ATF instead of 75W80 GL5?

[kilou]

Hi,

my car manual transmission calls for a 75W80 GL5 oil (GL5 is important!!). I've renewed the oil several times and also the shifts are perfect when hot they are terribly stiff when cold. I know that many people with manual transmission calling for GL4 oils went with ATF (like Redline D4 ATF) with better cold shifting due to the lower viscosity. Redline website mentions that most of their ATFs meets GL4. My question therefore is:

- is there any ATF out there with an EP additive package that meets GL5? Bonus is that I need special EP additives (non borates) that are not corrosive for brass synchros (this is what my box has).

- is there any long term danger in substituing a 75W80 GL5 with a n ATF that would meet GL5??? I know that ATF is slightly thinner but this is what I'm looking for to improve cold shifting. However when hot a 75W80 (8.5cSt) is pretty close to an ATF (7.5cSt)....so it should be ok no??

Thanks a lot for your input

 

[ConfederateTyrant]

I don't think the GL-4 rated ATF has enough load carrying capability as a GL-5 gear oil. For that I'd suggest staying with a gear oil of that same viscosity.

 

[Quest]

I'm not aware of GL-5 rated ATF to begin with.

Q.

 

[Whimsey]

Not sure but maybe one of the syncromesh MT fluids from RP, RL or Amsoil might fit your needs for cold weather shifting and meet your MT needs better than ATF.

Whimsey

 

[kilou]

Thanks for your replies guys. It's true that I have not found any ATF rated GL5 and it seems that all the synchromesh fluids available only meet GL4. The only fluid that may work would be Redline Lightweight gearoil which is a GL5 but then it doesn't have a lower viscosity as my current oil (which is 45cSt at 40°C and 8.5cSt at 100°C). Couldn't find anything lower than 45cSt at 40°C with a GL5 rating for now but this is what I probably need to have a smoother shift when cold...

 

[unDummy]

What transmission? What gear oil brand/product are you using?

The viscosity curve in a fluid slopes upward quicker with a mineral vs synthetic as the temperature drops. A 40c temp comparison isn't anything to compare with. Too bad that manufacturers don't list 0c or -20c specs. A full synthethic should perform better(less gradual slope change) as the temp drops even if the hotter temp visc's are identical. For example, 2 identical ~7.2cst ATFs at 100c could have a 10000 difference in visc @ -40c!!!!

A 80wt fluid needs to be between 7-11cst. You can thin the lightweight with the superlightweight 50:50, with the added bonus of using a full synthetic fluid. This should be noticeable when comparing to a mineral 80wt, regardless of the paper specs.

When you require a GL5 gear oil, stick with ANY fluid rated GL5. This means ATF is a big no-no. Depending on the transmission family, the gl5 requirment might be simply what is available in the area. If the transmission family is used in multiple markets using other weights or specs, you might be able to find another spec(like GL4) which could open up more choices.

 

[sprintman]

'Redline Lightweight gear oil'. Is that MTL or MT90 or something different?

 

[MinivanMauler]

MTL is the lightweight 70W-80.

MT-90 is 75W-90.

Amsoil has a manual syncromesh fluid called MTF.

 

[aquariuscsm]

Originally Posted By: sprintman
'Redline Lightweight gear oil'. Is that MTL or MT90 or something different?


You`re probably referring to Redline`s Shockproof Light gear oil.

 

[aquariuscsm]

I`m also curious as to what kind`ve car you`re driving.

Listen to unDummy. He knows what he`s talking about.

My car requires anywhere from a 75W90 GL4-75W140 GL4 in its manual transmission via 1990-1996 Z32 FSM. I`m currently running Sta Lube SAE 140 GL4 (I`m in south Texas and it`s always hot here). My car absolutely LOVES that thick stuff. Shifts feel very cushioned and so smooth that when you move the shifter between the gears you can`t even feel them changing.

 

[double vanos]

FWIW I'm running Redline MTL in my Mazdaspeed 3 that calls for GL4 75w90. I just got tired of the low shifting crunch.

Since MTL is a 70w/80, I'm a tad out of grade. Well, at least the shifting is really good.

 

[kilou]

My car is a Volvo but it uses a geabox made by Renault (a french car manufacturer). This gearbox has an uncommon design (as some most french cars and some italians too) with hypoid gears in the box and this is why they MUST use a GL5 oil. They call for a 75W80 GL5.

My actual oil is kroon-oil SP1051 which is a synthetic 75W80 GL4/5 available in Europe. It has the lowest dynamic viscosity I could found: 20000 mPoise at -40°C. Even Redline MTL has a higher viscosity! So I'm looking at something that would be even better when cold...

 

[mechtech2]

kilou - It seems that to get the protection you require with that hypoid gearset, you are stuck with thicker oils.
ATF is not an option for you.

 

[kilou]

OK I forget the ATF then. However UnDummy came with an interesting point with mixing Redline Lightweight with SuperLight gearoil. Both are GL5, lightweight is a 75W80 (similar to my current oil) and Super lightweight is a 70W/75W. The viscosities are as follow:

- Light weight: 500 Poise @ -40°C
- Superlight weight: 1400 Poise @ -55°C
- My actual oil (SP1051): 25 Poise @ -40°C

As you can see my current oil (synthetic) already has a very low dynamic viscosity, much lower than the Light weight!! The dynamic viscosity of the super light is expressed for a temp of -55°C so it's not comparable. From these readings, is there anything that would suggest that a 50/50 mix of Lightweight with Super lightweight would achieve a better (ie lower) dynamic viscosity compared to my current oil?????

That was the question about dynamic viscosity but is this really the only factor that will determine the shiftability when cold?

Is there any danger in running a mix with an overall viscosity when hot lower than the one of my current oil (8.5cSt at 100°C)???

Thanks!

 

[MolaKule]

Quote:
Is there any danger in running a mix with an overall viscosity when hot lower than the one of my current oil (8.5cSt at 100°C)???


Yes, accelerated wear if you have a hypoid gearset. In your case you need a hot temp oil film with a weight not less than a 75W for the hypoid gear set and a GL5 additive protection to protect the highly loaded teeth of the hypoid gear set. Oils will shear to lower viscosites so I wouldn't sweat the brookfield viscosity.

I question the Brookfield viscosity of your oil.

An alternative is to use something like RL MTL, Amsoil MTF, or GM SYnchromesh and change often.

It almost sounds as if the SP oil has an ATF-like viscosity with a GL5 add pack.