I just bought a 1999 suburban, 147,000 miles. Temp gauge rises to 220 and falls to about 160 and holds there after the initial rise. Is this of concern? Do I need to change thermostat?. Coolant is at full mark in recovery tank however there is a lot of sediment in the tank... Radiator appears clean and full. Thanks for your thoughts.

 

It wouldn't hurt to flush the system and replace the antifreeze. The normal operating temp should be 195 and that is where 1999 runs at. You have to determine if you are actually running at 160 or is the gauge incorrect. Check the thermostat and see which one is installed.

 

If it is actually going up to 220, then settling at 160 and stays there, then it sounds like the thermostat is sticking shut and not initially opening as it should. A new thermostat should fix it. Be sure to get the correct temperature thermostat. Running too cool will affect fuel mileage and performance. Check the radiator hoses to be sure they aren't too soft, which will allow them to collapse and shut off coolant flow.