BenzWorld Senior Member
Date registered: Jan 2005
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RE: Normal operating temperature ??? 450 SEL
The main thing to watch,and this is Mercedes own reccomendation,is that in heavy traffic the guage will reach the top of the scale around 200*F .BUT,IT SHOULD DROP as soon as the car moves fast enough to have cooling air through the radiator,I find this happens immediatly.If it stays in the upper end of the scale all the time you have a problem.Start by going to a radiator shop.You have to get a "breath alyser " check to ensure that no head gaskets are leaking,then get the whole system reverse flushed.replace the coolant with the correct mercedes stuff.Don't waste money by pouring in generic antifreeze.
while you are getting the system flushed,ask the rad shop to check the fan belts.if they are looose- the pump will not be working .
The cap should be tested to ensure it's not leaking.These cars run at a high pressure,if the pressure is leaking,you will get a hot running condition.For every pound of pressure ,you get a drop in temperature.
The correct Mercedes cap is the ONLY ONE to use.
It's marked with a "100".
Finally,get the rad shop to do a pressure test to ensure there are no pressure leaks.
Thermostats sticking are sometimes a problem,but it's rare.
If none of the above is successful,get the igniton timing checked to ensure it's on the button.Ensure the trans is not slipping,the cooler is in the bottom of the rad. and it will heat the water very quickly.