mk3 transmission question/ tire question..

[rohin02]

Ok ive got a 91 mk3 auto turbo supra, wondering if i shud just use DEX3 or any sorta synthetic tranny oil? anyone know what would be the difference in running syn or just regular dex? i work at a lube shop so im doing it my self i just wanna know what fluid i should be using, secondly my friend has been telling me to get wider tires like 9 width or something should i or shouldnt i i currently have like 6' or 7'. thanks for reading

[MA70-3.0GT]

On the trans side, I'd say just stick to what's recommended (dex3 for the auto). As far as rubber goes it's up to you really & what you want to do. For normal road use the stock 245/50 16" should be fine, I think any wider than 255 requires arch mods anyway though I could be wrong (my car on 245/40 17" is "one-finger-close" as it is!)... For what it's worth just spend the extra you would've put to wider wheels & tyres to higher quality ones & you'll see more difference in handling that way for less hassle.

[cre]

Wider tires = more rolling resistance. Don't go wider than you actually need and absolutely do not go wider than your rims will support without distorting the sidewalls! I don't recommend any wider than 235 on a 7" rim.

As for the transmission fluid Dexron VI (that's Dex 6 NOT 4) is supposedly cross compatible and has better hydostatic properties and generally runs cooler. I would verify this first though and flush thoroughly before converting. You'll need to further research this though, I haven't dealt with this myself.

A REAL synthetic of either type of fluid will provide more consistent viscosities at various temperatures, definitely a good thing if the car is driven hard.

With a transmission fluid change on a high mileage car I recommend installing an inline filter at the return from the cooler. The fresh detergents are going to free up a lot of crap that's accumulated over the years. Change the filter after a couple months and then once every 10Kmi to 20Kmi thereafter.

[Bill UK]

I didn’t have good result with Dexton III, I did a fluid/filter change only to find the local autoshop only stocked Castrol ATF TQ dexron III, so assuming this would be a better advanced product, I filled her up. As soon as the transmission had reach normal operating temperate there was a loud buzzing noise coming from the box. I contacted Castrol Tech Dept and they confirmed that Dexton III is a GM fluid, and not meant for the A340 boxes. Managed to find some Castrol TQ-D which is dexron II and did another fluid change, that was 3 years ago and I haven’t had a problem since.

[cre]

I really think your problem was more likely due to other causes... contamination, internal leaking due to the slightly lighter viscosity of Dex III at lower temps or something along those lines... the more I read on this topic the more certain I am of it. Even Toyota calls for Dex III in place of Dex II..... and they'll probably call for the switch to Dex VI once III is declared obsolete.


There is a MASSIVE amount of info on all of this to be found through Google... more than I expected actually. What I've found boild down to this:

It's Dexron, not Dexton or Dextron and all Dexron formulae are GM's. GM superseded Dexron II (the ATF specified by Toyota for use in the A340E) with Dexron III and later are expected to supersede both with Dexron VI. Using anything else in place of these risks the introduction of emulsifying agents (makes it all gel and solidify) or creating a caustic environment (ie: you just mixed up a fresh batch of light acid), so be sure to read the datasheets THOROUGHLY to establish compatibility before you mix any transmission fluid. it only takes a couple drops in come cases. Chrysler's ATF+4 specification, for example, is "not compatible and may result in significant damage.". The original Dexron formula is also thoroughly incompatible with all others.

TQ-D is more of a middle ground between Dex II and Dex III, it isn't either but it is fully compatible with Dex II but does not meet Dex III's requirements. It appears that it's not available outside of Europe from what I've been able to find.

Shopping around online it appears that there aren't any manufacturers making a genuine Dex II ATF anymore... Of course I suppose that if a company was making it they couldn't legally use that designation as GM owns it and probably won't allow it to be used since it's a dead specification.

Dexron VI is supposed to perform MUCH better in cold weather environments due to an even more consistent viscosity than any other generation of Dexron.



Special thanks to: www.bobistheoilguy.com; jdub and his oil and lubricants section at www.supramania.com; www.google.com; www.castrol.co.uk; and Advil!

[cre]

Originally Posted by Bill UK

I contacted Castrol Tech Dept and they confirmed that Dexton III is a GM fluid, and not meant for the A340 boxes

Whoever you spoke to was asleep at the wheel. The A340E even came with a GM ATF in it.... Dex II. The only Toyota auto's I've found mention of that don't require some form of Dex are pre80's and those use a REALLY old Ford spec ATF known as Type F.