how can I tell if it is water pump bad or thermostate bad

You don't say anything about make and mode which is always important. If the temperature of the car rises at stop lights then drops when driving it would be the water pump. The thermostat would not cause a leak of coolant and they rarely go wrong they are very simple devices with little to go wrong. The average lifespan for a thermostat is far longer than three years they can last twenty years easily.

losing coolant ,its the pump, the stat is good enough if heat came on when you took off, the rev,s moved some hot water to the heater, but was low again to not be going around all the time, so just keep the rad topped off till you can fix the pump. and those prices sound high for either job, maybe im out of touch, ??

I too feel that the prices seem high for the repairs if they were to be on a typical car , if it were to be on something like a Mercedes 104 Twin cam engine where the bolts are almost impossible to reach it would be a fair price. Without knowing the make and model it is hard to know if it is a fair set of prices. However the thermostat replacement is a 15 minute job on virtually any car. The retail price for a thermostat is only about 20 bucks so it's not too hard to figure whether your paying too much for that one.

Sounds like a water pump issue. Have you run the engine and looked under for coolant traces? i suggest this just to rule out hose or joint or tank leaks. What is the vehicle mileage? I know you are trying to economize, but if the mileage is above 90K, the timing chain should be replaced, and to access water pump substantial disassembly is required, exposing timing chain.This would save you in the long run, not to mention preventing a potentially severe engine malfunction/inconvenience. This engine, is designed to exceed 200K with regular service, especially with recommended oil changes since the early 2.7 can sludge. I suggest synthetic if you can afford it as an extra precaution, it lasts longer and protects in hot, and starts easier in cold weather. Good luck to you.

My 2004 Sebring GTC is in the shop right now for the same issue. It was low on coolant and it overheated on me. I stopped on the side of the road and had someone bring me some antifreeze. I added some and it ran well enough to get home. I have had a squeal coming from the engine compartment for a while now and I had the belts replaced. This did not fix the issue so I took it back. They changed the water pump today and said that it still has the squeal. Not sure what it causing the problem yet. They told me they were going to replace another part in the morning. I do not know what part they are referring to, just that they are going to replace it. I should have the car back tomorrow with hopefully no issues. It sounds like a common problem but if they replace the water pump and it is still making the noise then what is it? Plus, now I feel I replaced the water pump for no reason. The shop is charging 800+ to change the water pump. Apparently it is a lot to take appart to get to it and the timing chain can be inspected and replaced if needed at this point. Lucky my timing chain was good. Anyone else know what else can cause the problem? I never noticed antifreeze on the ground but I am worried it is leaking into the motor somewhere. Like a head gasket or something? Thanks for any advice.

I think if you are missing coolant and blowing cold air pherhaps heater core check floor boards for dampness and see if your windshield fogsup that's another sign however worst case scenario you may have blown headgasket. I have had these problems before.

I have a 99 ford mustang I changed out the hoses and everything but for some reason the reservoir had no coolant and I had to keep putting water ....there is a light smoke when driving it and I see my coolant leaking under the car but my radiator is full can it be water pump and how much do you think it will run me