Vintage Mustang Forums banner

1 - 4 of 4 Posts

·
Registered
Joined
·
467 Posts
Discussion Starter #1
Hi!
I buy Valvoline Gear Oil 80W-90 and I have 1 qt of Valvoline Gear Oil 85W-140. Can be mixed inside my Top Loader 4 speed? I friend told me that is good for the trans. Or should I buy just one kind of viscosity? What is the best for the trans?
Thanks!
Fer ::
 

·
Registered
Joined
·
215 Posts
The best idea is to keep the viscosity consistent. I don't mix oil, myself, and was always taught not to. I am not sure the exact reasons, anymore, but they taught us in shop not to...
What do the others have to say???
 

·
Registered
Joined
·
2,374 Posts
I was curious as to the answer to this one, as I have done it before as well (mixing Crank Case oil anyway). I always thought that since the viscosity of the oil changed anyway as the oil was used, that it wouldn' matter becuase if you are a quart low and add a new quart, you really are mixing viscosity.

While this seems to be true, it isn't the mixing of viscosity that could cause you problems, it seems from this link that the the problem would be becuase you are mixing the polymers that are used to change the range of viscosity.

Here is the web page:

http://www.repairfaq.org/filipg/AUTO/F_oil_facts.html

This seems to be the statement that I think tells you you shouldn't use additives or mix oil types:

Oil additives should not be used. The oil companies have gone to great lengths to develop an additive package that meets the vehicle's requirements. Some of these additives are synergistic, that is the effect of two additives together is greater than the effect of each acting separately. If you add anything to the oil you may upset this balance and prevent the oil from performing to specification.
I'd still like to hear from others as to what their opinion is and if this conclusion is correct...
 

·
Registered
Joined
·
3,595 Posts
It doesn't bother me to mix 10W-40 with 10W-30, or 5W-30. The gear oils you mentioned (80W-90 and 85W-140) might have significantly different polymers in them, even though made by the same company. It will probably only make the resultant mix a bit more viscous, but I don't think I would do it.
 
1 - 4 of 4 Posts
Top