Putzing around companies site and found Pennzoil makes a GL-4 80-90! and they also offer a Synthetic 75-90 GL-4. I also found on their FAQ section that GL-4 and GL-5 IS NOT INTERCHANGABLE. I found 2 articles on their site about that. Valvoline's site didn't even touch the GL-4 topic or list a product that had GL-4 as a spec. Pennzoil seems to be ontop of the gear lube for transmission... very impressed with their upfrontness and such. no ohter "main stream" company touches this subject.
Pennzoil GL-4 Gear lube
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Greetings. I'm new to the site. I am a team leader with Pennzoil/Quaker State/Shell at their R&D center in Houston. GL4 by definition has half the treat rate of the extreme pressure additive that is found in a GL-5. The extra chemistry may offer more protection in one regard, but could also promote chemical corrosion of yellow metals in the gear box. I agree that GL-4 and GL-5 are not interchangeable.
Ferndog- I wish Pennzoil's 75-90 GL-4 gear lube was available locally at retailers. Why is only Synchromesh avail?
Where can I get the stuf!!???
I've tried the large local parts houses. Autozone, Advance.... no go. I guess I might try the phone #. I've heard rumors that NAPA carries a CRC GL-4 product for a good price. need to stop by napa and carquest...
GL-4 is for manual transmissions. GL-5 is better for almost all other gearboxes might have to add a Limited Slip additive though.
I went through about 2 weeks of trying to find the synthetic pennzoil gear lube in Illinois, even enlised Johnny from on here and came up with nothing. No one, napa, advance, autozone, oreilly, carquest, nobody.
If you can not get Pennzoil GL-4 the just order either Redline MTL or MT-90 and be done with it. Summit and forget about it. Or see one of the Amsoil Guys. Not that big of a deal.
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