MT or AT? If you're an MT, try a different fluid weight. The metal in the gearbox can tolerate some pretty high temps, but the gear oil cannot. Redline makes some good racing gear oil. Same goes with the diff.
If you're an AT, your tranny is already water-cooled by engine coolant. You can try upgrading to beefier radiator. There's a racing team that posts here and is sponsored by getbmwparts.com that uses a twin core radiator. They do endurance racing so they need something that ridiculous. They also use a high flow water pump I think with the stock thermostat.
'06 Arctic Metallic 325i | Sport Package | 6MT | Dinan Stage III suspension | Dinan exhaust | 330i manifold swap! Click here!
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Last edited by e90pilot; 07-22-2011 at 02:24 PM.