Water reserve for water pump keeps emptying out after I drive for a little while

The top of radiator may be leaking.

I would be thinking radiator or water pump. When the engine is warmed up and the upper hose is hot, feel the lower radiator hose. It should be hot too, just a little cooler than the upper hose. If there is some blockage in the radiator, the lower hose may feel cold or just lukewarm.
Even though the water pump doesn't leak, the impellers may be made of plastic and have considerable wear. That would restrict circulation.
The heater core should not be an issue. Heater cores do not cause overheating even when totally plugged up.

The thermostat may not fully open. When this happens the flow is restricted and the water will enter the overflow since there is no where else for it to go. Also you may want to check the water pump, they can slowly go bad and they show the exact symptoms you described when they do.

We need more information. I am thinking fuel filters and/or a weak fuel pump. Always consider the least expensive first. Some people drive on the last eighth of a tank of gas, and never put in more than a few dollars worth of gasoline. At night when it cools down the ambient air in the tank cools down and the moisture in the air condenses out to form water in the fuel. Water in the fuel will make any vehicle putter when driving. If such is a possibility then buy a couple of little bottles of fuel line antifreeze even in the summer and pour it in the fuel. The pure alcohol mixes with the water in the bottom of the tank and takes it through the motor and out the exhaust. The puttering stops if the problem was water in the fuel. In future fill the tank and drive on the top half of the tank. The fuel in a nearly empty tank in the summer gets so hot that it cannot cool down the fuel pump under normal use. In the hot summer it is paramount to drive on at least a half full tank. Cars driven on the last liter or gallon of gas burn out the fuel tank pumps in short order. Keep the fuel level over the half mark winter and summer. Save hundreds of dollars on replacement of fuel pumps.

First of all see the fan is working,this probably the main cause,secondly it can be the water pump not working.I give a tips,to know if the the pump is working properly,when the engine is cold,you take out the hose from the radiator,the upper one,when doing that your radiator must be full of water,now let someone start the engine and you stay in front of the bonnet ,when already start the engine ,see from the the hose that you have taken out if water is coming out well,accelerate a little more see if the water come out rapidly and constantly,be careful not to let the radiator empty keep it with water keep filling it by using a water hose,if the water pump is not pumping enough that the cause of over heating.

Inside the coolant reserve tank there is a sensor for coolant level.


Over time,this sensor can get stick.


Inspect the coolant reserve tank for crack or leak.

Locate the coolant level switch/sensor and soak it in clean warm water.

Make sure it's free to move up and down the float path.

Top off the coolant tank with coolant only.

Replace the thermostat, it will regulate the operation of the water pump and if the leakage is due a crack or from any part of the water line get it repaired..........sodeep

Water pump gone.

No this is not normal. Have you had a look at the water pump? It might pay to have the system pressure tested as there may be a leak that is happening while you are driving...

will pepper swtop a radiator leak
Improvement done by sickofjunk
There are radiator sealants available at many auto parts stores. I personally have never been able to get them to work though another good way to seal a leak if it is on the aluminum part of the radiator is to soder it with silver soder. And no i don't think pepper will stop a radiator leak.