Chasing a cooling system issue

[GA_PI]

A few months ago, my 98 Civic DX blew the large upper hose so I replaced the upper and lower hose plus the thermostat. After I changed the hoses, the dash gauge started bouncing all over the place. So I started chasing this. Changing a sensor in the radiator caused a leak so I replaced the radiator plus all other sensors, the relay and fuse. One of the heater core hoses blew so that was replaced. Discovered the water pump and time belt were original with 150k plus miles so replaced those. On the off change the fan was bad, that has been replaced and I have replaced the coolant reservoir when I discovered a hole in the cap. I have bled air out of the system and check the antifreeze temp while the engine was hot. The temp never rose above 180 even when the gauge was in the red. The car has been checked for head gasket leaks and passed with flying colors. I am down to a temp gauge that still bounces around and a reservoir that will fill to overflowing. Some times the fluid is drawn back into the radiator other times the fluid remains in the reservoir. Suggestions?

 

[XpL0d3r]

Test the thermostat - it might be stuck. It's not all that uncommon to get a bad one right out of the box.

Drop it into a pot of hot water and it should open up. Take it out and it should close once it cools down. If it doesn't change, or changes and then doesn't change back, replace it.

 

[mc360]

If the overflow isn't getting sucked back in then it's most likely a blown head gasket, with all the blown up hoses I suspect that your only pressurized the cooling system with combustion gases rather than mixing oil and coolant.

Get one of those radiator testers that test for combustion gases in the coolant