No heat when I come to a stop

[Grifter]

Now that its cold in MN, I finally get to use the heat.
When I am driving down the road, the heat blows just fine, nice and hot. When I come to a stop, it blows very cold. Once i start moving again, its hot again..

Whats the deal?

[OneBADLsE]

Thermostat??? Sounds like a good guess to me.

[prchrman]

On old vehicles (maybe new) the heat core valve was ran by vacuum and if there was low vacuum it would not stay open...also if the water pump is going it does not have enough pressure to make the coolant run through the heater core...low coolant level is also a big possibility...and like above, thermostat...willie

[jdando]

air in the system?

What does the engine temperature gauge read? Mine points to 20mph on the speedometer when warmed up. Is yours varying?

jeremy :snowman:

[Zack]

Now that its cold in MN, I finally get to use the heat.
When I am driving down the road, the heat blows just fine, nice and hot. When I come to a stop, it blows very cold. Once i start moving again, its hot again..

Whats the deal?

You have air in the system.
I have found the easy way of removing it is to get the car nice and hot, then park it overnight with the cap to the reservoir REMOVED.
If the coolant level drops in the morning, it worked.
Place the cap on the console so you dont forget to reinstall it!

[fastblackmerc]

On old vehicles (maybe new) the heat core valve was ran by vacuum and if there was low vacuum it would not stay open...also if the water pump is going it does not have enough pressure to make the coolant run through the heater core...low coolant level is also a big possibility...and like above, thermostat...willie
I could be wrong but.......

I believe this is incorrect. If you lose vacuum the heater valve will stay open, your temp setting will be on high and you'll get all your heat out the defroster. Cars have had this type of failsafe system for years. This is so your windshield stays clear so you can see.

[Grifter]

i was thinking there might be some air in the system. according to my OASIS the previous owner had it in for that under warranty.
i have never had a vehicle that has done this, so i didnt know if it was a symptom of that or not

[fastblackmerc]

Yes, your symptom sounds like air in the cooling system, see Zack's post above.

[Grifter]

Thanks guys. I will try it out tonite when i get home.
Opening the reservior cap while hot, its going to spray everywhere wont it?
i dont need a trip to the burn unit.. LOL

[Bill Lalk]

I have had constant problems with air in my system. I was told to jack up the front end to help the air rise to the high point to escape - bleeder tube plug when cold(overnight) and reservoir cap when hot. Make any sense??

[Grifter]

so if the car is cold, open the crossover tube cap, if its hot open the cap?
Elevating the front is a good idea. I could just drive it up on ramps.. might as well do the oil while its up :D

[Zack]

I dont think you need to jack it up, but it might not hurt.
When the car is hot, just ease the reservoir cap off (car off) and relieve the pressure. It wont spray everywhere.

[RF Overlord]

^^^what Zack said^^^

DON'T remove the crossover tube cap when the motor is hot!!

With the motor cool, remove the crossover tube cap and see if there's coolant in the tube. If necessary add coolant through the crossover tube bung until it's full, then install the cap loosely, just a couple of threads. Start the car and let it idle until it warms up. When air has finished fizzing and burping out the cap, tighten it up. Walla...no more air pocket.

[CRUZTAKER]

^^^what Zack said^^^

With the motor cool, remove the crossover tube cap and see if there's coolant in the tube. If necessary add coolant through the crossover tube bung until it's full, then install the cap loosely, just a couple of threads. Start the car and let it idle until it warms up. When air has finished fizzing and burping out the cap, tighten it up. Walla...no more air pocket.

I was always able to bleed the air by merely loosening the crossover nut (not removing) and waiting for the fizz to stop while the car idled warm as well.

As a side note, when my car started to blow warm air on and off eratically last fall, it was a bad thermostat.

That has been the only failure on the entire car in 4 years/42,000 miles. The thermostat. And get this...it was the aftermarket cooler stat I got when I first joined the site.

