Mixing Gear Oils

[digitalSniperX1]

I've heard that some mix GL-4 and GL-5 gear oils for shift feel. Are they chemically compatible or are there any issues I should know about?

I have a 2 quarts of Amsoil MTG and 2 quarts of Amsoil SVG which I may put in a Mazda 3 transmission (the owners manual says either gear oil spec is ok).

 

[Mr_Joe]

It may not be the best habit but if the two types are O.K. for the vehicle I wouldn't have a problem mixing. This would especially be true for me with gear oils. I do it with motor oil at times too.

 

[Eddie]

Generally not a good idea to mix gear oils because of different additives may cause problems.

 

[digitalSniperX1]

I suppose if one doesn't know for sure then error on the side of caution which will cost me 10 dollars. Probabaly the wise choice.

 

[mechtech2]

Not many GL5s are made for good shifting in manual transmissions.
There lies the real crux of the problem.

 

[gamefoo21]

GL4 for a transmission with Syncros, GL5 everywhere else. MT-90 is pretty close to being GL5 but it can't deal with Hypoid gears.

If in need of a stouter manual transmission oil, Redline's Lightweight Shockproof does GL5 while maintaining the proper friction numbers for good shifting. There is also Motul 300, it's a another very good oil.