I’ve never changed the differential fluid in my 2015 Forester (85k) and figured it’s about time. I went to pick up three quarts of Diff fluid at the local auto parts store. They had a great sale on Valvoline 75w-90, but only had two of them. They had Mobil 1 75w-90 for a few dollars more. I bought the two Valvolines and one Mobil 1. The diffs call for about 2 quarts total, though I’ve seen write ups that say as high as 2.2 quarts. I figured I could put the Valvoline in and top off with the Mobil 1 if necessary. That should be fine, right? We’re talking maybe 1/10 to 1/5 of a quart of Mobil 1. They’re both full synthetic, same weight. I should be able to sleep at night for the next 30-50k, yeah?
Mixing Differential Fluid
- Thread starter Chuck61
- Start date
It's fine but not ideal. If a tech at a dealership checks a diffeential oil level, say for PDI, he will add the fluid the dealership provides, and that is not likely the exact same as the original fill.
It's not ideal, but it's not disaster either.
It's not ideal, but it's not disaster either.
I believe I've read on this forum that the API GL-5 specification requires that this lube be miscible with other GL-5's. To me that means its fine to mix them. Can anybody else corroborate?
PDI the differential??????????????????????? Not on ANY of my cars. All were low. Complained. Answer. "It's new, it can't be low."
Most Subaru rear diffs use just under a quart. The front uses somewhat over a quart (like 1.3 ish) If I were in your shoes, I'd use the M1 in the rear, and the valvoline up front. You'd still have enough of each left for top off from and rear respectively.
That makes sense. I’ll do that. For some reason I had it in my head that they had to be the same, but of course they don’t.
Any dealer that includes the differential (with no obvious signs of leaking) in their PDI would be a very rare one indeed!
People have been adding whatever brand they had since forever.
Depends on the car, my XJ? yea I mixed a left over half a quart from the Camaro with some Bulk Valvoline.
Camaro? Nah its getting 100% the same fluid.
Camaro? Nah its getting 100% the same fluid.
There's a guy with a truck with 350k miles on it and no major issues. He's always thrown whatever gear lube on hand into his diffs when he changed it, including Supertech, Valvoline, and other house brands.
After reading this, I'm going to give him a call and tell him it's not ideal.
After reading this, I'm going to give him a call and tell him it's not ideal.
I do it.
I would not bother with the single odd quart of Mobil 1, just use the 2 quarts of Valvoline. Even if the capacity is 2.2 quarts, putting in 2 fresh quarts is a good service, just top it off with a little of the old oil. I do this all the time in my manual transmissions and differentials, never had a problem and they run forever. The machine is not going to explode if 10% of the oil is not perfectly fresh.
Otherwise you'll end up with an open, mostly full bottle of M1 gear oil that is going to sit around forever. Just take it back.
Otherwise you'll end up with an open, mostly full bottle of M1 gear oil that is going to sit around forever. Just take it back.