Radiator reservoir overflows

no
as the coolant heats it expands and the radiator cap lets off into the reservoir that fills the reservoir
as the coolant cools down the radiator cap allows the low pressure in the cooling system to draw coolant back from the reservoir
To need to add coolant indicates that the draw back process is not happening possibly from the overflow hose not sealing off properly and allowing air back in and not drawing from the reservoir
check the reservoir for cracks as well

Remove radiator cap when car is completely cold. Refill radiator look to see circulation when cap starts turn heater high. When thermostat opens water will be drawn from overflow into radiator. If this does not occur faulty thermostat is probable cause if no circulation change water pump. Refill water to correct levels and car should run correctly

Are the cooling fans coming on?

The overflow tank won't cause it to overheat. If you have added radiator stop leak just replace the radiator is stopped up.

you may need to replace the thermostat or the water pump to solve the overheating issue.
The leak in the overflow was NOT the cause of over heating.
You do have a radiator cap. It is the one on top of the overflow.

The radiator drain petcock is on the bottom of the radiator near one of the corner edges.
(Some face engine, others face the grille)
If for some reason you still can not find it, you can always pull the lower radiator hose (make sure water/engine is cold)

once you flush/fill the system, use a 50/50 mix of water and the proper antifreeze. (older cars use green, newer use orange)

If you are unsure, just ask the guys at the auto parts place which one you need and note that they sell an orange color that can be safely used in old and new cars and it can also be mixed with any color of fluid.

After you have the system filled, start the engine and remove the fill cap.... let it run and watch for air to rise out from the opening. (Some coolant/water may overflow, but you need to watch for any air bubbles coming out)

Once you don't see any air trying to escape, put the cap on tight and you should be good to go,

Another cause for overheating is air trapped in the system.

I hope this helps.

DID YOU BLEED AIR OUT THE COOLANT SYSTEM.TO BLEED COOLANT SYSTEM, FILL THE COOLANT SYSTEM THROUGH THE RESERVOIR TANK OR THE RADIATOR UNTIL THE FULL COLD MARK IS REACHED.BESURE TO USE 50/50 HALF WATER AND ANTIFREEZE.YOU CAN BUY ANTIFREEZE THAT IS ALREADY PREMIX 50/50.AFTER ADDING ANTIFREEZE TO RESERVOIR OR RADIATOR FILL RADIATOR TO FULL MARK OR IF YOU DONT HAVE RADIATOR CAP ON RADIATOR POUR ANTIFREEZE IN THE OVERFLOW JUG UNTIL COOLANT LEVEL STAY THE FULL COLD MARK.WAIT AWHILE UNTIL COOLANT LEVEL STOP DROPPING.NOW INSTALL THE RADIATOR OR OVER FLOW JUG CAP.START THE ENGINE AND ALLOW IT TO RUN UNTIL NORMAL OPERATING TEMPERATURE IS REACHED AND THE UPPER RADIATOR HOSE BECOME HOT.STOP THE ENGINE AND OBSERVE THE COOLANT LEVEL IN THE OVERFLOW JUG. THE COOLANT LEVEL SHOULD BE AT THE FULL HOT LINE.ALLOW THE ENGINE TO COOL UNTIL THE AMBIENT TEMPERATURE IS REACHED THEN CHECK THE COOLANT LEVEL IT SHOULD BE AT OR ABOVE THE FULL COLD LINE.ADD MORE COOLANT IF NECESSARY. WARNING BECAREFUL WHEN OPEN THE RADIATOR CAP OR JUG OVER FLOW CAP.USE A LARGE RAG OVER THE RADIATOR CAP TO KEEP FROM GETTING SCALDED.OPEN RADIATOR CAP A LITTLE AT A TIME TO KEEP FROM GETTING SCALDED.WAIT UNTIL ENGINE COOL DOWN BEFORE OPENING RADIATOR CAP OR OVERFLOW JUG CAP.WEAR SAFETY GLASSES.

when vehicle gets hot and has too much fluid it dumps what itdoesnt need then later as it cools it sucks back what it needs sounds like the level of fluid in reservoir is too full only fill to line on jug....also inspect overflow hose...unless it is overheatingthe rad cap is pressure sensitive....if this is problem thermostat stuck closed replace thermostat.

It is normal for some antifreeze move into the overflow tank when the engine cools down after it is shutoff and draw the antifreeze back into the engine when it is warmup, but if it is push antifreeze into the overflow tank and overflowing the tank then most likely the cylinder head is cracked or the headgasket is blown. You can take it to a automotive shop and have them check for hydrocarbons (exhaust gases) in the radiator.

Good luck

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.

yes, not having an overflow reservoir for your radiator will cause you to lose water. As your engine warms up the water expands and creates pressure in the cooling system. When the pressure reaches a certain point(usually about 15 psi.) the radiator releives the pressure by releasing water into the overflow tank. When the engine cools back down the water shrinks pulling water back into the radiator from the overflow. If there is no overflow, the everytime the engine warms up on a drive water will be lost and not recovered on cooldown.