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heater blowing cold air please help

34K views 25 replies 11 participants last post by  peva 
#1 ·
I just bought a 2004 dodge intrepid with 110,000 miles on it. Whe you turn the heater on it just blows cold air no heat. I thought it might be the thermastat but the car is not getting hot. any ideas?
 
#2 ·
It could still be the thermastat. A bad thermastat dosen't allow the car to get up to operating temprature. Check to see that you have enough coolant, and that the air is bled out of the cooling system. If its still not getting warm change the themastat, its like $10 and easy as pie
 
#3 ·
By the ay, the air is bled by means of opening the bleeder valve that is on the thermastat housing. Do you really need heat in Kentucky?
 
#8 · (Edited)
Check the coolant level as mentioned. If its low, and its a 2.7, check the water pump for leaks immediately. In fact, dont drive it until you know the water pump is good. Drive the car for at least 20 minutes, and come back and feel the hoses. Upper and lower radiator hoses should be hot, and both heater hoses should be hot.

If you have any cold hoses, the thermostat is sticking open. If all hoses are hot, then the problem is in the heating system. It could either be the blend door actuator, that opens/closes the hot/cold air door, or the heater core is plugged. Next step would be to remove the actuator, and manually move the door to the hot position. If you still have no heat, replace the heater core.

If its a 3.5, with 110K miles, it would be a good time to replace the timing belt/water pump unless you know its been done already.
 
#9 ·
Follow Daytrepper info above...Don't forget to bleed the air out of it if you have to add any coolant.......If it is a 2.7 engine keep a close eye on the coolant level and oil level and oil consistancy....Just being about 1/2pint low on coolant will make it loose heat..

And WELCOME to another member from Kentucky....GO CATS!!

Good Luck!!
 
#10 · (Edited)
If it is a 2.7, be very gentle with that bleeder when opening and closing it. Only tighten it enough to totally shut it off - no more than that. The bleeder is a metal insert molded into the plastic housing and is famous for totally coming out of the plastic.
 
#11 ·
I found that if you take the temp control and lower in down and then raise it up to HI that works for me. My door sicks not allowing heat into the car. when this didn't work I checked my heater core and it was plugged. Now I'm a older car type of person I know nothing of new cars. But I reversed the flow of the coolant and blew out the heater core. Old trick and it still worked....in this case.... hope it gets you warm...
 
#12 ·
How do you check the waterpump on a 2.7? and why would low coolant cause the heat not to work?
My hot air just started blowing cold as well. It will eventually start to blow hot but only after it has been driven for a while (much longer than normal). I think it might be the thermostat though because it does the same thing (the opposite) in the summer. In the summer the cold blows hot.
 
#13 ·
There is a weep hole, at the lower left of the thermostat housing, if its leaking, water pump is gone. If there are no other leaks, no heat at slow speeds, or idle is a dead giveaway, that there is a water pump issue. Low coolant will cause no heat at idle...have it pressure tested to check the rest of the system for leaks, and if the water pump is found to be leaking, park it until it can be fixed...it can destroy the engine.

As far as checking the thermostat, feel the hoses after the temp gauge indicates normal temp. If the lower hose is cold, little/no heat, likely the thermostat is stuck open.
 
#20 · (Edited)
So stuck OPEN thermostat would give max flow (mass) to the heat exchanger (rad) and the HX would cool the coolant to a maximum amount of its design.
The coolant leaves the HX quite cool (over cooled) and goes back into the engine to accept more heat. The coolant accepts more sensible heat and next to no latent heat and heads back to the HX. The HX working at max efficiency (especially in the cold air) gets rid of the sensible heat easy and fast and under cools the coolant in respect to its intended design.
I can see it happening although I have not wittnessed it.( Auto mechanics is not my carrer)
Different engines will have different characteristics.
Ive heard the old Ford 351 Cleavland will overheat when the T-Stat is removed because the coolant will go thur the engine, without that physical restriction, so fast it will not accept the heat of the engine.
As Peva said: interesting.
 
#21 ·
Different engines will have different characteristics.
Ive heard the old Ford 351 Cleavland will overheat when the T-Stat is removed because the coolant will go thur the engine, without that physical restriction, so fast it will not accept the heat of the engine.
As Peva said: interesting.
This is true. They all react differently. Depends on the design. Some engines will run stone cold with the t-stat stuck open. These tend to show normal op temp due to the location of the sensor.

A 350 Chevy will run stone cold, same as a 3.1 GM. Not sure on the 351, never witnessed that.
 
#23 ·
I dont know if the old 351C story is true or not either, but I can belive it happening
I think it would be alike if I moved my hand (1kg water) quickly thru a candle lit flame (engine)
My hand would not pick up too much heat (hopefully)

Just a quick reference to my "Basic Engineering Thermodynamics" by Rayner Joel
Defining the adiabatic process (Q=0)
"................if a process is carried out with sufficient rapidity, there will be little time for heat transfer."

And I seem to remembe something about a laminar area next to the solid that has to do with heat transfer. Cant remember right now. Anyhow, not important right now.

Nice to look into the old thermo books agian. And know Im not going to be tested next week.
Peva...???... you're not going to test me are you?
This is all for fun right? :)
 
#24 · (Edited)
Yeah - I'm furious. :)

On your moving-the-hand-thru-the-flame thing, here's the fallacy: You have to look at the continuous flow of water as an infinite number of hands moving in rapid succession thru the flame. The amount of heat transferred into all the hands will equal the same as the heat transferred into the one hand if it were kept in the flame. With the many hands moving thru the flame, each hand would heat up a negligible amount, but the total heat taken from the flame by all the hands will be the same as the one hand if it were to sit in the flame. Moving one hand thru the flame, and that's it, is not the same. Your hand analogy was as if you threw a pan of water onto the engine and that was it. You're moving water constantly thru it - hence my countering with the infinite-hands-thru-the-flame analogy.

And actually the many hands thru the flame thing would transfer more heat than one hand sitting in the flame because the new hands coming along would be colder than the one hand that is heating up - and as you know heat transfer increases with greater temperature difference.

On your Joel quote, I'd have to see his complete statement, but is he saying the rapid process like your single hand moving thru the flame? If so, again, that dosn't work because, again, to extend your analogy, it is infinite flow of hands thru the flame.

Look at it this way: All the engine metal knows is that there's a certain mass of water in contact with it, and the temperature difference is 'X' - it does not know if it's still or moving slowly or moving rapidly. But, the moving water will cool better because it doesn't rise in temperature as much as the water sitting still against the hot metal. If it's moving, a given molecule of water will heat a little and move on. When it returns, it will have gone thru the radiator and cooled down a little. The same molecule of water sitting still at the same place will heat up, and the heat transfer rate will decrease because the temp. difference is decreasing - the water is getting hotter while the metal is cooling. With the moving water, the metal is cooling, but the water is not heating up nearly as much - so greater maintained temp. difference, greater rate of heat transfer, end result is cooler metal.

There's also limits (think "Calculus) involved in the process that makes it a little difficult for the untrained mind to think it thru to the ultimate steady state conclusion, but the end result is that the faster the water is moving, the better the cooling - primarily due to that greater temperature difference thing.
 
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