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Brad, ASE Certified Technician
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Experience:  ASE Certified Master Technician
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I have a 2004 Monte Carlo SS. A few days ago it started to

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I have a 2004 Monte Carlo SS. A few days ago it started to run hot. I changed the thermostat, it seemed to run fine. Then it started to do it again, so i put on a new water pump. It was fine for a few days now its back running hot. Help!!
Hello and welcome to!

Under what conditions is it running hot? Does it only do it on the highway? Does it only do it in traffic? Sitting still?

How hot is it getting? Is it actually overheating?

Is there a Check Engine light or any other warning lights on?

What brand thermostat and water pump did you install? What kind of antifreeze?

Customer: replied 6 years ago.

I havent let it over heat. When i see the temp gage climbing i turn the car off . It gets a few lines above the red no lights come on. I dont know what brands the parts were. My boyfriend put them on. I just checked the oil . Its normal. It takes about 15 minutes of street or highway driving before the temp starts going up. My boyfriend said it did over heat on him. He really doesnt know to much about cars.


OK what kind of driving are you doing when it is getting hot? Driving at a steady speed... or sitting still (like at a red light)?
Customer: replied 6 years ago.
both i was driving home from work on the highway going 60 for 10 minutes notice the temp gage creeping up got off the highway drove about 5 minutes doing 25 hit 1 red light and it was going up
OK.. you may just have air pockets in the system as a result of replacing the thermostat. Have him make sure he followed the procedure HERE.

If the system has been properly bled and it continues to run hot, then you need to make sure the radiator fan is running. If the gauge is near the red and the fan is not on, see if the fan comes on when the A/C is turned on. If it still doesn't come on then it's possible the fan itself is bad. If it does, then it could be a computer or cooling temperature sensor problem.

When the car is hot (close to overheating) have him CAREFULLY feel both radiator hoses, and both heater hoses. They should be all close to the same temperature. If not, this indicates a restriction somewhere.

Also if the fan is on, the air it is pulling through the radiator should be HOT... not cool and not luke warm. If the radiator hoses are both hot and about the same temperature, but the air from the fan is cool or luke warm, this indicates that the radiator is likely bad (corrosion inside coats everything and prevents the heat from transferring from the liquid to the radiator properly). Also if the air starts off hot and then cools off very quickly (and the engine is still overheating or close to it) this also indicates a radiator problem.

Check the engine oil.. make sure it is brown or black, and has no signs of a white or cream color, as this indicates water (or coolant) in the oil.. which is usually the result of a blown head gasket. This can cause an overheat, and this can become the product of an overheat as well.

It is also possible for a head to leak in a way that exhaust gases enter the cooling system, but coolant doesn't enter the oil. When the engine is cold, make sure the radiator is completely full and that the radiator cap is installed. Start it up. It should take a minute or two for the upper radiator hose to become pressurized (stiff). If this happens immediately, this is usually a case of a head gasket problem. It is possible for this to happen, but not so rapidly -- but testing for it might require emissions analyzing equipment. Just because it passes the 'driveway' tests I just gave you, doesn't necessarily mean the head and head gaskets are good.

Also too little or too high a concentration of antifreeze can also cause overheating, especially on a very hot day. If using full strength antifreeze, you're supposed to mix it with water (50%/50%). If using the premixed stuff, then don't add any water.

He needs to start with bleeding the cooling system though. some of these motors have two bleeders, and some only have one.. Some use a standard head screwdriver, and some use a 7mm socket. When the engine is cold, make sure the cooling system is full and open these bleeders until only coolant comes out of them. Carefully close them (very easy to break so barely crank them tight) and follow the procedures listed in the link above.
Brad, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2366
Experience: ASE Certified Master Technician
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