Astra H VXR Sprint

Over the winter I have decided to do something about the gearbox oil temperatures, which when on track can get seriously hot. One of the downsides of the M32 gearbox is its inability to deal with heat effectively. After fitting a gearbox oil temperature gauge I have been able to monitor the gearbox oil temperatures on the road and (mainly) on track.

Without a gearbox oil cooler the gearbox oil temperature on track days can quickly rise to 120+ degrees C (if you let them) when the car is driven hard which can degrade the gearbox oil quickly. On cruise on the road the gearbox oil temperature tends to sit pretty stable in the mid 70’s, but any hard use will again cause the temperature to rise. Because the M32 gearbox does not dissipate heat readily the only way to bring the temperature down is to stop the car and leave it idle for about 20 minutes or so, and the oil temperature drops to mid 70′s and then another 20 minutes on track will bring the temperature back up again and so the cycle continues.

Using a very high quality fully synthetic gearbox oil (75w-90) is essential and so are regular gearbox oil changes.

The addition of a gearbox oil cooler will keep the gearbox oil temperature under control when on track and from temperature monitoring on track is (I would say) essential for track use.  As far as the car is concerned on track the high gearbox oil temperature is the one thing that hinders its use, because everything else such as water temperature (Enlarged Pro Alloy Water Rad), inlet air temperature (Full Height Front Mounted Courtenay Sport Racing Intercooler manufactured by Pro Alloy, brakes (Alcon Monobloc 4 Pot calipers with 356mm x 32mm alloy belled discs) are absolutely fine and under control.

So fitting a gearbox oil cooler will require an additional oil pump and an external oil cooler matrix to cool the oil.

Also requiring consideration is the engine oil cooler. Having data logged the engine oil temperature on an Astra VXR race car producing around 280-290bhp the factory fitted water cooled engine oil cooler can keep the temperature under control.However further power increases will put additional strain on this.

So under consideration is also an external engine oil cooler in place of  the OE engine oil cooler which is a smaller water cooled laminova core, mounted to the rear of the block just under the inlet manifold and cooled by the engine coolant.

With the addition of a gearbox oil cooler, this then potentially means two external oil coolers (one for the engine and one for the gearbox), and the associated problems of where to mount them…..

Due to space constraints a plan came to light. The thought process is to use the original laminova core (originally the engine oil cooler) as a gearbox oil cooler because it can cope well enough with cooling the engine oil (which is a 5 litre capacity) and since the gearbox only has 3 litres of oil it should be more than capable of keeping the temperature under control. Also by removing the engine oil cooler and making it an external cooler, the thermal shock from the heat of the engine oil is being removed from the engine coolant. And when running on track the water temperature generally never exceeds 95 degrees C, which is a perfectly acceptable gearbox oil temperature.

So if I am adding an extra oil cooler matrix I thought I would make it for the engine oil and use a bigger external oil cooler because the car is getting to the limits of the factory oil cooler’s capabilities. By doing this I am then only adding one external cooler matrix (for the engine) and re-using the exiting engine oil cooler for the gearbox oil rather than having to add two external matrix (one for the engine AND one for the gearbox.)