Also, do not run the car without the thermostat. The thermostat has not only blocks coolant flow to the radiator when the engine is cold but also blocks off the radiator bypass when the engine is hot. Without the thermostat, only about half of the hot coolant coming out of the engine will go to the radiator, the rest will go through the bypass circuit because the thermostat will not be there to restrict the coolant from going through it.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

thanx, i put a new thermostat on it

Tom,

Too many variables.

Run the test you just did - heating engine up to 100-120, then turning heater on.

Do not use acceleration (higher fan speed) to drop temp, use heater only.

If temp drops when you turn on heater, you need to flush or replace radiator.

Do run a search here if you decide to flush, as, although I most often try most economical solution first, I seem to recall a lack of full success in flushing by some folks ... at least I picked up enough negative impressions that I decided to simply replace radiator - which is not that difficult on these cars.

thanx Kermit, the problem was the fanclutch , thanx for all your info, i have another issue... the car idels up and down at about 500-1000 rpm only sometimes, hot or cold dosent matter, the check engine came on , i got 2 codes (first) "Hot film Mass airflow sensor" code and a(second) " O2 sensor code(before cat)" i am thinking it might be the voltage regulator that is causuing this and it;s giving me these codes,... what do you guys think?