What oil for 4 speed transmission?

[diesellibrarian]

So maybe it urban myth, but I was under the impression you were never supposed to mix viscosities. The advice I got this from was motor oil, but I assumed it would apply to all oils. Is it wrong?

No idea. I’ve happily mixed oils for many years in many different cars and have never had a problem. But that doesn’t mean it’s a good idea haha.

 

[Slow1]

It's not so much the oil and more the compatibility of the additive packages. The additive packages control the multi-weight properties of the oil, and to a lesser extent extreme pressure additives that protect when the oil does shear, i.e boron, zinc, sulfur, etc, and foaming control, and detergent. That being said I don't think there are too many people that have had an issue or know anybody that has had an issue. As for mixing viscosities. Think of a container of oil like a room full of balls. The balls represent the polymer chains which dictate viscosity. Conventional oil would look like a room full of all size balls, basketballs, tennis balls, golf balls, bowling balls, ect. Synthetics have more evenly length polymer chains, i.e. a room full of only tennis balls.