2000 Chevy Silverado normal operating temp is 210 , recently temp rises to 250. Its been this way for a few days, common operating temp is around 240-250 now, but does not overheat. Coolant levels are good, water pumps does not leak, and the thermostat appears to be ok, I am getting hot air from the heater.

Could have an air lock in the system or a sticky thermostat.

Cooling systems on vehicles are pressurized to allow the engine to operate at more efficient (higher) temperatures. This is accomplished by fitting a radiator cap that allows the pressure to build as coolant heats up. You can check the pressure imprinted on your radiator cap to determine what the boiling point will be. At 10 psi of pressure, the boiling point of water is 240 degrees F. At 15 psi, the boiling point is 250 degrees F, and at 20 psi, the boiling point is 260 degrees F. So your engine running at 210-220 is probably within the design specifications of your engine.

I think I answered this already, but just because you installed a new thermostat does not mean it is good. Sure sounds like a thermostat issue.

the radiator should be a uniform temp if there are cool spots, you have blockage. start looking there.

do you have a distributor on your truck you might want to replace the cap and rotor button. I would also get some throttle body cleaner and clean the butterfly valve use a papertowel to clean around where the valve wipes the sides it can get stickey and you will have slow response there is an electronic sensor tps witch moves with the petal and controlls everything for acceleration. you should also check your pcv valves they are little rubber hoses that goe from your valve cover to the air intake . I have a 2006 silverado and the temp gauge was bad make sure after about ten minutes the engine should be around the 210 or almost vertical if not replace your temp sensor located on the driver side under the brake master cylinder between the last two spark pluge it is brass in color and has a wire conector going to it . it will cause your truck to run cold and make it run rich and that will foul up your catalitic converter and all four 02 sensors cost me around 500 dollars to fix my self had to get through emmisions here in maryland well hopes this helps please leave feed back.

Hello there and thank you for choosing fixya :
To answer your question yes the temperature is normal for this vehical 205-210 is right at the normal range Normally you will have the 185-210 deg. thermostate installed in this vehical ''
You should notice that it does go up and you notice that it goes back down around the 210 degree mark this is telling you that the thermostate is working fine ok also if yo notice that it goes up and stayes up over the 210 -then you may have a problem this could be the thermostate may not be operating properly or the radiator may be clogging and needs to be flushed or your antifreeze mixture is not correct ok?
Hope this has helped you out
Best regards Michael

The thermostat controls the temp of the engine. The temp sensor tells the gauge what temp to display. If the heater is still putting out a lot of heat then it may be a false reading temp gauge. If however the temp is noticibly cooler then replace the thermostat. A stuck open thermostat would also cause the engine to warm up slowly. check for a loose/dirty connection at the plug on the temp sensor.

the engine is designed to operate at 210 to 220 degrees, so all is normal

With the truck running at operating temperature, squeeze your upper radiator hose. You may have to check it a couple times allowing time for your thermostat to open. Are you able to compress the hose a little when you squeeze it or does it remain stiff/solid? Your thermostat may be stuck open or even stuck closed.

It sound like either the cooling fan clutch is not operating properly or the radiator needs to be pulled and roded out by a radiator shop, 1 other thing, are you sure the temp guage is accurate? you can test this by using a scan tool on the engine control computer, tap into the ECT sensor for the injection.