I don't trust myself playing with numbers in aircraft conf files .I have a Piper twin engine and even with the cowl flaps closed it runs way too cold . How in the conf. file do you plug numbers in so you have more realistic engine temps? Louis cyyc 

You would need to change the values in the air file, assuming the gauge is even reading sim values.  Some custom gauges don't and so in that case, it probably wouldn't make any difference.  Convert the temperature to R, then scale it appropriately.