Where is the thermostat on a 200 GMC yukon - 2000 GMC Yukon Denali

First stop, the manual. I have a 2003 and it runs a bit over 200

under the hood I would check the thermostat to make sure it open so that the hot antifreeze reaches the sensor to make the fan start

195'F thermostat

I would estimate the part is about 200. Usually there is about a 75 dollar fee for installation. Muffler shop would be keeping old one as part of price.

follow the top rad hose at the end where it conects to the moter is a sleve held on by two bolts the thermostat is in there

Two things come to mind. One would be the cooling fan running all the time, The other would be the thermostat opening too soon. You can observe the cooling fan while the vehicle is idling with the hood up. Give it time to warm up to the 200 mark and see if the fan comes on and stays on. If it does, then the thermostatic fan relay will have to be replaced. If the fan is functioning properly, then i would change the thermostat.

Could have been an air lock that worked its way out. Did you add any coolant prior to driving? Keep an eye on it, another thought could be your thermostat stuck closed and then opened. Is it normal to run at 200? or 160? Perhaps the weather was extreme which might cause the sudden drop.

You tried a flush and fill? Check your water pump. Look close at it with engine not running to see if any water is coming out of the weep hole which is underneath. Sometimes you can tell if it is bad if any noise is coming from it. Also the propellers may be worn out or broken which either case it will cause overheating. Buy yourself a repair manual at the auto parts store and read up on it if you do your own work.

Not true,Although,it is located in the pump,You don't need to replace the pump if the thermostat is replace.See pix