The dealer replaced it under warranty....with another cooler stat.
I have a really cool dealer.

[Jon01]

Mine's doing the same thing, I have a feeling it's the ATC controls, I'm only getting defrost output also all of a sudden. Putting it in neutral and bringing it up to about 2k at a stop, see if things warm back up. Mine does. Going to be replacing the ATC controls next weekend, I'll post back if it fixes that issue also.

[Bill Lalk]

^^^what Zack said^^^

DON'T remove the crossover tube cap when the motor is hot!!

With the motor cool, remove the crossover tube cap and see if there's coolant in the tube. If necessary add coolant through the crossover tube bung until it's full, then install the cap loosely, just a couple of threads. Start the car and let it idle until it warms up. When air has finished fizzing and burping out the cap, tighten it up. Walla...no more air pocket.

RF, Do you think raising the front end will help anything? I was told that trick by a couple of Mustang guys. I am going to try your method this weekend to try to eliminate my cronic under dash area girgling noise. Car never overheats, all A/C and heater functions never a problem, just the under dash girgling noise. Whenever I jack up frt, remove crossover plug and let it set overnight, the girgling goes away for a week or two, then very slowly comes back over time.
If I wait to long on warmup, will it start to spray out coolant/antifreeze or is that the whole point.:dunno:

[RF Overlord]

Bill, the crossover bung is actually the highest part of the cooling system already, so raising the front shouldn't be necessary, but I can't see how it would hurt anything.


If I wait to long on warmup, will it start to spray out coolant/antifreeze or is that the whole point.It will kind of spit and fizzle, but it won't actually spray coolant at you. Once all the air is out, the spitting and fizzing will stop and that's when you tighten the crossover cap.

[Bill Lalk]

Thanks RF, I'll give it a whirl on Sunday and let you know in a couple weeks if my air bubble problems are done.

[Marauder2005]

I had this problem all the time. Went threw three thermostats in 2 years

of ownership. Sounds like a thermostat to me.

[Grifter]

it comes up to temp fine, and doesnt drop back down. the temp needle points at the 20mph spot on the speedo..

I think the previous owner put in a lower temp tstat anyway.

[jerrym3]

I have a similar but different problem with my 94 TBird.

Thermo is good, car temp is good, but heat is lukewarm.

And, I can hear what sounds like a door under the glovebox opening and closing every now and then when the heater is on.

Also, when I hear the door moving, the voiltmeter drops and then goes right back to normal.

Any ideas?

[SID210SA]

Is it like a creeking door like in an old scary movie? I have that creeking door syndrome....but no heating problems...although I have noticed a clicking sound now when I turn on the floor/def button.....only sometimes though. Kind of like something like a straw in a small fan....

[Grifter]

that would probably be your blend door you hear..

new twist to this problem this morning, and again at lunch.

When i first start the car up, the temp gauge climbs to within 1/4" of H, then then finally drops. Until then I have no hot air at all coming through the vents. When it finally drops, hot air then comes out and the temp returns to normal and then stays there.

Sounds like a sticking thermostat now i think..

[jerrym3]

Blend door sounds correct.

If I let my fan run on the lowest possibel speed, I will get decent heat after a while. If I run the fan on high speed, the heated air gets cooler immediately. I imagine that by running the fan low, the air has time to gain a higher temp before it's pushed into the car.

How does one correct the blend door issue?

If I have to pull the dash, ain't doing it.

Did it once in my wife's 1981 Fairmont wagon to change the heater core, and swore I would never do it again.

[Jon01]

Stuck a new ATC controller in mine last weekend and haven't had the problem yet...but it hasn't been as cold either, lows in the 30's. I'll post back if the problem returns when it gets colder.

[Grifter]

i did as described above. filled through the crossover tube, left it loose, let it fizz for a while. good bye air pockets..

it seems to be quite happy now. Thanks very much guys.