# Auto Trans Fluid in a Manual



## Lordwacky (Jan 28, 2009)

Hey Guys quick question. I was talking to DIY guy a couple years ago and he mentioned that he changed the gear oil in his manual to automatic transmission fluid to save energy. He said you don't have to worry about damaging the transmission because you are only traveling 30-100 miles a day.

My question is, Has anyone else done this before? and what type of ATF would you recommend if that is the case?

thanks


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## jackbauer (Jan 12, 2008)

My bmw e36 uses auto trans fluid in the manual gearbox. Its actually specified by bmw!


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## etischer (Jun 16, 2008)

You could go with a synthetic manual transmission fluid, I'm using Redline MTL. It has the viscosity of ATF. It has made every transmission I've used it in noticeably quieter. 

Transmission fluid needs to allow some friction for the synchros to work properly.


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## DIYguy (Sep 18, 2008)

Like Jack, my manual trans also specs auto trans fluid. I do use a synthetic version.


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## tomofreno (Mar 3, 2009)

I'm using Mobil 1 LS 75W-90 Synthetic Gear Lubricant. The specs for it and Redline seem about the same to me. Anyone know how AT fluid differs from these?


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## DIYguy (Sep 18, 2008)

tomofreno said:


> I'm using Mobil 1 LS 75W-90 Synthetic Gear Lubricant. The specs for it and Redline seem about the same to me. Anyone know how AT fluid differs from these?


Most ATF's are between 0 and 20 W viscosity index. Your gear oil is 75W so...much thicker.


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## EVfun (Mar 14, 2010)

tomofreno said:


> I'm using Mobil 1 LS 75W-90 Synthetic Gear Lubricant. The specs for it and Redline seem about the same to me. Anyone know how AT fluid differs from these?


To my knowledge all synthetic Mobil gear oils are GL-5 rated. Redline MTL and MT-90 are GL-4 rated. Manual transmissions may not shift as well with GL-5. Some older manual transmissions with bronze syncros may be damaged with GL-5. GL-5 is not an upgrade to GL-4. Some newer manual transmissions are specced to use GL-5, most older unit are not. 

My Buggy has been running Castrol Syntac 0W-50 synthetic motor oil. I will be switching it to Redline MTL because that stuff has made every other gear box I've put it in shift very nicely.


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## electric85 (Apr 10, 2008)

like posted above use redline mtl, or i say go with royal purple synthetic, keeps your gearbox quiet, cool, smooth and will save energy...any good synthetic will


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## TigerNut (Dec 18, 2009)

Some manual transmissions, especially older ones, have plain bearings between the gears and the shafts; these would typically use a gear oil like 80W-90 or 75W-90, either petroleum or synthetic based. Other transmissions (like the World Class T5 and a lot of European or Japanese gearboxes) have needle bearings between the gears and the shafts, and they are specified to use ATF. While using one lube in a transmission originally designed to use the other may not do immediate damage, if you do extended operation at high speeds or high loads, you will notice premature wear.

Although a large proportion of manual transmissions are splash-lubricated, some manual transmissions (like Rovers) have a built-in oil pump; running these on gear lube is a bad idea because the pump is designed with the viscosity of engine oil in mind.

So, unless you know better than the gearbox designers, you should probably at least run the same type of fluid as what the factory calls for. You can experiment with grades and synthetic vs. petroleum based and likely do little damage, but if you go way outside the original spec then you might end up stuck beside the road at some inconvenient point.


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## ElectriCar (Jun 15, 2008)

Tom what does the owners manual spec? 75W is pretty heavy oil for a transmission AFAIK. You can check Amsoil.com and it will tell you the correct oil type to use. 

I can tell you if it's a T5 World Class, ATF is recommended. I think the Non WC is recommended to use something else. I use Amsoil's Synchro Mesh I think it is. That's what's in my S10.


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## EVfun (Mar 14, 2010)

Gear oils and motor oil viscosity are rated differently. It's confusing, but I found a page to explain the difference pretty well. I don't know if it is perfectly accurate, but the numbers are typical compared to other reputable sources. 

If your EV is not long range or if you almost always make short trips you should be fine running a slightly thinner oil than recommended, unless you live in the desert. The reason is that cold oil is thicker and the gear oil is rarely getting fully warmed. I would generally recommend Redline MTL as it has made everything I've put it in shift better.


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## tomofreno (Mar 3, 2009)

> Tom what does the owners manual spec?


I checked the Suzuki shop manual and it says 75W90 GL-4. I guess I didn't check the API rating on the bottles when I bought the Mobil. A couple days ago I drained the Mobil after heating the transmission for about an hour with ceramic heater, and replaced it with Redline MT90 75W90 GL-4. The Mobil looked like new, very clear and clean. I haven't noticed any difference in transmission noise (still noisy) or shifting.


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