fieldsleah

I recently bought a 93 Ranger 2.3L and a 5 speed manual Mazda transmission with 187k miles. Went to check the level of oil in the transmission looks like it has sae 90 gear oil. The service manual calls for Mercon automatic transmission fluid. What kind of problems can I expect, if I drain the gear oil out and re-service with Mercon transmission fluid? I don't want to make things worse since the truck is running fine.

Thanks in advance

360ci

Never use ATF in a manual transmission!
Gear oil is all you need to run. In some cases, engine oil can be used if gear oil cannot be found. Mercon might have their own manual trans gear oil to use, but it's not necessary. Anything from 5W30 to 75W90 can be utilized. If you keep rpms down and drive the truck sedately, 75W90 is the one to go with as it's thicker than 5W30. If you're constantly in the 3500+rpm range with your 2.3L I'd get the 5W30 oil. For info check out the link below and click on "transmission oil" https://www.amsoil.com/storefront/de...spx?zo=1447600

__________________
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!

desertrat

Ford puts Mercon ATF in Manual Transmissions and that is what is recommended. Other vehicles use ATF in manual Trannys too. Use what the manufacturer recommends. Look it up in your book and dont do otherwise. If you want to flush it, then do so with Mercon, Drain, refill drive 10-15 miles, then drain and refill it again. Then run a hundred or so and do it again. That should do it. Watch for leaks closely. Someone may have put heavy oil in to slow down a leak. Generally, the thinner the oil the better lubricity, if it is the right application.

Milehog

If it calls for Mercon then use it. Gear oil has it's place but sometimes the engineers that design transmissions actually know what works best in their designs.
There are exceptions though. For instance, ATF works best in many guys Harley primary chaincases though the Harley marketing guys want you to buy something more expensive from them.

Jethro Bodine

contrary to popular belief, thicker is not always better with oil. In fact, it provides less protecton if the clearances were designed for thinner fluid as it resists being pumped through the engine/gearbox/whatever and does not circulate as it should.

I drag raced mustangs and built hot street mustangs for a while and never broke a trans running dextron III in the T-5s like they call for. I would drain out the gear oil and put the ATF in it if I were you. It'll probably shift better and get way better gas mileage. If there's a bunch of crap in there, flush it with diesel fuel then with ATF, then fill it up with ATF. Lots of foriegn cars and trucks actually use 30W or 40W motor oil in the gear boxes as you can not get ATF in some places. 90W is WAY thicker then Mercon/dextron 3 which is about 15W if I remember correctly.

Milehog

FWIW gear oil viscosity is measured on a different scale than motor oil.
90 wt gear oil is approximately equal to 40 wt motor oil IIRC.