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Sion · 01-11-2004, 12:47 PM

thermoSTAT, not thermometer, GS.

volman, first off, make sure the radiator and the overflow bottle are properly filled with coolant. an underfilled heating/cooling system often will not produce heat in the passenger compartment. if you find that it is low, start looking for leaks. this is a closed system that should NOT use up coolant. therefore if you are low on the fluid, then there is a leak somewhere. get that fixed.

ok, now let me give you a quick rundown on how a vehicle's heating system works. this is a generic discussion, so there's nothing specific to your car. however, the concepts are the same for about 99.999% of all cars, so you should be able to diagnose it with this information.

ok, it works like this. one of the by-products of the internal combustion engine is heat. and since too much heat is a BAD thing for an engine, there is a cooling system which is designed to keep it from getting too hot. this is accomplished by the use of a liquid cooling system, a radiator, a thermostat, a fan, a water pump and some hoses.

at cold startup, the thermostat is in the closed position, which prevents the liquid coolant from flowing through the engine. when the engine reaches a certain temperature (typically 195 degrees F), the thermostat (a spring loaded valve) opens to allow the flow of coolant. the coolant is forced through the engine and the rest of the cooling system via a belt driven water pump.

while in the engine, the coolant liquid absorbs heat from the motor and then carries it, via the uppper radiator hose, to the radiator. as it passes through the maze of radiator fins, the air that passes through the radiator removes the heat from the coolant. this process is assisted by means of a fan behind the radiator that pulls air through it. on older cars, this fan was belt driven, but on most newer cars, it is an electric fan that is controlled by means of a temp sensor (placed either in the engine (usually somewhere on the intake manifold) or else in the coolant system somewhere).

once the heat is removed, the coolant returns to the engine via the lower radiator hose, to begin the cycle again. so, once the engine reaches proper operating temperature, coolant is constantly cycling around and through the entire system keeping things at a constant temp of around 220 degrees F.

now, the passenger compartment heating system functions in the same manner as the cooling system. hot coolant flows (again, being pushed by the water pump) via small hoses called heater hoses, into a small radiator called the heater core, which is usually located under the dash. the flow of air though the heater core (as generated by the heater fan) picks up heat from the core and carries it into the cabin of the vehicle.

depending on the vehicle design, the flow of coolant into and through the heater core may occur even before the thermostat opens. if the vehicle has a by-pass hose, then coolant will be flowing through the heater system from the moment the vehicle is started. if not, then the thermostat has to open before this will happen.

now, in order to diagnose the problem, you will need to determine first of all if the thermostat is working properly. this is most easily accomplished by removing the radiator cap when the engine is cold and BEFORE you start the vehicle. (safety note: NEVER attempt to remove a radiator cap when the engine is hot, especially if the vehicle is over-heating, as hot coolant can spew out of the radiator and burn the shit out of you.)

first, make sure the radiator and its overflow bottle are properly filled (but NOT overfilled - see your owners manual or a Haynes/Chilton repair manual for details). ok, so you start the engine and let it idle while watching the fluid in the open radiator. after about 5 mins of idling, the engine should reach a temp high enough to cause the thermostat to open. at this point, you should notice the coolant in the radiator start to move, as it begins to flow through the system. if the coolant doesnt start to flow after 10 mins of the engine running, then the thermostat is stuck in the closed position and should be replaced. (warning: dont let the engine run much past 10 minutes if the coolant isnt flowing. it will overheat and severe engine damage can occur.) on the other hand, if the coolant is flowing immediately upon starting the engine, the thermostat is stuck in the open position and should be replaced.

NOTE: if your car is of the type that does not have a radiator cap, but only a cap on the overflow bottle, you may not be able to observe the flow of coolant in the manner described above. however, by feeling the upper radiator hose, you should be able to feel the flow of coolant once it starts. but be careful, the hose will get hot very quickly, so wear a glove while squeezing the hose slightly to feel for coolant flow.

NOTE: another cause of no coolant flow would be a water pump that has failed. in this case, the engine will overheat rapidly. as noted above, dont let it run too long, or you will damage the engine. if you replace the thermostat and still get no coolant flow, then one of three things has happened: either a) the T-stat is bad. you can test it before installing it by dropping it into a pan of boiling water. if it is functioning properly, you will see the spring expand and open the valve; or b) you put the t-stat in backward (the spring should face into the engine or in the direction of where the coolant comes from the engine); or c) the water pump has failed. if you got the T-stat in right, and still get no coolant flow, replace the water pump.

