Accidentally put in half a quart of MT-90 into rear diff. Is it ok?

Hello,

I just got a 2000 Tacoma and was going about changing all the usual fluids (engine, diffs, trans, crank case).

Was already tired when I was filling the rear diff, and accidentally put in about half a quart of Redline MT-90 oil before I noticed! I filled the remainder with Redline 75w90 but am now worried if it's going to be ok? or if it's safer to dump everything out of the rear diff again and refill with 75w90 only? It's an expensive mistake but I'd rather not mess anything up in the future. I plan to have this truck reliably running for the long haul.

I've read that MT-90 can be detrimental in the differentials and should only be put in the transmission, but have found no concrete answers.

 

Dump and refill

 

What's the damage? Can I drive on it for at least 100 miles?

 

Yes

 

I wouldn't drive it. Screw that. Would you rather buy $20 bucks in liquid or $100s of bucks in new diff and labor to replace?

 

I'd drain and refill asap. When the diff gets hot, crazy shit could happen. $$$$$

 

It's not the end of the world, but I wouldn't leave it in there any longer than you had to. A GL-4 oil does not have the additives that provide the protection that diff gears need. Since you mostly filled with a GL-5 oil, you are probably OK to drive to the store to get more. I'd worry if there is any strange reaction between the two types of oils. Anyway, don't be too worried about it, just get it changed soon.

 

MT 90 is a 75w90 gear oil. You aren't going to blow anything up for a few days.

However, it is GL4, and your diff wants a GL5. The GL4 is for the trans, and is protective of brass syncros.

While you can spend the $ as you see fit on product, I'd suggest you just get some OTC

$30 Mobil 1 75w90 Mobil 1 104361 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

Mobil 1 75w90 GL5 and do your change. Cheaper, easy to find, quality product.

The next time you do a trans fluid change give

$34 Ford XT-M5-QS Full Synthetic Manual Transmission Fluid - 1 Quart , black

Ford XT-M5-QS a try. I've seen it make shifters that were notchy even with Redline work like butta. Be careful at the Ford dealer. Some of the parts guys might try to slip you something else. Unless you have some SVO jocks in your area, it's likely they'll have to order in the fluid for you.

 

The potential problem of running MT-90 in your differential is not its weight, but its rating (GL-4). It is not designed for the pressures of a differential.

Personally, I would change it and not take the risk of causing any damage. If you do have to drive it, post again after you change it and let us know if there was any metal on the magnet...that could be useful information for someone down the road in the same situation.

 

Ouch. I've driven about 50 miles on it already, will try to get it changed ASAP and not drive more than I have to.
Will report back on the metal shavings..

 

Go do it right now man.

 

Mikey don't worry. you have a GL4 75w90 gear oil in your diff that almost meets the specs of what youre supposed to have. you can go a few thousand miles so long as youre not putting serious load on your truck.

but you should change the oil for a GL5 the very moment you have a chance to, and no later. Also, you'll need new washers, don't forget that.

 

Don't hammer it and you won't find a thing.

 

Though really, if it was just light driving, youll be fine. Just drain and refill.

 

+1 to all of this ^^.

I doubt POTENTIAL damage would be immediate or severe, but Toyota specs specifically call for GL-5 gear lube in the differentials. As noted by others, the primary difference between GL-4 and GL-5 is the amount of extreme pressure additive package. GL-4 has less than GL-5 provides, so you're less protected against harsh use. Go easy on it and change it out as soon as you can.

 

Yes, that's right! GL-5 became full Hypoid-Gear (spiral beval vs standard gear) oil, that's really the only difference. It handles higher pressures from the spiral beval. Just don't push your truck.

 

Y'all need to chill, it'll be fine.

 

It does appear to be fine.
Got it changed today with no apparent adverse effects.

The magnet on the drain plug did not have anything on it. This is after about 60 miles of driving with half a quart of MT-90 mixed in.. it has been an expensive oil change!

 

That's good to know, thanks for posting.

 

agreed, you guys are really over reacting.