Car overheats. i unplugged temp sensor and fans suddenly came on and coolant started to flow. hoses werent backed up any longer. so i replaced fan relays and car is still running hot

If the cooling fans are not coming on when the vehicle is overheating try this.

Look for the coolant temp switch B. it will be located near the thermostat housing on the back side of the passenger side of the engine (follow the lower hose to the engine). It will have a white with green wire and a black wire. Unplug it, turn the key to the run position, the engine does not need to be running. ground the white with green wire. if the fans come on replace the coolant temp switch B sensor.

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i would check and make sure the cooling fan is operating,if not it will overheat sitting still.a thermostat will cause overheating whether or not it sits still or driving(more so when driving).the same if it has a bad water pump although it may circulate just enough coolant when driving to not overheat with air flow also adding a cooling effect.if you don`t have a leak then i would say the water pump is okay as they usually will leak before causing a overheat problem.make sure the cooling fan is working and the rad does not have anything stopping the air flow over the rad and is not stopping coolant flow in the rad.

You will need to see if the fan operates when overheating, there are diffrent sensors for the cooling and ac cooling, the good thing is that the fan works, this would tell me it may be a bad coolant temp sensor or thermostat, you will need to let it run and as the gauge passes the middle point feel to see if both upper and lower rad hoses are hot, if only one is hot then you may have a bad thermostat, is they are both hot and fan doesnt turn on and car overheats then you should replace the coolant temp sensor, stat with these tests and see the result, hope this helps.

For first check the coolant level.If its low then it must be made full.If its full then check out for any kind of coolant leak.If the coolant is low or getting leaked from somewhere then the car will overheat.So get the ac pressure test done.At any local car garage they do ac pressure test.Doing this test will let you know that there is coolant leak or not.If there is coolant leak then that leak is the cause of overheat.But if there is no coolant leak and coolant level is also full.Then ignore coolant cause for overheat.Then other cause may be the thermostat ,thermostat allows coolant to circulate when the engine is warmed up and should be closed when the engine is cold so that the car can warm up faster. It's a fairly inexpensive part that's replaced easily, but when it fails, your car can overheat, causing costly engine damage.
To check if thermostat is faulty try this procedure:-- Warm up the car but don't let it overheat--don't let the thermostat gauge go into the red.Turn off the engine.Open the hood.Find the upper radiator hose. It's black, is made of rubber and is about 2 inches in diameter, with metal clamps on either end. The upper hose goes into the top of the radiator.Locate the lower radiator hose. It looks similar to the upper hose except that it attaches to the bottom part of the radiator.Touch each hose very carefully (they can be extremely hot). If the temperature gauge is indicating that the engine is warmed up but one hose is hot and the other is cold, the thermostat is probably stuck closed, and the coolant isn't circulating through the radiator.the thermostat is faulty is the case. If the thermostat checks out ok then it can be faulty temp sensor.Its also called coolant temperature sensor. The coolant temperature sensor is a thermistor ( a resistor which varies the value of its voltage output in accordance with temperature changes. ). The change in the resistance values will directly affect the voltage signal from the water thermosensor. As the sensor temperature decreases, the resistance values will increase. As the sensor temperature increases, the resistance values will decrease.
The coolant temperature sensor lets the engine control computer know what the engine temperature is by gathering information from the engine coolant temperature. There are several ways to know if the coolant temperature sensor is malfunctioning, if the sensor is bad it will trigger a trouble code and the check engine light in the dashboard will come on, you can retrieve the engine code and see if it is related to the coolant temperature sensor, even if the engine control computer doesn't store a trouble code, there is another way to suspect a bad coolant temperature sensor : If your vehicle starts using more fuel than usual, starts having trouble starting when the engine reaches normal operating temperature or you notice black smoke coming out from the exhaust tail pipe, it is very likely that these symptoms are related to a bad coolant temperature sensor. A thermostat that is stuck closed will cause the engine to overheat. To test if thermostat is stuck in the closed position, place the thermostat in boiling water. If the thermostat doesn’t open, than the thermostat is defective and needs to be replaced.
Check the Engine Coolant Fan
Since the cooling fan pushes air through the radiator to cool the coolant, a fan that’s not working properly will cause an overheat condition.

1. Electric Fan – If the vehicle is equipped with an electric cooling fan, check to see if the fan is working properly. Most electric fans will only operate when the coolant temperature reaches a certain degree. In many vehicles when the air conditioner is turned on, the electric fan automatically turns on. The most common cause of an electric fan failure is the fan motor, a controller module or a relay.
2. Engine Driven Fans – Some vehicle have cooling fan driven off the front of the engine. If the clutch (between the fan and the engine) is bad it may slip. If the clutch slips it may not allow enough rotation on the fan to be affective and the clutch needs to be replaced.

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Hello Guest and thank you for asking your question, on Fixya.

Here is a simple process that will walk you through a few steps that will pinpoint the overheating problem on your 2005 Chevrolet Monte Carlo, without even using any tools. It has helped millions of people, and I am certain that it will help you, because I wrote it for people like you. So here is the link to:
How to diagnose your overheating 2005 Chevrolet Monte Carlo

Anyways if that helps you any little bit, then feel free to follow me on Twitter. That one is at: twitter.com/acoates23234

Thanks for the vote, and good luck!

check to make sure the lower rad hose isn't collapsing when engine is reved

okay, if it turns on with coolant temp sensor unplugged, then this tells me that the fan is good and also relay is good, you replace thermostant, and the sensor, you covered all those bases,now we go into coolant flowing,this tells me the coolant is not flowing inside the motor,two thing can cause this, one being the waterpump, the impeller may have broken or rusted, and the next would be exhaust entering the cooling system restricting the flow and making it overheat,this is gasket from a headgasket problem. the next thing i would do is to have a block test done to see if exhaust is entering the cooling system, good luck.

NO, the sensor is good.

The coolant temp sensor tells the computer tempurature of engine at all times.It tells the coolant fans to come on,and also very important,when to cut off.If the fans don`t go off by them selfs,then temp is not going down.Now this is if the ac is off,cooling fans come on any time ac is turned on,so check for fans coming on and off with ac off.A bad coolant sensor would cause the fans not ot come on,but not to cut off nessasaralyCoolant systems must be bled of air trapped in systemfor the engine to be cooled .If air is in the system,the coolant won`t flow correctly.