96 Chevy Truck Overheating or Thermostat?

My '96 Chevy CK 2500 4WD dashboard temp gauge starting showing fairly quick rises in temp to about 250 and then falls back to 180. The truck isn’t run that much – once a week or so. It has a slow coolant leak and a head gasket that should be replaced. Even after filling with new coolant the Temp rises after about 20 - 30 minutes on the road. Should I try something like Barr’s Leaks or could the head gasket be the cause? Don’t want to overheat & blow the engine. Thanks.

The thermostat may be sticking. Or, the engine cooling fan may be coming on late. Why? Is the engine coolant temperature sensor sending a cooler-than-actual signal to the engine computer? If coolant is leaking out, air is going in. The thermostat and the coolant temperature sensor don’t work so good in an air pocket, instead of in liquid.

It has a slow coolant leak and a head gasket that should be replaced…could the head gasket be the cause?

Yepper. If you have a gasket leak from the combustion chamber to the water jacket, hot combustion gases can be forced into the coolant passages. Coolant can then also go into the combustion chamber. When you shut down the motor, the residual pressure in the coolant passages can force liquid coolant into the cylinders where it runs down past the rings and into the crankcase. Over time, this is not a good thing to have occurring. You answered your own question and bandaids like Bars Leak is not the solution. Assuming you’re right about the head gasket. Easy enough to test for combustion gases in the coolant.

Thanks for the info.
I’ve been putting off the head gasket job & wondering about how much it might cost.

It may be the head gasket; but, I would expect the temperature to go up, and stay up, if that were the case.

I wouldn’t put the headgasket job off. As the combustion gasses blow throuth the breech they erode paths in the head and block surfaces, creating even more cost and work to correct the problem. And, the bigger the paths get is the more loss of ability to prevent overheating due to hot gasses being blown into the water jacket, the more coolant that gets drawn into the cylinders with every intake stroke, the more variation in temp you develop in the head (hot spots…warpage!), etc. etc.

Continuing to run with a blown headgasket causes the problem to worsen.

Since the cost is largely labor, and rates can vary greatly (if you’re in NYC you’re in trouble!) then you need to get some estimates.

Coolant leak, now there’s a clue.

How did you come to the conclusion the head gasket is leaking? How long have you been driving this vehicle with the alleged head gasket leak?