Or this kit

http://store.vacmotorsports.com/vac-...kit-p1446.aspx

yep definitely an option, and cheaper:)

What happens to the oil pressure when you fit a cooler which is much bigger ?

Depends on various things, design, pipe diameter etc etc.

There will be an effect yes, so going with a tried and tested researched unit is paramount. Some coolers will have negligible effect on pressure, others will drop it too much.

As far as I know the factory oil cooler doesn't have a thermostat.
Putting a bigger cooler (more efficient) will definitely drop the temperature which is a good thing when the car is used in a racetrack.
In all other situations (motorway) I am sure the oil temp will be quite low, especially in countries that it's not so hot.
Adding here the oil pressure drop, I think this upgrade will create more problems than it will solve.
So I believe it's a good upgrade if you are using the car only for trackdays and nothing else.

Thermostat is fitted in the oil filter housing, I have removed mine and replaced with a oil diverter valve........allows 100% of the oil to pass to the cooler 100% of the time....

similar to this

http://store.bimmerworld.com/e36e46-...alve-p980.aspx

Oil pressure will remain the same with a bigger cooler, you will just increase the oil capacity of the engine. But not by much. ie depends on cooler size over OEM.

For most I would not advise this. Much better to retain standard stat for road and track use. I'd only consider diverter for race application.

The big cooler I use has the same dimension pipe internals, connections, etc. so oil pressure is not affected. Only difference is a slight drop in oil level after dealer oil changes. This is only noted after full warm up with thermostatic valve opened. About 1/2 litre extra required to maintain correct sump level AFTER the cooler circuit has opened.

My interim oil changes at Simpson's include a run to warm to temperature, re-check level and top up to account for it.

Does the oil in the cooler drain out when changing the oil Alex?

I'd heard that some coolers retain their oil when it's dropped during a change????

( forgive me if that all sounds stupid- but what do you expectfrom me!?!)

I think some might be retained Jim. But, every oil change since I've changed requires just under 1/2 litre over normal capacity.