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Posted by Kaleb (Black '93 GXE 5spd) on June 08, 2002 at 18:33:08:
From reading around the Net, it seems that the difference between GL-4 and GL-5 is that GL-5 has a higher Extreme Pressure rating (good), which means its additives allow it to function effectively at higher temperatures and pressures than GL-4. So, basically, you can use a GL-4 in a GL-4 application. Is this correct? When I went to Autozone today all the Exxon, Valvoline, and Mobil gear oils were GL-5. Redline has both GL-4 and GL-5 oils. Royal Purple's 75W90 is GL-4 and GL-5 rated according to the label. Anyone else know more than this about the subject? -=Kaleb=-
Our service/owners manuals say to use API GL-4 lubricant in our transmissions.