I've done several searches and get a range of answers. What is the best oil to use in a NWC T5 transmission? Answers I have found: 50W gear oil, 75W gear oil, 90W gear oil, ATF.
Yep, that's usually what you hear although somebody might show up to say gear oil is ok in the NWC transmissions. And they probably won't be mistaken, but it may depend on where they live. ATF according to everything I've read will cause slightly more wear on bushings, bearings, etc but we're talking tens of thousands of miles. Gear oil might make it wear a bit less but will make it feel pretty sluggish in cold weather.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
1950 Chevrolet 3100 (Ol' Roy) 1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1956 Cadillac Sixty Special Fleetwood (The Godfather) | 1966 Oldsmobile Toronado (The Purple Knif) | 1966 Ford Mustang (Little Red) | 1964 Ford Galaxie 500 coupe | 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
The WC T5 must use ATF. A Stovebolt member was kind enough to reference his S10 Owner’s Manual and it said ATF for his NWC T5. You will NEVER go wrong with DEX/MERC ATF, no matter what T5 you have, NWC or WC. The ATF called for in the 88-92 Camaro T5 was DEXRON II which is no longer available. Other DEXRON ATF choices are too thin. I’m friends with the owner/operator of a reputable T5 transmission shop in Atlanta and he said to use DEX/MERC ATF. I’ve used synchromesh in a NWC T5 but switched to DEX/MERC. I like it better. I’ve had people tell me their T5 wouldn’t shift properly with gear oil.
The WC T5 must use ATF. A Stovebolt member was kind enough to reference his S10 Owner’s Manual and it said ATF for his NWC T5. You will NEVER go wrong with DEX/MERC ATF, no matter what T5 you have, NWC or WC. The ATF called for in the 88-92 Camaro T5 was DEXRON II which is no longer available. Other DEXRON ATF choices are too thin. I’m friends with the owner/operator of a reputable T5 transmission shop in Atlanta and he said to use DEX/MERC ATF. I’ve used synchromesh in a NWC T5 but switched to DEX/MERC. I like it better. I’ve had people tell me their T5 wouldn’t shift properly with gear oil.
When GM made the leap from dexron III to dexron VI it superceded all prior versions in automatic transmissions. Manual transmissions & shift on the fly transfer cases kept Dex III now relabeled as Manual Transmissions & Transferred Case fluid. I would say that's what the Dex / Mercon is. Dex VI is too slick for the synchronizer to function properly. It is a huge leap forward in older GM automatic transmissions!
Last edited by BC59; 10/16/20245:44 AM. Reason: Add photo
BC 1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc 1949 GMC 250 project in waiting 1960 C60 pasture art Retired GM dealer tech. 1980 - 2022
I concur. Dexron/Mercon is what I use in the Cadillac and Toronado after Dexron II disappeared.
1950 Chevrolet 3100 (Ol' Roy) 1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1956 Cadillac Sixty Special Fleetwood (The Godfather) | 1966 Oldsmobile Toronado (The Purple Knif) | 1966 Ford Mustang (Little Red) | 1964 Ford Galaxie 500 coupe | 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
I had my NWC T5 rebuilt by a local manual transmission shop. The guy recommended 30W oil. I double checked to make sure I understood what he meant when he wrote that on my receipt, confirmed we were on the same page... 30W oil.
Five years later, still good. I haven't been in it to look at wear but it is driving as nice as can be.
When I first got my T5 everyone (including the Chevy site) said to use A/C Delco 10-4014 (Synchromesh friction modified). So that's what I did. It is a NWC. Are people today saying that's not good?
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
