550 overheating

My 550 has always run hot, compared to other cars. On track days in summer it has hit 110-120+ degrees C (250 F), which is supposed to be the limit allowed. When it gets this hot I usually short shift for a lap or two and the temps come back to 90-100 and I get back into it again.
Even in daily driving in slow traffic it regularly sees 110, before the fans kick in and bring it back to 85-90 (185-195F), even with ambient temps of around 10 degrees C (50F).
Tonight I took out my pyrometer and brought the car up to temperature, with the gauge showing around 100 C (212F). I then reved the car to around 2500rpm and while the filler lid was off measured the temp of the water with the pyrometer. I revved the car, so I would be measuring the temp of the water from actual engine, rather than just the heat of the water in the in the water overflow (I'm sorry if that doesn't make complete sense).
The pyro only measured 80 C (176F) when the temp gauge was reading 100 C (212F).
My question is, does the water cool that much from the time it reaches the temp sender to running through the overflow/filling container or is my temp gauge or sender spitting out garbage?

 

That's why I was asking, to find out if the water in the header tank was significantly cooler than the temperature of the water at the temperature sender. Having a look at the cooling circuit, it does not appear to receive it's flow from "cooled" side of the radiator circuit, infact it is plumbed in between the inlet and outlet of the radiator as well as the inlet and outlet of the water pump. It is definately worthwhilehaving a look at the thermostat and water pump though.

 

Thanks Bruce, you saved me a bundle, the alarm has been trouble free since!

 

Finally tracked the problem down. It turned out to be a faulty temp sender under the intake manifold causing the thermo fans to come on too late.

 

Ernie
Close, but no cigar, Bruce just cut and pasted a portion of Phil's earlier response.