I have not been able to get a consistent answer to this question from any of the oil reps I have talked to.
For years, I have always believed that GL-5 could not be used in a GL-4 application. I was told by several oil company engineers that the additives in GL-5 are not compatible with the brass and copper bushings in some GL-4-specific applications. So I have always stocked both, for liability reasons.
Now, I am told by a Valvoline oil engineer that their GL-5 is 100% compatible in all GL-4 applications! His explanation was that they now use 'inacctivated sulfer compounds', and that the fluid is now interchangeable.
However, my Mobil oil-guy says that he never heard of 'inactive vs. active', and says that I'm just being hustled.
Mobil says that their GL-5 is good in all applications EXCEPT manual transmissions that call for GL-4 only.
Oddly, they both told me that their GL-5 supersedes the GL-4. When I asked them how, since the GL-classification system is not a superseding system, they both told me that it IS a superseding system!
I have read in several technical sources that the GL-system is definately NOT a superseding system.
Now that I have all this technical support and knowledge, I am 100% confused!
Who's got the answer?
For years, I have always believed that GL-5 could not be used in a GL-4 application. I was told by several oil company engineers that the additives in GL-5 are not compatible with the brass and copper bushings in some GL-4-specific applications. So I have always stocked both, for liability reasons.
Now, I am told by a Valvoline oil engineer that their GL-5 is 100% compatible in all GL-4 applications! His explanation was that they now use 'inacctivated sulfer compounds', and that the fluid is now interchangeable.
However, my Mobil oil-guy says that he never heard of 'inactive vs. active', and says that I'm just being hustled.
Mobil says that their GL-5 is good in all applications EXCEPT manual transmissions that call for GL-4 only.
Oddly, they both told me that their GL-5 supersedes the GL-4. When I asked them how, since the GL-classification system is not a superseding system, they both told me that it IS a superseding system!
I have read in several technical sources that the GL-system is definately NOT a superseding system.
Now that I have all this technical support and knowledge, I am 100% confused!
Who's got the answer?