How do you know if you need to replace the water pump or the radiator?

All of the answers thusfar are accurate. There has to be a leak for your coolant system to lose coolant/water. If you're refilling your radiator, you need to make sure to have the right mixture of coolant and water. It should be half and half. Check the hoses to make sure they were tightened up after the radiator was replaced. There is a small hole (weep hole) on the water pump that will show a coolant trail if it is leaking. If the radiator was only replaced two months ago, I'd ask the placed that did the replacement to check for leaks. There should be a warranty for the radiator or the work done. I'd start there since it hasn't been very long. The longer you wait to have them check it out, the more likely they won't be as helpful. You need to show the problem right after the work was done or they'll assume you simply had another problem start up later. A pressure test is the best method of locating one or more coolant leaks, but if it's a hose it should be readily visible.

I hope this helps.

Good chance you have a leaking head gasket. Try this, with the engine cold, remove the radiator cap, start the engine and let the car idle until it heats up. Look into the radiator, can you see large bubbles (like blowing slowly through a straw into a glass of water) or a "foamy" looking coolant in the radiator opening? You also need to see if there is oil in the radiator. Is the cooling system loosing coolant with no apparent external leaks? Does the car loose coolant , but never leave a puddle on the ground? A leaking head gasket is common on engine with aluminum heads and iron blocks, especially if the engine has been previously overheated. Some shops have a chemical test for combustion gasses in the radiator. It is also possible to use a system pressure test, where the entire system is pumped up to 15-20 PSI and then allowed to sit and see if the pressure drops. A quick drop in pressure indicates a leak. A pressure test can allow you to see where a leak originates, since the car is sitting and a leak will be very apparent.

Look for a leak, probably a small leak. That's the only way an otherwise normal cooling system can lose coolant. Look for leaks around the upper and lower radiator hoses, heater hoses and the drain valve at the bottom of the radiator on the side that faces the engine, or a loose or ill fitting radiator cap.

The cooling system is a sealed system, that is all the coolant you put in the system at the beginning of the year should still be there at the end of the year. It won't boil off because water under 15lbs pressure won't boil until 357F. Now, if you car overheats, yes, some of this water can boil off.

Have it pressure tested and repaired. Do not let that engine

overheat or even run hot for that matter.

It does a lot of damage..

Fix it ASAP ..

You're not blowing white smoke out the exhaust are you ?

Hope this helps...

water pumps usually leak from the weep hole under them and make a noise and radiators don,t make noises.

when checking for leaks be sure to check underside of water pump...there is a seep hole there that when pump fails water seeps out...also if you hold fan blades and shake them back and forth,not turn, if you feel looseness the pump may be broken

suggest to find the leak. Suggest that First step would be to check the ground where the car is parked and go from there