volman5

I'm #@%*ing freezing because of a heater problem. I have an '88 Mazada MX-6. The heater fan works but no real heat is produced. Anybody have any ideas?

GSRIDER

i can't tell you how to fix it but the problem is most likely your thermometer... i had the same problem in my old old car.

if you have your manual take a look at that and see if it's a quick fix.

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mazak

first make sure the coolant is full. then there are 2 hoses going into the fire wall to the heater core are they both hot? if not the heater core is most likely plugged up. not letting the coolant flow. when was the themostat changed last it might be stuck.good luck. also on some vehicles there is a heater control valve , its located near the fire wall,if its not opening it wont let coolant flow to the heater core.autozone.com has pictures as well as a component locator

Sion

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.

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Bigwahzoo

Wow Sion you really put a lot of time into explaining the entire cooling system of a car. Keep up the good work!

Peryn

Yes, very detailed and accurate description of the heating/cooling system. Typically, those heater hoses ar going into the passenger side of the cabin, and (i have found) have metal "hoses" coming through the firewall. If you cant find your coolant lines, try looking for a few large, metal hoses coming through the firewall.


On a kinda semi-related note...had to replace the heater core on our '89 S10 Blazer today. Damn....thing was a pain in the ass. Had to undo all sorts of bolts and connections, and move the friggin dash outta the way to get the cover off. I never stop being amazed at how many bolts they manage to put into holding a dash on... After that its a piece of cake. Now i just gotta get it all put back together

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shakran

Dang Sion, I thought I wrote long posts. Nice explanation. Very detailed and completely accurate.

You did forget one possibility, though: (technically 2, but they're both the same failure)

There are (on most cars) two valves that are moved by wires when you turn the temperature dial up. Depending on the car, the cables could be attached to the dial or the dial could activate motors that move the wires for you. Either way, the two valves are opened by wires. This is good because it lets you trace where the valves are. One will be inside, usually under the dash on the passenger side somewhere. The other will be outside on the upper heater hose. That one's the valve that directs coolant through the heater. If either one of these valves gets stuck, you won't have a properly working heater. Watch the valves as someone turns the dial. If they move, you're OK. If only one moves, fix the other one.

Sion

shakran, while I dont know about Volman's Mazda (I have very little hands on experience with that brand) I can tell you that what you are refering to is very rare on american cars. I've owned more than half a dozen cars and worked on hundreds more and dont think I've ever seen a setup like that. not to say it doesnt exist, just that I've never seen, worked on, or sold parts for such a complicated control system. mostly, the coolant flows through the heater core at all times, and the control is in dash and either prevents or allows air to pass over/through the heater core and into the cabin.

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volman5

Damn thorough explanation Sion--Gracias! I will attempt to utilize the plethora of knowledge you have provided sometime today. I got to busy with football this weekend to make it out of the house very much. Best playoff games I can remember seeing!

shakran

Sion:

Yeah, I'm more referring to Japanese cars. You see this system a lot on them.

Of course, they also stick the ignitor/coil INSIDE the distributor so they do things a little differently

Peryn

Yeah, on the American cars I've worked on, they pretty much only have some sort of switch (electric, vacuum, whatever) to let air flow or not, thats it. His Mazda could be far more complicated.

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volman5

Ok. This is what I've discovered: The inlet and outlet hoses on the firewall are very warm, the upper radiator hose is hot--yet the lower radiator hose is cool and the car isn't over heating. I don't get it!

GSRIDER

schooled.

I'm always messing those up.

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mazak

just a thought but bring it to a radiator shop and have it flushed sounds like a clogged radiator or cooling system.good luck!!!

Ashton

Sion

I think Ashton has it nailed.

is the switch for heat a knob that turns, a button thats pushed or a slide switch. that should tell what sort of control for the flap the vehicle has.

then we can tell you what to look for when you crawl up under the dash.

__________________
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...

volman5

It's a slide set up. I think I'll have someone do that for me to avoid the fuck-up factor. I'm not intimidated too much by minor engine work but dash dismantling is out of my league. Muchos Gracias for all the help. If you're ever in Knoxville I'll buy everyone a beer or a few.

james t kirk

Had a car once where the heater core got all bunged up.

Took of the heater hoses and gave it an enema and bam, it worked much better.

Nice post scion by the way.

Peryn

Once you figure out how it works, and how to test it...id say give it a try yourself before bringing into a shop. Worst case : You fuck up and hafta have the shop fix it for ya anyway...

BUT, since it doesn't sound like its the heater core itself, you probably wont hafta pay too much. Just pay them for diagnoses ( if you think you can fix it). Once you know what to look for, and how to fix it, its not too bad crawling under the dash. But might be well worth it for them to figure it out for ya.

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