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The car is a 1977 450 SL. The engine temperature<br> gradually increases and tends to the high end of <br> safe operating range when the car is ascending long grades, and in city taffic. The car has a new mercedes radiator. The safety fan has been tested and works to specs. The fan clutch is <br> a rebuild, two years old. I do not hear the main fan kick in as temperature increases. How can I tell if the fan clutch is working? Any other ideas appreciated.
 

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The temperature sensor may be off, giving a high temp indication - may want to check it out.<br> <br> You may be able to get the car warmed up to where the fan kicks in by covering the radiator with cardboard. DON'T LEAVE THE CAR UNATTENDED AND REMOVE THE CARDBOARD AS SOON AS THE FAN STARTS OR THE HIGH TEMP IS INDICATED. You may also want to remove the cardboard and let the engine run a bit to cool down before shutting the engine off. I have not had to do this, but these are the steps that I would take.<br> <br> Stan
 

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I have a '73 450SL with the same problem when driving at higher speeds during the warmer times of the year. During the cold seasons, the temperature remains relatively normal. What are the steps required to troubleshoot this problem?
 

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I once bought a W126 300SE which had this problem

The garage said that sometimes the cooler (correct english?) gets cloged. They tried to clean it two times but ended up replaing the entire cooler.
 

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Re: Aux Fan Test

My 1988 560Sl run hot and I wanted to make shure that the Aux fan worked with out a great deal of work. There is a Simple Solution to see if the fan works! 1. Start your engine. 2. Locate the aux fax switch located on the thermostat housing. My switch is green with 3 connections. The connector that has two connections has to be pushed in to release it. 4. Disconnect it. Take a jumper clip and short the connector. The fan should be running if you are lucky. Mark
 
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