using 80w90 in place of atf?
 

one of my friends just got a hold of a 89 f150 4x4 with a mazda 5 speed that is BEAT all to hell. i helped him to get it running and we were changing fluids and filters on it and when we drained the manual transmission there was a needle bearing stuck to the magnet on the drain plug!!!

im 99% sure that was the factory fill atf that we drained out of the transmission and transfer case. he replaced the fluid with valvoline 80w90 gear oil. i told him we had better put atf back in there but he insisted that gear oil would protect it better cause its so worn.

did he do the right thing? or should he had listened to me and put atf in the trans and transfer case

i drove it a couple of times and it does seem to shift smooth, for having over 290k miles on the orignal trans and 300/6

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Well, it will prob be ok if its not in cold weather.

When I got my ZF 5speed the farmer had put 80w90 in it, I drained it n put atf in it, it make horrible noises. So drained it againn and put 5050 mix of atf and Lucis oil additive. Quieted it right up, BUT it didn't shift easy at all in cold weather. Had to put the tcase in "N" n trans in gear and let it run like that for 10-15 min.

So, I drained it again, and this time put Royal Purple ATF in it(expensive but well worth it IMO) and it is now quiet, and shifts nice! :D

yeah that royal purple is some expensive stuff!! i used to buy it all the time before it got to over 8 dollars a quart.

i have driven that truck with temperatures in the 20's with no warm up time at all and it shifted ok. it wasnt "tough" to get into gear by any means but i wouldnt say it shifted like "butter" either. it did get easier as the truck warmed up now that i think about it.

i was just concerned that the gear lube was way too thick and the transmission and transfer case would die from lack of lubrication


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once it gets cold, you will break the trans. it is designed to use ATF, not 90 weight sludge.

My brother-in-law just replaced his F150 trans (M5OD) and the shop he got it from said to use 10W-30 motor oil or they would void his warrantee.

Jfyi, ATF is about same viscosity as strait 10w oil.