My 02 gran prix is getting hot i keep having to add water nd my heater doent blow warm air when doing this but then the temp gage will drop back down nd sometimes the heater will start to work rt

Your temp sensor has nothing to do with your heater. The temp sensor needs coolant in order to work properly. So first check the coolant level because if it is low your heater will act the way you describe. Once the coolant gets low enough the heater will blow cold. Another possibility is the radiator cap. After the engine has warmed up it expands when it cools down it contracts. As it is contracting if the cap is weak air can be drawn into the system and cause air pockets to form and will cause the same problem

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

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Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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No heat on car? http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows intermittently and temp gauge goes erratic? http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html------------Heater blows cold? http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html
---------Car heater blowing warm, but not hot air? http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html-------- Heater/AC blower motor not working?

http://technoanswers.blogspot.in/2012/02/heaterac-blower-motor-not-working-on.html

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A/C, heater, defroster fan, not working? http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html Heater problem? http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html---------

This will help.Thanks.

You've got air trapped in the cooling system.The lowering and rising is caused by the water pump sucking the coolant into the engine thru the bottom radiator hose when the thermostat is closed. When you let off the throttle, the water pump slows down, an since the thermostat is closed, the coolant has nowhere to go except back into the radiator.You need to bleed the air from the cooling system or it can cause over heating and the heater may not work right. Here's how to go about it: You'lll need a gallon of antifreeze. Use a jack to raise the front of the vehicle so the radiator is higher than the engine. Remove the radiator cap and start the engine. Make sure the heater controls are on the hottest setting, but do not turn the heater on. Let the engine warm up to normal temperature. Watch the coolant level in the radiator. When the thermostat opens, the coolant level will drop. Now, add antifreeze to fill it back up. If there is still air in the system, the level will drop again. Add more antifreeze. Continue to do this until the coolant level stabilizes. Put the radiator cap back on and make sure the temperature Gage doesn't show overheating. Turn on the heater to make sure it blows hot air. Your done

The next possibility, if you haven't already thiught of it, is as simple as making sure there is enough water/antifreeze solution in your radiator. If the level is too low, your hoses will get hot, but there will not be enought water to circulate into your heater core.

once the truck is fully warmed up, feel the 2 heater hoses going through the firewall in the engine compartment. they should be hot to the touch. if they are, then the problem is most likely the heater controls, such as the temp. switch on the dash or the blend door itself inside the dash. if they are cool, check that the coolant is completely full. just because the temp gauge reads normal doesn't mean there's enough coolant in the system to fill the heater core. remove the radiator cap once cooled and top off if needed. if it is, or was, low, its possible to get air the the cooling system and block flow of coolant to heater core.

dear friend-there is a couple of things you can do to find the problem,when the engine is cold remove the radiator cap start the engine then look inside to see if the water is circulating,all so look for bubbles in the water,if there is bubbles,you might have a blown head gasket,if there is circulation the water pump is ok,then get the engine up to working temp,then feel both the top and bottom radiator they should be the same temp,if not then the termostat is at fault

You may have an air pocket in your system which some times happens.  One way to get rid of it is to take the upper hose off on the engine side,  fill your system with water until it runs out from your engine block, replace the hose, start your car turn you heater on and set to hi keep the radiator cap loose until the temp start to rise then close tight.  Once the air pocket had been remover you can drain some of the water from the radiator using the lower drain plug and add antifreeze.   

There is a flat filter that sits between the firewall and the blower. Sometimes the filter is blocked and needs to be cleaned or changed. On older cars the filter is located on the firewall in the engine compartment infront of the blower. In the newer cars the filter is under the dash inside the car and much harder to get too.,

Just finished fixing my daughters 1999 taurus heat. It would blow warm only when running down the road. At idle it blew cold. I started with replacing thermostat, and water pump because they are the easier fix. Still did not help. Then I replaced the heater core. A daunting job but not that hard to move the dash slighly out of the way to replace. There is a good write up at tarusclub.com. After that, heat was better but at idle, it would still blow cool sometimes. Researched and found answer. Park car on the steepest hill you can find with front of car up. Start car and take off reservoir cap. Let car warm up and keep rpms about 1500. After a while the fluid will come running out of the car and all over the place but it will bring air bubbles with it. Reduce rpm, add more fluid and repeat about 3 times. It will make a mess but after that, the heater works perfectly. We get heat long before the temp gage indicates any and it never blows cold unless you lower the temp.

I would suggest replacing the blower motor resistor. When this component fails the blower will only work on one spped or none. This is a very common issue with all automotive models