NOTE: if you car has a temperature guage on the dash, you may be able to diagnose the function of the thermostat by watching the guage (assuming it is working correctly). after starting the engine, the guage should climb rapidly during the first 5 mins or so. then it should level off at around 220 degrees F. (or in the middle of the guage if it is not marked with numbers). if the thermostat is stuck in the closed position, the temp will continue to climb and the vehicle will overheat, so dont let it get too high - shut it off if you think thats whats happening. if the thermostat is stuck in the open position, then the temp will climb very slowly and the guage wont quite reach the proper position/temp, instead likely hovering at or just below 195 degrees. in any case, its best not to rely to much on the guage, because it and/or the temp sensor that it relies on can be malfunctioning. so its best to use the above methods to verify actual physical flow of coolant.

ok, so if you've performed the above tests and everything seems to be in order with regard to the thermostat and the flow of coolant, then you need to examine the part of the system that flows coolant into the heater core. locate the heater hoses: they are about 1/2 to 3/4 of an inch in diameter and run from the back side of the engine (usually the intake manifold) over to the firewall. on most vehicles, the inlet/outlet tubes of the heater core stick through the firewall into the engine bay. on some, however, they may not. once you locate the heater hoses, start the vehicle and let it warm up (if it isnt already warm from the previous tests) and feel the heater hoses for heat and/or flow. one of them (the inlet that carries hot coolant into the heater core) should be hotter than the other, but both should be warm (again, be careful not to burn yourself). if the inlet hose is hot and the outlet hose is cold, that suggests a blockage somewhere, either in the hoses or in the heater core itself (most likely). (NOTE: the inlet hose is usually the larger of the two.) if neither hose gets hot/warm and you can feel no flow through them, that suggests a blockage at the engine.

so, once you have determined the cause of the heating failure, you can proceed to correct it, either by taking it to a mechanic, or if you have confidence in your mechanical abilities, by doing it yourself. if you decide to do it yourself, go get a Haynes or Chilton repair manual and read it carefully BEFORE you pick up a wrench. be sure you understand it fully before attempting anything. it'll cost you a lot more if a mechanic has to fix your fuckup in addition to repairing the initial problem. (no offense intended by this, just a friendly warning.)

ok, I think I covered everything. good luck and let us know how it turns out.

final note: with regard to coolant. DO NOT just pour raw coolant (also called antifreeze) straight into the radiator/overflow bottle if you find it low. this stuff is DESIGNED to be mixed with water, at a 50/50 ratio (for most climates, including Tennessee). too high a concentration of coolant CAN cause problems, including engine freeze-up in the dead of winter and/or excess corrosion of the radiator/heater core. ALWAYS mix before you pour it into the system.

