Diff Cooler - The Unofficial BMW M5 Messageboard (m5board.com)

WillM5 · 11th June 2009, 20:58

Hey guys Im rebuilding my diff right now and I wanna plumb in a cooler using a turbowerx oil sump pump and an aluminum oil cooler. My only concern is the size of the cooler. For packaging reasons I want to use a smaller cooler so I can tuck it in the wheelwell. Im thinking about using a 6.25x4.75.2 core for my diff. Any ideas as to if it will be enough for it ?

Im using this pump for it.

Exa-Pump®

The drain plug and fill holes are M22x1.5 threads, so im gunna use an adapter plug that has an AN flared thread on it and use the drain as a supply port and the fill hole as a return port. Im just curious if the small core has enough surface area to effectively cool the diff down. And also if the diff input shaft will be starved for oil by the sump sucking oil from the drain plug. That could be rectified by filling the diff slightly more than usual, just so the input shaft bearing always has a constant submersion with oil.

I just had my factory diff go on me and I do beat on it alot, ex. hard launches, high speeds, rapid acceleration and hard braking, so its a good idea to have something to cool the fluid, I really dont want to have to go thru this again and I always love having peace of mind about my components. This is a peace of mind mod more than anything.

Stevie · 12th June 2009, 02:23

The idea is fine, you've just got the hoses the wrong way around. I suspect your idea is to skim hot oil off the top and feed cool oil from the bottom.

That's not going to fly.

The diff might be filled to the top plug when stationary, but it looks like the inside of a kitchen blender at speed. The top oil is going to be as much air as oil as the oil will be filled with bubbles, so you'll really need to use the diff housing as a sump and extract oil from the bottom. That way your supply is reliable instead of running the pump dry every time gravity throws the oil the other way and having a cavitating pump after a high speed run causing some foam. The risk of the cool oil entering the diff and going straight down to be cooled again is nil as there's a nice big bit of metal with theeth going around in there mixing things up

On a sidenote: have you ever measured temps in the diff? Been driving a friends Alpina recently and it actually takes surprisingly long on his gauge to heat the diff anywhere beyond 80 degrees C. Must admit his driving is usually at reasonable speed. For being sideways that is.

Ferrari-Bmw · 12th June 2009, 19:30

Quote:

Originally Posted by Stevie

On a sidenote: have you ever measured temps in the diff? Been driving a friends Alpina recently and it actually takes surprisingly long on his gauge to heat the diff anywhere beyond 80 degrees C. Must admit his driving is usually at reasonable speed. For being sideways that is.

Good point..

On a highspeed run in EU i have never been above 80°c in my BT

I have a temperatur gauge on my CABRIO and after 2 rounds on the Nordschleife the diff is 105°c

on 160 km/h + ... steady and more on the AUTOBAHN (( outside temp 20°c or more)) i see often between 90 and 100°c

oilcooler is a brilliant solution if you are going sideways ,, ALOT and often

the heat in a diff under that circumstandes is tremendeous,, if the action is long and wild

Eku · 12th June 2009, 21:20

Hello

E30 M3 A-group race cars used pumps that has belt from another drive shaft to oil pump. (just like altenator). Maybe good for a race car. Are you goin to use pump all time or just when oil gets hot?

Eku

Stevie · 13th June 2009, 00:40

Older Alpina's like te e12 B7 turbo used that same solution. Belt running off the driveshaft flange. I suppose it was a nice solution 30 years ago......

Quote:

Originally Posted by Eku

Hello

E30 M3 A-group race cars used pumps that has belt from another drive shaft to oil pump. (just like altenator). Maybe good for a race car. Are you goin to use pump all time or just when oil gets hot?

Eku