100 degrees is not particularly high as most modern engines run quite happily between 90-100 degrees.
More importantly is the cooling system losing coolant? carefully check the coolant level after the engine has been off for at least 10 minutes. A modern cooling system should require hardly any topping up. If the level is low then you need to find the cause of the leak. It could simply be a loose radiator hose clip or more seriously the radiator is leaking. The worst case would be that the cylinder head gasket has failed in which case you may be able to see water mixed with the oil on the dipstick.
You do not mention whether the electric cooling fan can be heard running when the temperature rises? The fan should operate when the engine is idling in traffic and the temperature creeps above 100degrees. If the fan is not running under these circumstances then you need to check a. the fuse for the fan b. the electrical connector to the fan c. is the fan siezed? sometimes the fan bearings seize due to lack of use.
Dann
August 2007