I'm going to have to disagree with your buddy. While the motor oil might not hurt anything, I don't see any reason to use it instead of the proper grade of trans fluid. I grew up around a shop my father owned in Nashville, and he was the second man in middle Tennessee to work on automatic transmissions, beginning in 1945 or so. From the mid-40's to the mid-60's, he probably worked on thousands of transmissions of all types. The original automatac trans fluid was "Type A, Suffix A", which contained a little sperm whale oil. Since whaling was banned, or at least severely restricted, synthetic oil similar to whale oil was added to transmission fluid, resulting in a bunch of special designations.
There are about 4 or 5 varieties of the "Dexron" fluids, depending on the year and performance level of various transmissions. I think Chrysler runs a dedicated fluid, as well as some of the import cars. All of them run a bunch of friction enhancers and other additives that just aren't present in any motor oil. Trans fluid must help the clutches lock up firmly, yet engage smoothly, and it must lubricate moving parts at the same time. It must also transmit pressure efficiently. There are detergents and anti-foaming agents different from, or not present in motor oils. Transmission fluid has to do a lot more than motor oil, so I don't see any advantage to mixing a foreign fluid into the situation. Ditto for transmission "additives" unless you're trying to solve a specific problem like slippy clutches or pressure leaks past hardened clutch piston seals.
Jerry
Last edited by Hotrod Lincoln; 09/26/2008 5:25 PM.
