API GL-5 in GL-4 application

[reb]

Just checked out the thread talking about yellow metal compatibility in some grades of transmission oil. That sparked a question. I gather that GL-5 is made for more demanding applications than GL-4, so it seems reasonable that using -4 in -5 applications is probably not good. Are there adverse consequences in using GL-5 in an application that specifies GL-4?

 

[gsxr1100]

Gl-5 oil has more EP (adds) in the oil and sometime they [transmission] do not like it. Sometimes the synchros do not work.

Now in diff or axle fluid, have at it. USe anything you want.

I would either use a GL-4/Gl-5 oil (dual rated). OR a GL-5/MT-1 type fluid.

Maybe I am wrong here, but this is how I see it.

 

[reb]

Interesting. The reason I ask is the the specs for the SUV I just bought say 80W90 GL-4 is ok for the transmission and transfer case and 80W90 GL-5 is ok for the differentials. I figured it might be simpler to have only one on hand.

Thanks.