Cooling system problem

My 99 Cavalier is overheating. I've already replaced the thermostat, removed and flushed out the metal heating system tube(s), flushed out the heater core in both directions, replaced the water pump and put 2 gallons of 50/50 antifreeze back in. Capacity is 10.3 qts.

Yesterday after replacing the water pump, I started it, let it warm up, took it for a ride and it was fine for several miles until I got on it a little. Soon after I lost heat and the temp gauge started to rise. I let it sit overnight. This morning I put more antifreeze in (this brought the total to 2 gallons). Started it...had good heat....drove it several miles all normal....got on it a little...started loosing heat soon after and temp gauge starts to rise.

Underneath nothing is dripping. No cloud of steam or anything abnormal coming from the tail pipe. No signs of coolant on the dipstick.

It appears to be losing coolant to the point where there's nothing in the pump to circulate...the heater coil is on a bypass so if there was any coolant there to pump we'd have heat. During the last test drive the coolant tank went down about an inch from the "full cold line".

I'm stumped. Anyone have an idea?

 

The coolant could be going out the overflow on your reservoir tank. What could be happing is you have a small leak with a head gasket and when getting on it the leak pushes out the coolant to the tank. Fill the system up again and do not fill the reservoir tank then you need something to check to see if coolant is going out the overflow tube. If you can setup some kind of empty food can to catch some coolant if this is where it is going. Do you test drive once again but first let the engine get to operating temperature first setting in place. This will let the thermostat open so as not to get a pressure build up before the test drive. Now this is very tricky, after the engine is warmed up remove the cap on the coolant system, but remember that the system has pressure and have your hand covered with a multi layered thick cloth and just twist the cap to the safety catch to let off pressure. When the pressure has been released then and only then remove the cap. This is done with the engine running and let it continue to run for 5 minutes and at the end of the 5 minutes check for air bubbles do to a leaking head gasket. If all is good and no bubbles reinstall the cap and do a test drive and get on it, if coolant is escaping out the overflow it sound like the radiator is plugged. Great care needs to be taken when removing the system/radiator cap with the engine warmed up. If you do not feel competent to do this step skip it and take the care to a shop to check it out. If not done correctly you could get bad burns from the coolant rushing out of the system. Coolant will rush out.

 

Dear RRR....

You nailed it. Thank you for a thoughtful response. I think my problem all along was a loose reservoir tank cap. I had it off a couple of weeks ago and may not have put it back correctly. I discovered this after my post this morning. I brought the coolant level back to where it should be and made sure the cap was right. Drove 10 miles...got on it many times. Everything is right. I now think a little coolant was escaping each time it was driven and finally got low enough to stop pumping. I now believe if I had refilled the system at the first sign of trouble the other many hours of work would have been unnecessary.