Overheating water in reservoir empties quickly changed thermostat 2 weeks ago overheating again

wild guess , clogged rad tubes.
wild guess 2, pump impeller , rusted to near nothing
lots more,,, why guess, get the car serviced.

I think the head gasket has blown again. If the head was not skimmed correctly or installed correctly it will blown the gasket again. The fact that the water is bubbling in the reservoir but the gauge staying in the middle means the water is not actually boiling but venting air/gas from the cylinders to the water reservoir. Check for a whitish grey substance in the inside of the oil filler cap indicating water getting into the engine oil. Also with start up - the engine will misfire badly but improve after a while. Take it back to the mechanic as he should guarantee his workmanship.

You may have a blown engine head gasket. Check your oil to see if it is milky because water is getting into the oil, and check the water to see if oil is getting into the coolant.
If you have either of these, you may need to have a new head gasket for the engine, and hopefully you do not have a cracked engine head.
This will require a fair bit of work to fix correctly. Your local garage or mechanic may be your next call.
There are some products you can use in the coolant for either of these, but it is only a temporary fix.

sounds like the radiator is blocked either coolant flow or ext air flow through the matrix the thermostat can get ruined when the system overheats so allways change the stat after a overheat problem GET THE RAD CHECKED FIRST if ok check the coolant pump

Sorry to say you probably have engine troubles.
A leaking head gasket will drink the coolant and cause the bubbles to form.
A mechanic can check for leaks by pressurizing the cooling system and also checking for exhaust gas in the radiator.

SOUND LIKE COOLANT FANS HAS A FAULTY THERMO SWITCH LOCATED AT THE BOTTOM OF THE RADIATOR ON LEFT HAND SIDE.CHECK THE FUSES 8 IN THE ENGINE COMPARTMENT AND CHECK FUSE 16 IN THE PASSENGER COMPARTMENT FUSE BOX.WHEN ENGINE OVERHEATING IF BOTH COOLING FANS WORKING.OVERHEATING PROBLEM COULD BE BLOWN HEAD GASKET.CHECK ENGINE OIL LOOKS LIKE MILK HEAD GASKET LEAKING.SEE WHEN YOU DRIVING LOW AND HIGH SPEEDS THE COOLING FANS SUPPOSE TO BE RUNNING.IF THEY NOT RUNNING THAT IS YOUR OVER HEATING PROBLEM.

Hi, check you have heat coming out the heater in the car put it on hottest setting and see what happens if it comes out cold then the chances are the head gasket has gone and is pushing gasses into the coolant system causing an air lock and then over heating.

check the oil for signs of a white substance look on the oil level stick and also inside the oil filler cap if their is any signs of milky substance then this is proof head gasket has gone.

let me know what you find out ok

It could be both your thermostat and water pump, it could also be an air lock in your cooling system. One way or another, I think pressure is building up in part of the system because its not circulating properly.

When its cool, take the top off your reservoir, give the bottom hose to your radiator a good few squeezes, see if the water goes down a little, if it does, you moved something on and probably cured it.

If not, run the engine up, to get it warm and bleed off any air in the system. (Assuming there are bleed taps in the system)

If that also does nothing, I reckon its your water pump. And if your changing that, I'd suggest changing the thermostat at the same time.

your car problem is overheating, some car model like yours is designed to shut-down engine when engine temp. rise so as to avoid frying the engine. your engine overheating problem is attributed by one of these factors:
1. check or refill radiator water if less
2.check radiator cooling fan operation-if damaged pls. change or check the electrical system.
3. damage/ worn water pump-if damage pls. change the water pump.
4. check for any coolant leak somewhere the coolant line-pls. rectify the leak.
5.worn coolant reservoir cap- change if damaged.
6. clogged radiator-if clogged pls. change it.
7. damaged thermostat valve.

I guess the burning question is , where is the coolant going.
Is this a 4.3 engine? How many miles does the vehicle have?
Has the intake gasket been changed?
I'm guessing a can of "Bars Leak" may cure your problem.
Let me know.
Regards,