Mixing MTL to achieve viscosity

[bigcart]

Recently picked up a 91 F150 with the inline 300 and M50D and would like to change the transmission fluid. Original spec called for Mercon. Motorcraft Mercon V and Valvoline DexMerc are the closest things I could reference for viscosity, resulting in 33.2cst @40 / 7.5cst @100 and 34.5cst @40 / 7.1cst @100 respectively.

My plan is to mix 3 quarts Redline MTL-LV and 1 quart Redline MTL in a gallon. Viscosity calculator says this will produce a 34.01cst @40 and 7.03cst @100 fluid.

My questions are: how well do you think this will work? And if so, what would be the benefits over using Redline D4, (35.4cst @40 / 7.5cst @100)

Am I off base for thinking a dedicated manual transmission oil product (MTL) with proper viscosities will perform better than an ATF that is designed to also work well in manual gearboxes (D4)?

And yes I did search, but the mixing others have done in the past involved mixing MTL and D4. I feel that using MTL-LV in the place of D4 for the mixing would be better practice.

 

[MolaKule]

Redline MTL which one?

 

[Pablo]

I've mixed MTF fluids, but not ATF and MTF.

I would just use a 7.5cSt ATF like this: https://www.amsoil.com/p/amsoil-oe-...c-automatic-transmission-fluid-otf/?zo=515729

or

https://www.amsoil.com/p/amsoil-sig...c-automatic-transmission-fluid-atf/?zo=515729

A 1991 MT won't know the difference between 7 and 7.5

You could probably use a 9-10 cSt MTF

 

[bigcart]

Redline MTL which one?

Redline MTL in my post was referring to the original 75w80 GL-4.

 

[MolaKule]

And yes I did search, but the mixing others have done in the past involved mixing MTL and D4. I feel that using MTL-LV in the place of D4 for the mixing would be better practice.

The MTL's you are mixing have higher levels of anti-wear chemistry than any ATF, so that is a plus.

 

[bigcart]

The MTL's you are mixing have higher levels of anti-wear chemistry than any ATF, so that is a plus.

Thank you for the reply. This is what I am thinking as well. While I know that this particular trans won’t be too picky, it’s good to know this would be a good protocol for other trans calling for ATF. If you wanted to you could dial in the viscosity by mixing different MTL offerings by the ounce if you were dealing with something finicky. As well as ending up with an overall better fluid in the transmission.

 

[Marcozi]

Contact Redline. They will tell what to mix.