91 MR2 N/A - question on which manual gearbox oil type / brand to use

brtsvg12 · 2025-10-13T13:23:23-0400

I recently bought a 91 N/A that is in flawless shape and in completely stock condition with 118K miles. It runs great with no known maintenance problems. I'm the 3rd owner and I have been reviewing the Carfax report and have been assessing what has been done with this car maintenance wise over the years. I would like to replace the gearbox oil as the 2nd owner told me the 2nd gear synchros are wearing, and it does make a slight grinding noise sometimes when shifting from 1st gear into 2nd gear. And I can't see that the gearbox oil has ever been replaced.

So, while the official Toyota BGB states to use ATF Dextron II type fluid, I see on this forum in past years that others have advocated or recommend using a GL-4 type fluid such as MT-90. Is this still current thinking for those of you that have used it and not used ATF per the BGB recommendations. Just looking for advice from those that have driven their N/A for a while now. Thanks in advance.

tabKola · 2025-10-13T16:22:40-0400

ATF was the original recommendation. GL-3, 4, or 5 75W-90 is the recommendation for 93+ transmissions and should supersede the ATF recommendation on old ones.

GDII · 2025-10-14T22:50:35-0400

I used Castrol VMX in my 1990 S54. Seemed to work fine and helped with a slight 3rd gear crunch.

Newdal_SW20 · 2025-10-15T00:30:01-0400

I've seen a lot of people having decent luck with MT-90. Although it's more expensive, it does have really good reviews for sorting out issues like this. However, if this doesn't sort out the grinding sound then you'd be looking at replacing the synchro.

SW20_Nate · 2025-10-15T10:01:10-0400

MT-90 is what I used in my S54, works great. That's what I use in my E351 now.

brtsvg12 · 2025-10-15T15:48:55-0400

Thanks for your responses. Upon digging deeper into past messages on this forum on this subject somebody mentioned that Toyota did release a service bulletin in the 93-94 timeframe that recommended using 75W-90 gear oil in lieu of the originally specified ATF for the 91-92 model years. So that's what I'll do.

GDII · 2025-10-15T20:21:56-0400

That will work well.

91 MR2 N/A - question on which manual gearbox oil type / brand to use

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