So I have a 2002 Chevy blazer 4.3L V6 2 wheel drive. The other day I was driving and I noticed that it was starting to overheat. It got up to about 220 degrees, which is not all the way up on the gauge but it's hotter than usual. Usually it runs at about 180ish, a little less than the middle mark on the gauge. When I stopped at home I turned it off and noticed that there was a boiling water noise coming from the coolant reservoir. After it cooled down I checked the reservoir and it was completely empty, so I added coolant to the fill line. Ever since then, whenever I drive for a while and turn the car off, the temp gauge will slowly go up to about 220 or 230 while the car is off. If I start it back up, the temp will slowly go back down to normal. This vehicle has never acted like this before. I got a radiator flush done yesterday and it's still doing it. This has NEVER done this before the other day after the boiling noise I told you about. It never overheats completely and it only goes up after I turn the car off. Any ideas?

 

Two things.

First, with a "closed system" with overflow thank, where coolant reservoir is unpressurized, if the "overflow" reservoir ever goes dry, once the engine is cold, open the radiator cap and top that up as well. If the system sucks air in when it cools down, you'll be low on coolant in the main pressurized system, and that can lead to more overheating. The system needs to be full completely in the radiator, and up at least to the 'cold' line on the reservoir.

Second, a weak or broken spring on the pressure cap can cause coolant boiling at operating temperature, leading to a loss of coolant and overheating. Either test your cap with a pressure tester, or just replace it. I usually just routinely replace my radiator caps every 2 or 3 years to avoid any issues with weak caps.

 

also your vehicle will warm a bit after you tun it off