But I'll have to change that too. it's easier.. suction gun to get that out.

 

[Bror Jace]

I could run anything in the diff of my 2005 Honda S2000. Instead of some $$$ synthetic, I decided to try Chevron DELO 80W-90 ESI conventional oil ... for the borate-based additive package. This 2,800 lb. car has a tiny diff that works quite hard and is very tough on oils. The factory oil (75W-90?) was completely shot at 15,000 miles and the rear-end emitted a rough, mechanical noise at all speeds. Changed the oil and it became quiet enough for me to hear the light noise of the disc brake pads rub on the rotors.

Whatever you do, change it frequently ... about twice as frequently as the dealer recommends.

Yes, a lot of diffs are neglected and seem to survive. But how many of us have ridden in a neglected high mileage vehicle and have heard that distinctive rear end howl?

Thanks, I'll change the gear oil in my rides every couple years or so.

 

[dailydriver]

I would try the ESI, but it seems harder to come by than the rarest and most exotic of boutique gear oils (around here at least).

I have NEVER seen it on a shelf anywhere, and the NAPAs and other local stores cannot even order it in for me.

 

[unDummy]

If I had an s2000, I'd use a 75w140, or install a pumped cooling circuit.

I would always use a synthetic on a fluid that is usually neglected and often forgotten.

If you claim a failure on synthetic, I'd wager that the failure was a faulty component or low oil level. Remember to check the gear oil levels cold every year or every 2-4 oil change intervals.

 

[INDYMAC]

I think you could be spot on here unDummy. I'm using SAE 110 now, but might step it up next summer.

Originally Posted By: unDummy
If I had an s2000, I'd use a 75w140, or install a pumped cooling circuit.

 

[Bror Jace]

"I would always use a synthetic on a fluid that is usually neglected and often forgotten."

But my S2000's rear-end will not be neglected or forgotten. Next change will be in just a couple thousand miles to (hopefully) flush out the last of the gunk created or left behind by the ruinated factory oil.

"If I had an S2000, I'd use a 75w140, or install a pumped cooling circuit."

I wouldn't rule it out ... but the 80W-90 stuff is going to have to let me down before I move on something thicker ... either Amsoil 75W-110 MTG or maybe even the thicker Chevron 85W-140.

dailydriver, I looked around for the better part of a decade and finally found a Chevron dealer just over the state line in Western Mass. He's local to my area and will deliver for free to my place of work ... even sent me a Christmas card this year.

I bought a whole case from him ... and sold 3/4 of it to a fellow BITOGian who, like you, was having a hard time finding this stuff.

 

[pidster]

Changing diff oil can be incredibly easy, like my old Tercel where the diff is contained within the transmission housing and shares the same lubricant supply. Drain plug, fill plug. Done. On my Ranger, you have to remove the diff cover to drain it, then new gasket and refill. In ways this is better as you can clean out any metal shavings etc from the diff completely. In ways it's not because it's a bit of a job, and just to change fluids. I9'd like to change out both diffs, trans and transfer case early for any break-in wear (only 20k on the truck so far) and whenever I tackle that synthetic is definitely what I want to put in all of them. These places are where I'd like a longer drain interval and where the cold temp visc. will have the largest impact on MPG.