Mixing gear oils

[digitalSniperX1]

I'd like to do this (let's just say it's convenient) but I'm not sure it's a good idea. I have about 3/4 quart of Amsoil SVT (75W-110) and would like to mix that with Supertech Semi Synthetic (75W-90) 3 1/4 quart in a Mazda3 manual transmission calling for GL5 75W-90.

Any reason I shouldn't do this?

 

[lewdwig]

I see nothing injurious in doing this, may affect your shifting.

 

[digitalSniperX1]

Well, the stuff in there is at 45,000 miles, and it shifts just fine. So if I feel no difference with the new stuff, I'm ok with that.

It's supposed to be changed more often than I've done but I've been a bit negligent (80% highway miles on this car though).

 

[PT1]

I use up all my "orphan" partial bottles all the time like that and have never had an issue. I just don't go extended OCI with them.

 

[webfors]

While my manual states not to mix, I think that's a little too general. If they are both rated the same (GL-4 or GL-5, etc) you should be fine, especially if both gear oils state they are 100% compatible with other similarly rated gear oils, which I believe the two listed above are.

 

[mechtech2]

That Supertech is not really a gear oil designed for manual trans shifting sweetness.

 

[SilverC6]

It sounds like the factory fill is working fine.

Why not just use the 75W-90 that is spec'ed?

I'd order up the required amount of Amsoil in the correct weight and change it out.

 

[digitalSniperX1]

Thanks for the input. I've changed my mind and will do exactly what you said (Amsoil all the way on this one).