I also live in Phoenix and have a 1989 260e which has the m103 engine and the cooling system is identical. A week ago I installed a Behr thermostat rated with a 79 degree celsius rating rather than the factory 87 degree. I bought it from an independent MB facility in Scottsdale. I don't believe it is available from MB. My car is running noticably cooler although it will still reach 105 C if sitting idle for prolonged periods. The part number is 100-200-07-15 e-mail me if you have any further questions. Tom