How to diagnose a bad water pump

What's the actual temp of the engine ? Hooking up a scanner that can view engine sensor data ,would be one way to tell or using a infrared thermometer gun. You can buy one for less then $30 at harbor freight tools . Do the cooling fans turn on at 221 drgrees . Turn on the A/C ,do the cooling fans come on ? GM had bad step motors in the instrument cluster from 2003 to 2006 . These step motors control the gauge needle position . Replaced a bunch of these instrument clusters because customer thought the vehicle was over heating ,but wasn't . Having the correct tools an knowledge , could have had it diagnosed in just a couple of minutes .

Very possible that indeed the water pump is bad. These things do have a lifetime, and 15 years isn't all that short a time.

bad water pump

If you replace the water pump and thermostat and nothing is leaking, and still the coolant is low, then you vehicle is burning coolant, that give you a misfire and a flashing check engine light. so look like you need a head gasket job.

Sorry if I don't put things in a nice way.
If the thermostat is bad either the temperature is low, or is hot but no misfire (chatters)

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if temp. gauge goes up above normal you need to first check the coolant level in the overflow tank. if at normal spot ( car not using any of it). your themostat is bad.

Have you tested the thermostat yet? Are you "sure" it's working? That engine is NOT known for having water pump impellers going bad at all. I would believe a bad t-stat before a bad water pump. In my enperience if it's now flowing water, start there. If you can, take the t-stat out and put it in a pot of boiling water on the stove. Use a meat thermoneter, or even a cany thermometer and check the water temp. the T-stat should open up on it's own, even without water flow between 195 and 210 degrees. If it isn't, there's your problem. Start there, ESPECIALY if you "just put in a new T-stat." I've had FOUR bad t-stats brand new out of the box from 3 different suppliers in 15 days at my shop. I'm testing them before installing them now. the Stick

what a kind engine? diferent engine diferent cost

Yes, I am sorry to say this could be a blown head gasket. It could also be a bad water pump. Lets hope that it is the pump. You can get a pump replace for under $200.00 as opposed to the head gasket which runs over a thousand. It really sounds like water pump problem because you are not getting heated water to you heater core, where This would also cause the non mixing of fluids. Take the radiator cap off and see if you get bubbles rising to the to cover. Also if you rev the engine up and water comes shooting out the radiator cover hole the you definetely have a head gasket problem. Be very careful not to burn yourself. I bet anything it is just a pump. Gaskets ususally only go bad if you drive the car while overheating. Lets get this solved for you. Send me your qustions and we will get you taken care of. Please leave me good feedback, it means a lot to me....

Water pump. No question in my mind, water pump.