Cool manual trans with a new fluid or additive?

[Gearcruncher]

I have a BMW M5 with a 6 speed manual transmission. I take this car to the track, and on faster tracks, after 20-30 minutes, I get a warning that the transmission is getting too hot and the car reduces the redline of the engine.

The transmission does not have an oil cooler, and does not have a known way to add one.

I am running fresh OEM fluid in the transmission. Any pointers out there on if a different fluid or an additive would reduce enough friction to make a difference? Just getting me another 10 minutes would make me happy.

 

[MolaKule]

What is the 100C viscosity of the Speced fluid?

One thing you don't want to mess with is the fluids friction modifier.

Any further tracking may require a transmission cooler, since the transmission design and fluid was speced for non-track operation.

 

[Ramblejam]

As Mike Miller says...

http://www.redlineoil.com/product.aspx?pid=45&pcid=7

 

[abycat]

You could get a shop to drill and tap two holes in the appropriate spots and use a pump to circulate fluid through a cooler. Have the pump turn on at a certain temp. Would be consideratly less than a blown tranny. just a thought

 

[RooflessVW]

I would recommend you use a high quality synthetic fluid, check the link to Redline Oils.

The temperature circuit, I'm sure, can be fooled. That gearbox takes much more abuse in its other applications. Several high-horse E39s (F.I.) have no issues with transmission temperature or wear.

The E90/92 version of the gearbox does have an oil cooler installed from the factory, but I do not believe that there is a way to retrofit it to the E60 unit.

 

[bdcardinal]

Originally Posted By: abycat
You could get a shop to drill and tap two holes in the appropriate spots and use a pump to circulate fluid through a cooler. Have the pump turn on at a certain temp. Would be consideratly less than a blown tranny. just a thought

I bet he could just use the drain and fill fittings for the in and out lines on the cooler. Then use a Mocal pump and oil cooler. Some of the guys with Terminators that road race use a Mocal pump and then mount a stock supercharger heat exchanger on the rear bumper.

 

[eljefino]

If the transmission has cooling fins cast in there may be a way to rig a fan up. Think of a hopped up CPU cooler.

Are all the splash shields and underbody thingies still properly attached?

 

[Olas]

Originally Posted By: bdcardinal
Originally Posted By: abycat
You could get a shop to drill and tap two holes in the appropriate spots and use a pump to circulate fluid through a cooler. Have the pump turn on at a certain temp. Would be consideratly less than a blown tranny. just a thought

I bet he could just use the drain and fill fittings for the in and out lines on the cooler. Then use a Mocal pump and oil cooler. Some of the guys with Terminators that road race use a Mocal pump and then mount a stock supercharger heat exchanger on the rear bumper.


This.
Using the drain plug and fill plug as feed and return for the cooler is a known and accepted practice.
Better fluid wouldn't hurt either.

 

[Jetronic]

is the temperature being measured, or calculated? if the latter, nothing will help besides flashing the software...

 

[Gearcruncher]

I dug through my records and I'm actually running Redline MTL in the transmission. It's a lot cheaper than the stock stuff (BMW MTF-LT-2 at $25+ a liter).

The transmission temp is detected by a sensor. I'm still tempted to just throw a resistor in and trick it into thinking the temp is 25 deg lower than it is, and then replace the fluid every year.

I'll climb under the car this weekend and see what can be done in terms of drain/fill fittings or other possibilities.

Thanks for everyone's input!

 

[MolaKule]

Originally Posted By: Olas
Originally Posted By: bdcardinal
Originally Posted By: abycat
You could get a shop to drill and tap two holes in the appropriate spots and use a pump to circulate fluid through a cooler. Have the pump turn on at a certain temp. Would be consideratly less than a blown tranny. just a thought

I bet he could just use the drain and fill fittings for the in and out lines on the cooler. Then use a Mocal pump and oil cooler. Some of the guys with Terminators that road race use a Mocal pump and then mount a stock supercharger heat exchanger on the rear bumper.


This.
Using the drain plug and fill plug as feed and return for the cooler is a known and accepted practice.
Better fluid wouldn't hurt either.

This would appear to be the least "Knuckle Damage" approach.

 

[Jetronic]

ever considered you have a case of thermal runaway? MTL is about as thin as Redline goes. For track use it would be prudent to go up a bit anyway. MT85 or shockproof light?

 

[Jetronic]

Ever considered you have a case of thermal runaway? MTL is about as thin as Redline goes. For track use it would be prudent to go up a bit anyway. MT85 or shockproof light?

 

[MolaKule]

I believe the stock MTL is like a 7.5 cSt viscosity fluid.

Going up any higher than the 10 cSt fluid in there currently is only going to raise temps, not decrease them.

Maybe try these fluids, which are ~ 7.0 cSt@100C:

Royal Purple's Synchromax

Ravenol MTF-2

Honda MTF

VW part number G052512A2

Pentosin MTF 2; sometimes denoted as MTF-LT-1, 2.

 

[dailydriver]

Originally Posted By: Jetronic
MTL is about as thin as Redline goes.


The Red Line MTL may be the thinnest actual manual trans fluid they make, but at 10.6 cSt it is still MUCH thicker than what that gearbox came with from the factory (a ~7.5 cSt fluid, as Mola Kule has stated).

 

[Jetronic]

I found a castrol oil (VMX80, iirc) with the BMW spec, it's an 80 aswell, like the redline. kv of 10+.

This leads me to believe the standard fill was an 80 aswell. In that case the redline isn't any thicker.

 

[zeng]

Originally Posted By: Gearcruncher
I have a BMW M5 with a 6 speed manual transmission. I take this car to the track, and on faster tracks, after 20-30 minutes, I get a warning that the transmission is getting too hot and the car reduces the redline of the engine.
The transmission does not have an oil cooler, and does not have a known way to add one.
I am running fresh OEM fluid in the transmission. Any pointers out there on if a different fluid or an additive would reduce enough friction to make a difference? Just getting me another 10 minutes would make me happy.



Originally Posted By: Jetronic
ever considered you have a case of thermal runaway? MTL is about as thin as Redline goes. For track use it would be prudent to go up a bit anyway. MT85 or shockproof light?


Thermal runaway ? ..... very likely.
I would even consider replacing with a 75W90, RL or any others.