Heater not getting hot

Asked by Oct 09, 2012 at 12:00 PM about the 2005 Pontiac Grand Prix GT

Question type: Maintenance & Repair

I have a 2005 pontiac grand prix.  Heater fan works, but blows cool air.  We replaced the thermostat but that didn't make a difference.  What else could be wrong besides the heater core?  Is there any easy way to tell if it's the heater core or could it be something else?

24 Answers


if both hose to the heater core are hot and the heater core is not leaking there is probly nothing wrong with the heater core . I would check to see if the diverter door is working . it usually works on vaccume and changes the dirrection of the air flow from vent to heat or ac when called for

36 out of 36 people think this is helpful.

if the diverter doors are not working. check for a vaccume problem. or possible control is not working properly

17 out of 17 people think this is helpful.

if you have the optional heater and a/c controls, the temp is contolled by a sensor located in front of the radiator. i had an 02 bonneville that needed that sensor replaced to fix heat and ac

15 out of 15 people think this is helpful.

First check your coolant levels and make sure there is no air in the cooling system. Low coolant levels can sometimes cause the heat to not work and it's a cheap fix.

20 out of 20 people think this is helpful.

if the temp on your heater control is not reading correctly, say its 30 degrees outside and the temp reads 80 that sensor needs to be replaced, that is if you have the optional electronic temp controoled heater and a/c

8 out of 8 people think this is helpful.

I had a similar issue to this on my 2006 Grand Prix. After painstakingly removing the glove box to look at the blend door actuator, I found it to be working normally. In hindsight, I didn't need to do all of that work, because I could actually hear the actuator working when I changed the temp control knob. You should be able to hear it run and bottom out when you are all the way cold or all the way hot. This shows that both the actuator is working and the blend door is not jammed. My next step will be inspecting the heater control valve, and I am confident that this will fix it.

23 out of 23 people think this is helpful.

cant get no cold air from vents in 95 pontiac firebird

4 out of 4 people think this is helpful.

clogged heater core . dexacool clays up in heater core . remove both lines to core and take a small blow gun and place it in one of the holes and cover the other slightly to prevent spraying and let the air rip through to blow out the clog !!!!!

15 out of 15 people think this is helpful.

I just got ripped by a mechanic for this very same issue. 2009 Pontiac no heat , after the mechanic took my dash apart just to find out what we already told him (nothing wrong with heater core) they then found a crimp in my hose charged me 461.61

3 out of 3 people think this is helpful.

head gasket is blown im changing mine out right now

3 out of 3 people think this is helpful.

pontiac 3400 enjins are known for head gaskets going out internally

1 out of 1 people think this is helpful.

What other symptoms show the head gaskets if going out?

16 out of 16 people think this is helpful.

How do you check the diverter doors?

61 out of 61 people think this is helpful.

For people that have problems with there car not getting heat. I haven't had heat in my car for 5 years. I have change the water pump, thermostat, and radiator. Most likely what happen is someone mixed 2 different kinds of coolant and it created a orange clay that clogs the radiator and the heater core. If u have this orange clay in your car, u will go threw hell to get this fixed. First off u need a new radiator, cause there is no way u r going to get it clean, I tried. When u install the radiator do not connect it to your cooling system yet. Next, flush the inside of the engine with hot water, when flushing, take a break and let hot water sit in the engine to help break down the orange clay, and keep flushing out. This will take awhile. Then splice the heater core lines, and get connectors to put the heater core back together. Now I got muriatic acid and I poured about 3/4 of a cup down in the heater core and had pressured hot water ready to shoot threw the line after u pour the acid in. Do not let that acid sit in there, if u leave the acid in too long it will ruin the heater core. After u flush the acid out, have a air hose to shoot threw the line and shoot all the water out. Keep putting hot water in the heater core and blowing out. I shoot the water in the inlet and after I did that, I switch to the outlet. I did this about 30 times. 15 for the inlet and 15 for the outlet. This should fix your heater problem. That orange Dex cool is junk and will never have that in any of my vehicle. GL and I hope this solves your problem.

3 out of 3 people think this is helpful.

It's good to know that. I've been calling what was in the radiator something like oatmeal but orange clay describes it as well. Got tired of having the radiator flushed and it making no difference so you pretty much described my problem better than anyone has. Now the big problem is the ability to fix this. It's cold here and that sounds as thought it takes time a bit of money. Wanted to keep this car as it would be a classic someday but I think I'm going to have to trade it. Benn using son's car on really cold days. Thank goodness we don't work on same days. Can't get the defroster to clear the windows without the hear and it's only a matter of time before a wreck or ticket..

1 out of 1 people think this is helpful.

I spent about $230 on the parts for the car. $10 for the acid, u can get it at a Lowe's, Home depot, or a hardware store. I did all the work myself. I been a contractor the last 20 years and experience in some plunging and I used plumbing parts for the flushing. Yes 6 degrees outside causes a problem. The whole process took me about 3 hours except for the water pump I did that a couple of days before hand. Even if u do one thing per day to get it done, I guarantee it will work. I been dealing with this for 5 years and this solution worked.

2 out of 2 people think this is helpful.

Have already changed the water pump. Flushed the radiator several times but no one could give me an answer on what I called the oatmeal that built up in the radiator but as I said, your explanation of orange clay works to. Just once I would have like to hear someone say, "That beats the dickens out of me; I don't know what it is." Instead it was just to tell me to flush the radiator every couple of weeks. I could flush it forever, but that stuff would build up again. Or they're have some other expensive answer. Some were so stupid I knew they wouldn't work. I tried some on my own and took it to a garage a couple of times. I'd like to try this but may have to wait until it gets warmer. Just drive my sons car in the meantime. Hopefully, I can get it fixed in a little over a year instead of five but I appreciate the answer. That water pump won't have to be changed again will it?


No, u shouldn't have to change the water pump again. I would try what I did to the heater core. U might be able to get the heater to work for the winter before it clogs up again. Then when u get a chance to fix it right. U have to get all that out of there and once it's in the radiator u can't get it out.

2 out of 2 people think this is helpful.

And don't ever use dex cool again it's junk, stay with the green stuff

1 out of 1 people think this is helpful.

The cup links u will need for the heater core hoses r 5/8 so u r not guessing which ones u will need


Thanks so much. Sounds like this might really work. Thanks for sharing your experience. Strange that they recommend the dex cool but I'll listen to the voice of experience.


Np, hope everything works out. Good luck


My 98 grand am gt when trying to turn knob to highest level to defrost not working but it works on lowest level which is three help

1 out of 1 people think this is helpful.

To everyone who tried to help me, a big thank you. That car was costing me money every month. I was freezing, burning up, or the car was overheating or getting wet inside. I felt like I rebuilt that car but the check engine light still came on at least once a month and the heater was not working. I gave up and traded for another car. I don't think my car payment is as high as the upkeep on that Pontiac. Too bad - it was a cool looking car and had it's moments of being great but I couldn't afford it anymore. Again, thank to everyone.

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