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Hi everyone,
Needed to purchase tranny fluid for turbo 350 in my 78. Back injury has kept me out of driving her for a long time.. Quite a bit has weeped out, none on the dip stick. What do you recommend? In the past I have used Penzoil ATF Dextron lll for older vehicles. Cannot locate in any of the auto part stores near me. They recommended Dextron VI. I didn't purchase any because I had to many questions they couldn't answer straightforward enough.
What's your thought's on this?
Thanks,
Kenny 78
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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Dex VI is full synthetic. It will work just fine in your 350, tho you might notice a leak(or more) after running it in there for a while. The syntetics have smaller molecules, and the fluid will find ANY small opening that will allow a leak. Not sure why you cannot find any Dex III...it's still available. You can also use a Type F(Ford) fluid with no problems, assuming there are NO issues with the trans now. Type F fluid can sometimes firm the shifts up somewhat, due to the friction enhancing formula. Matter of fact, the fluid B&M sells is actually Type F fluid, in B&M containers.
Edited 7/24/2026 7:08:19 AM (AZT)
Joel Adams
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Send PMLoir en Vallee SARTHE, France
Joined: 8/21/2002
Posts: 186
Vette(s): 1978 L48 Auto. Red with Oyster Leather interior. Owned since 1990.
I've always stayed with a Dexron III ATF fluid, usually Castrol over here. Any of the Dex III variants are backwards compatible.
Personally, I wouldn't use a Synth fluid. I had a long discussion with a man from Mobil 1 a few years ago now at Sebring and he was very frank about the qualities of synth oils and fluids. Though he said they were super, he was well aware that used in older engines or transmissions there was a very good chance of leaks.
I have a persistent weep from the speedo drive of the trans on our '78 which manifests itself if the car stands for more than about a week to ten days. In reality, it loses about 1/3 pint in a year max, so it's not the end of the world. But a change of the gear and housing has so far failed to stop it, so the last thing I need is a fluid that will increase the chances of leaks!😀
I found Castrol Dex III fluid on Amazon: https://www.amazon.com/Castrol-03520C-TRANSMAX-MERC-Gallon/dp/B00DILUBL6/ref=sims_dp_d_dex_ai_rank_model_1_d_v1_d_sccl_1_1/141-5759881-7102310?pd_rd_w=DnjsU&content-id=amzn1.sym.bb4a0aac-c2b4-4b4b-a0c8-9aa89b28dce3&pf_rd_p=bb4a0aac-c2b4-4b4b-a0c8-9aa89b28dce3&pf_rd_r=J7G3EZ5ZF59STTVSKH38&pd_rd_wg=cm0eI&pd_rd_r=6f68427a-4def-4e76-b896-2c279f8ef343&pd_rd_i=B00DILUBL6&psc=1
Stephen J Irons
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