I have a 95 GMC K1500 pickup with a 305 TBI engine. It had a heater core leak for a while but was otherwise running fine. I swapped the heater core recently and topped off the radiator and overflow bottle. I drove it the other day (about 20 miles) and it reached normal operating temp with no overheating issues. After driving I checked coolant levels and found oddly that the overflow hadn't changed and the radiator was still full to the cap.
Today I took it a few miles down the road and the temp gauge started bouncing (quickly) into the red then back down around normal. I thought it was an electrical/ground issue by the way it was bouncing, so I kept driving. It went up to red, stayed there, then came back to 2/3 (hot), when I finally realized it was really overheating. The gauge was being very erratic, which is not normal. Since it was a short trip I was pretty much back home by now, I just cranked the heat all the way up (it was blowing hot air) to make it a few blocks home.
I opened the hood and found the top radiator hose (between thermostat outlet and radiator) was hot and the coolant inside boiling. I felt the radiator cap, which was cool to the touch, and felt the lower hose (radiator to water pump) and it was cool. Overflow bottle level is still at the cool mark and isn't boiling. Fast forward a few hours later, I open the radiator cap and the coolant is full to the top like it was before. I started the engine with the cap off and after a few minutes the coolant started surging out of the radiator, and the gauge was back toward 2/3 (hot).
I'm guessing I have either an air pocket or the thermostat just up and died. I changed the thermostat and water pump not too long ago. Any thoughts or suggestions? If I run it with the cap off to burp it the coolant surges out then goes back down.
Thanks.
Today I took it a few miles down the road and the temp gauge started bouncing (quickly) into the red then back down around normal. I thought it was an electrical/ground issue by the way it was bouncing, so I kept driving. It went up to red, stayed there, then came back to 2/3 (hot), when I finally realized it was really overheating. The gauge was being very erratic, which is not normal. Since it was a short trip I was pretty much back home by now, I just cranked the heat all the way up (it was blowing hot air) to make it a few blocks home.
I opened the hood and found the top radiator hose (between thermostat outlet and radiator) was hot and the coolant inside boiling. I felt the radiator cap, which was cool to the touch, and felt the lower hose (radiator to water pump) and it was cool. Overflow bottle level is still at the cool mark and isn't boiling. Fast forward a few hours later, I open the radiator cap and the coolant is full to the top like it was before. I started the engine with the cap off and after a few minutes the coolant started surging out of the radiator, and the gauge was back toward 2/3 (hot).
I'm guessing I have either an air pocket or the thermostat just up and died. I changed the thermostat and water pump not too long ago. Any thoughts or suggestions? If I run it with the cap off to burp it the coolant surges out then goes back down.
Thanks.
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