Hi all, here is my problem : when the car run at idle the temperature go up and it gets very high and if I turn on the heater in the car the air coming is cold...so it looks like water don't flow at low rpm. When I raise the rpm a little (car still not moving) the heat goes down and the air from the heater become hot like it should.
My guess is that the water pump is not pumping anything at low rpm and need to be changed, but before ordering a new one I would like to know what you guys think...

Thanks

A water pump failure is a catastrophic event seeing as how its included in the timing belt loop. If the pump were to seize or otherwise stop pumping coolant, your car would have severe damage that you would recognize immediately. That's not to say that these things never happen, but you would know it if the pump failed.

Check and replace the thermostat to eliminate that as a potential cause.

You have air in the coolant system and you need to burp it. Top off coolant, warm the car up, turn it off, let it cool down, and repeat these steps. If after 4 tries it still loses coolant, swap the thermostat and radiator cap.

^^^^I'd go with swaping out the thermo and cap too.

Thanks all, i'll top the fluid and see if there is a leak.

do both the upper and lower hoses feel hot to the touch when the temps rise during idle?
if not your radiator failed / cloged

if they do then. . .
take off the cap and turn the car on as it warms up you should be able to see the thermostat open and coolent start to flow.
you will also be able to see any air bubbles coming out too.

Ok, First thing just like everyone else has said you must make sure water is actually moving, try loosening your hose and start the car, when it get ot operating temp it will start to leak fuid because its moving, if you can manage to get it to leak even when loosening the hose then the coolant isnt making it through the thermostat. Replace that if not. NOTE THIS!!!!!!!: 1) When you take the thermostat out, but the thermostat housing back withour the thermostat in it, DO NOT connect the upper hose at this time.
2) Start the car. If fluid runs out the top hose ( the coolant return) then your water pump is functioning, Thats a good test, if there no coolant flow your waterpump is gone or the coolant system has a massive clog, 90 percent chance of a busted water pump at this point).
3)Now that your now the pump works take this time to Flush the system as there can be all kinds of junk thats made it into the system that can result in a Thermostats early failure. After the Flush re- install a Thermostat with a new one and replace the cap. Having a clean coolant system really narrows down the things that can cause the issue. Flush the radiator and engine block ( not when hot to prevent cracking or warping head) until the water runs clean.
Now that you replace the thermostat and radiator cap, hose and everything should be working, if it still runs hot at this point you need a water pump installed.