I'm in Las Vegas. When I was in socal my 400+hp Z32 never overheated. Then last summer during 103 deg heat I decided to take my Z for a spin for once. I noticed that it was running warm, but did not overheat. Temp guage was couple of notches above normal. The Z has upgraded mishimoto radiator. So I just installed a set of hood vent, and waiting on a nismo low temp thermostat to go in before next summer.

This has me wondering. Bought a 2003 CL55 couple of months ago from socal and these cars are prone to heat soaking as well. Anybody in hot climate like Vegas, AZ, TX did you have issues running your AMG on stock thermostat? If you got low temp thermostat what was your experience with it?

From my general understanding of cars, this is not usually a good idea, as the ECU expects the engine to reach X degrees, and will change the fuel ratio until the desired operating range is reached. Putting a cooler thermostat in can (depending on the car) cause your ECU to constantly make your car run rich in an attempt to "warm up" to it's desired temps. Heatsoaking is more of a result of your other cooling system, the supercharger and its intercooler and pump. The pumps are known to go bad, and the stock heat exchanger is "good enough." Replace the intercooler pump and (maybe) intercooler, and split the system if you're worried about heat soak... Swapping the thermostat would be the last thing I would do in an otherwise stock car, especially a car engineered by Germans.

I replaced the pump in my car in about an hour, get some hose clamps. Made a huge difference in power loss over multiple accelerations.

Appreciate your response.
I have PB5 cooling split kit ready to go in. But I found the expansion tank had seepage from front two plastic tube so waiting on that. I will have those two things done this weekend. CL will stay mostly stock because I do not want the mod bug to take over like it did with Z. I no longer race like I did 10 yrs ago so stock power on CL55 is good enough for me.

I keep hearing about upgrading intercooler pump. Is bosch unit better flowing?

It's considered superior (I believe in flow) to the factory Bosch unit, which is the one that's known to fail (higher revision number on an assembly that otherwise looks identical). The superiority of the Bosch pump as opposed to other units has been debated in many threads... There are certainly other options, but I just went with OEM. I disassembled the outgoing pump, and a metric ton of what I assume to be carbon fell out of the motor (which is magnetically coupled to the coolant pump).