Egine temperature gauge fluctuates between 80 and 100 on 2003 Mercedes-Benz S55 AMG

When I was driving the car during the winter there were not any problems with the engine temperature gauge as I had the heat on. I replaced the thermostat three times, in case that is your answer. During the summer, when I have the A/C on then I see the engine temp gauge go from 80 to 100 at idle, then when I start driving again it takes awhile for it to go back down to near 80 degrees. I am wondering if the elctric fan is bad, although I think I hear it coming on. When I turn the heat on then the temp goes down, this made me think that it was a head gasket or cracked head however, Mercedes of Annapolis checked this and they did not see any leaks, etc. They recommended checking the fan and doing a full diagnostic. However, if I can do this myself I will. Any help will be appreciated. Thanks

Asked by for the 2003 Mercedes-Benz S55 AMG
If you want to do this yourself, then determine when the fan is supposed to come on (what is the engine temperature for low speed/high speed fan operation) and check the engine for signs of a headgasket leak. Check the radiator for proper flow and water pump for proper operation. Some of this takes special tool and you definitely need a very good repair manual to get the needed information.
One more thing, verify that the engine temperature is actually fluctuating, this could be a sensor or gauge issue.
It is not a head gasket or cracked head as I stated that Mercedes already checked all of this and all came up clean. The temperature gauge does go back down to 80, but it takes awhile. Therefore I assume that this is a electric fan issue that is not coming on when it should. I have also replaced the thermostat three times, so that is not it. The problem may lie in the fan as the head gasket, coolant, radiator, block, etc were all checked and are operating fine. I am trying to figure out why during the summer that my engine gauge reads between 80 and 100, which is not bad as it is not over heating. I need information on checking the eletric fan that cools the radiator. Is this a battery issue, or is it a electrical issue, etc and how do I check it and fix the fan myself? It can't be that hard to check and fix myself.
I have the same problem. Did you fond the problem?