When overheating occurs only at high speed, cooling efficiency is below par. Possible causes are :
1. Clogged radiator.
2. Weak water pump.
3. Bad thermostat.
4. Clogged doolant passages.
Get the radiator checked for clogging, which is the most common cause for such symptoms.
Saturday, December 4th, 2010 AT 12:42 PM