Looks like a bad water pump. Easy thing to change. I first changed to an AirTEx -- it leaked, even brand new. Switched to an AC Delco. Problem solved.

You should be able to catch most of the coolant; only has to drop to a level below the water pump. Might as well change out the thermostat and thermostat housing while you are at it. And the the stubby hose, and the crossover pipe with a new temp sensor. Then you will be sure and done with it.

 

The fact that the temp goes down with the heater on suggests that you have a problem with coolant circulation (water pump) or with the thermostat. In both cases, the heater helps as it provides additional coolant circulation by its electric pump and it also provides additional cooling by its radiator.

Your coolant leak appears to be from the water pump but the leak itself should not cause the problem that you are having (until the coolant level drops too much). It looks like you need to replace the water pump and I would also replace the thermostat, unless replaced recently.

 

If everything was fine with the car previously .... changing the coolant should not cause any issues. The procedure should be to fill with coolant and then run engine with cap off and ACC controls on high temp with the AC compressor off. You want the the coolant to circulate and any air to come out of the fill tank .. you don't want the ac compressor running and creating any more heat.

When the thermostat opens you may get a drop in coolant -- so top up. The final procedure is to fully fill the tank and put on the cap -- any excess coolant will flow to the overflow in the fender.

Something else is going on with your car .... If all was fine prior -- I'm afraid maybe now not.

The temp gauge is not linear -- and will stay in normal area for an extended temp range .... once it moves the engine is in danger.

 

Man I hate these radiators with no fill neck..I would suspect a gel condition in the radiator..but you cannot easily see inside of it...the coolant colors don't mean much anymore...you have to go by it being long life or not....and the formulation....a possibilty

 

Ditto this!

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