01-11-2004, 12:47 PM	#4 (permalink)
Sion Dumb all over...a little ugly on the side Location: In the room where the giant fire puffer works, and the torture never stops.	thermoSTAT, not thermometer, GS. volman, first off, make sure the radiator and the overflow bottle are properly filled with coolant. an underfilled heating/cooling system often will not produce heat in the passenger compartment. if you find that it is low, start looking for leaks. this is a closed system that should NOT use up coolant. therefore if you are low on the fluid, then there is a leak somewhere. get that fixed. ok, now let me give you a quick rundown on how a vehicle's heating system works. this is a generic discussion, so there's nothing specific to your car. however, the concepts are the same for about 99.999% of all cars, so you should be able to diagnose it with this information. ok, it works like this. one of the by-products of the internal combustion engine is heat. and since too much heat is a BAD thing for an engine, there is a cooling system which is designed to keep it from getting too hot. this is accomplished by the use of a liquid cooling system, a radiator, a thermostat, a fan, a water pump and some hoses. at cold startup, the thermostat is in the closed position, which prevents the liquid coolant from flowing through the engine. when the engine reaches a certain temperature (typically 195 degrees F), the thermostat (a spring loaded valve) opens to allow the flow of coolant. the coolant is forced through the engine and the rest of the cooling system via a belt driven water pump. while in the engine, the coolant liquid absorbs heat from the motor and then carries it, via the uppper radiator hose, to the radiator. as it passes through the maze of radiator fins, the air that passes through the radiator removes the heat from the coolant. this process is assisted by means of a fan behind the radiator that pulls air through it. on older cars, this fan was belt driven, but on most newer cars, it is an electric fan that is controlled by means of a temp sensor (placed either in the engine (usually somewhere on the intake manifold) or else in the coolant system somewhere). once the heat is removed, the coolant returns to the engine via the lower radiator hose, to begin the cycle again. so, once the engine reaches proper operating temperature, coolant is constantly cycling around and through the entire system keeping things at a constant temp of around 220 degrees F. now, the passenger compartment heating system functions in the same manner as the cooling system. hot coolant flows (again, being pushed by the water pump) via small hoses called heater hoses, into a small radiator called the heater core, which is usually located under the dash. the flow of air though the heater core (as generated by the heater fan) picks up heat from the core and carries it into the cabin of the vehicle. depending on the vehicle design, the flow of coolant into and through the heater core may occur even before the thermostat opens. if the vehicle has a by-pass hose, then coolant will be flowing through the heater system from the moment the vehicle is started. if not, then the thermostat has to open before this will happen. now, in order to diagnose the problem, you will need to determine first of all if the thermostat is working properly. this is most easily accomplished by removing the radiator cap when the engine is cold and BEFORE you start the vehicle. (safety note: NEVER attempt to remove a radiator cap when the engine is hot, especially if the vehicle is over-heating, as hot coolant can spew out of the radiator and burn the shit out of you.) first, make sure the radiator and its overflow bottle are properly filled (but NOT overfilled - see your owners manual or a Haynes/Chilton repair manual for details). ok, so you start the engine and let it idle while watching the fluid in the open radiator. after about 5 mins of idling, the engine should reach a temp high enough to cause the thermostat to open. at this point, you should notice the coolant in the radiator start to move, as it begins to flow through the system. if the coolant doesnt start to flow after 10 mins of the engine running, then the thermostat is stuck in the closed position and should be replaced. (warning: dont let the engine run much past 10 minutes if the coolant isnt flowing. it will overheat and severe engine damage can occur.) on the other hand, if the coolant is flowing immediately upon starting the engine, the thermostat is stuck in the open position and should be replaced. NOTE: if your car is of the type that does not have a radiator cap, but only a cap on the overflow bottle, you may not be able to observe the flow of coolant in the manner described above. however, by feeling the upper radiator hose, you should be able to feel the flow of coolant once it starts. but be careful, the hose will get hot very quickly, so wear a glove while squeezing the hose slightly to feel for coolant flow. NOTE: another cause of no coolant flow would be a water pump that has failed. in this case, the engine will overheat rapidly. as noted above, dont let it run too long, or you will damage the engine. if you replace the thermostat and still get no coolant flow, then one of three things has happened: either a) the T-stat is bad. you can test it before installing it by dropping it into a pan of boiling water. if it is functioning properly, you will see the spring expand and open the valve; or b) you put the t-stat in backward (the spring should face into the engine or in the direction of where the coolant comes from the engine); or c) the water pump has failed. if you got the T-stat in right, and still get no coolant flow, replace the water pump. NOTE: if you car has a temperature guage on the dash, you may be able to diagnose the function of the thermostat by watching the guage (assuming it is working correctly). after starting the engine, the guage should climb rapidly during the first 5 mins or so. then it should level off at around 220 degrees F. (or in the middle of the guage if it is not marked with numbers). if the thermostat is stuck in the closed position, the temp will continue to climb and the vehicle will overheat, so dont let it get too high - shut it off if you think thats whats happening. if the thermostat is stuck in the open position, then the temp will climb very slowly and the guage wont quite reach the proper position/temp, instead likely hovering at or just below 195 degrees. in any case, its best not to rely to much on the guage, because it and/or the temp sensor that it relies on can be malfunctioning. so its best to use the above methods to verify actual physical flow of coolant. ok, so if you've performed the above tests and everything seems to be in order with regard to the thermostat and the flow of coolant, then you need to examine the part of the system that flows coolant into the heater core. locate the heater hoses: they are about 1/2 to 3/4 of an inch in diameter and run from the back side of the engine (usually the intake manifold) over to the firewall. on most vehicles, the inlet/outlet tubes of the heater core stick through the firewall into the engine bay. on some, however, they may not. once you locate the heater hoses, start the vehicle and let it warm up (if it isnt already warm from the previous tests) and feel the heater hoses for heat and/or flow. one of them (the inlet that carries hot coolant into the heater core) should be hotter than the other, but both should be warm (again, be careful not to burn yourself). if the inlet hose is hot and the outlet hose is cold, that suggests a blockage somewhere, either in the hoses or in the heater core itself (most likely). (NOTE: the inlet hose is usually the larger of the two.) if neither hose gets hot/warm and you can feel no flow through them, that suggests a blockage at the engine. so, once you have determined the cause of the heating failure, you can proceed to correct it, either by taking it to a mechanic, or if you have confidence in your mechanical abilities, by doing it yourself. if you decide to do it yourself, go get a Haynes or Chilton repair manual and read it carefully BEFORE you pick up a wrench. be sure you understand it fully before attempting anything. it'll cost you a lot more if a mechanic has to fix your fuckup in addition to repairing the initial problem. (no offense intended by this, just a friendly warning.) ok, I think I covered everything. good luck and let us know how it turns out. final note: with regard to coolant. DO NOT just pour raw coolant (also called antifreeze) straight into the radiator/overflow bottle if you find it low. this stuff is DESIGNED to be mixed with water, at a 50/50 ratio (for most climates, including Tennessee). too high a concentration of coolant CAN cause problems, including engine freeze-up in the dead of winter and/or excess corrosion of the radiator/heater core. ALWAYS mix before you pour it into the system. __________________ He's the best, of course, of all the worst. Some wrong been done, he done it first. -fz I jus' want ta thank you...falettinme...be mice elf...agin...