Suddenly no heat when engine's warm

[ValgeKotkas]

So recently the heater stopped blowing hot air when the engine got warm.
Interesting thing is that it blows warm air until the engine warms up, but if I'm not mistaken, only from the windshield vent. After that I get only cold air from everywhere

At first I thought it's the valve in the engine compartment, cause the arm didn't move when blowing changed from cold to hot. I tried out my spare one (plugged everything in but the coolant hoses - it worked. Next day the same thing, the arm in the valve doesn't move...).

I'm thinking maybe a sensor? Anything special I could check?


Thanks in advance.

 

[madsupra88]

You have air in your coolant system.

 

[ValgeKotkas]

Shouldn´t the system be self-burping?

 

[madsupra88]

Sometimes u get air pockets in there. just burp the system n see what happens.

 

[ValgeKotkas]

Tried it, and with no luck.
Also tried playing with the valve in the engine compartment. It sometimes works, but usually doesn't (valve arm out when blower put on cold (where it usually stays and doesn't move no matter what position the heater control is in) and arm in when on hot).
Got the valve working a couple of times when played with a finger on the vacuum of cruisecontrol, but this method also didn't work always.
Putting the fans on Auto and playing with the heatknob doesn't change anything. System always blows on maximum, though it shouldn't do it throught the whole temperature range.

Any other suggestions?

 

[rayall01]

Tried it, and with no luck.
Also tried playing with the valve in the engine compartment. It sometimes works, but usually doesn't (valve arm out when blower put on cold (where it usually stays and doesn't move no matter what position the heater control is in) and arm in when on hot).
Got the valve working a couple of times when played with a finger on the vacuum of cruisecontrol, but this method also didn't work always.
Putting the fans on Auto and playing with the heatknob doesn't change anything. System always blows on maximum, though it shouldn't do it throught the whole temperature range.

Any other suggestions?

Look at the valve, and find the vacuum connections, bypass the electronic part of the valve and run vacuum directly to the mechanical part of the valve. If that solves your problem, you can leave it like that, or replace the valve, which is pretty pricey.

 

[madsupra88]

If you test and find out its your valve, i have one for cheap

 

[ValgeKotkas]

Tried the direct vacuum, the valve retracts the arm, but it just blows the same warm/cold air it blew before. WTF moment... The damn system is killing me. I guess I should try tomorrow one more time.

 

[rayall01]

Well someone has to say it, so I guess I will. You sir, may be experiencing the dreaded BHG! I hope it's not, but you should be prepared for a worst case scenario.

 

[madsupra88]

I still think you have air in your system! some how it got there, small leay maybe somewhere, bad rad cap, er hopefully not a leaky head gasket.

Has the car EVER over heated on you before?

 

[ValgeKotkas]

The engine has been redone two years ago. And why I'm starting to believe madsupra is maybe right is that just after the first start, there was this rumbling behind the dash (as it was before the job) that I couldn't get out. I'm guessing it was air.
And nope, no overheating. The temps stay always at 1/3 on the gauge, +- a bit.
The rad cap is an idea. It is probably 23 years old, though the rad is new :icon_razz So I'll look into changing it.

 

[rayall01]

It's the suddenness of the problem that has me thinking BHG, kinda like you pumped a large amount of air or exhaust into the coolant. If that valve isn't the culprit, it seems too sudden to be a cap, or leak.

 

[madsupra88]

To rule them out, i would first check the small stuff before tearing into the motor.

 

[rayall01]

To rule them out, i would first check the small stuff before tearing into the motor.

Certainly, that would be prudent. I'm just being devils advocate to prepare him for the worst, if it should actually be a BHG.

 

[jdub]

Guys - Not everything is because of a BHG. Think about this: Air would have no impact on whether the heater control valve opened or not and air stands no chance of blocking coolant flow to the heater core. In addition, coolant is fed from the back of the head to the heater core. You would have to have an awful lot of air in the system to lower the coolant level to the point where it stops flow to the heater...the car would definitely overheat.

There's no point in playing "devils advocate" and getting the guy to start seeing ghosts.

Sounds like to me the heater control valve is bad (yes, the 2nd one too) or there is insufficient vac to open it. Could be a problem with the wiring from and/or the climate control as well.

 

[madsupra88]

Guys - Not everything is because of a BHG. Think about this: Air would have no impact on whether the heater control valve opened or not and air stands no chance of blocking coolant flow to the heater core. In addition, coolant is fed from the back of the head to the heater core. You would have to have an awful lot of air in the system to lower the coolant level to the point where it stops flow to the heater...the car would definitely overheat.

There's no point in playing "devils advocate" and getting the guy to start seeing ghosts.

Sounds like to me the heater control valve is bad (yes, the 2nd one too) or there is insufficient vac to open it. Could be a problem with the wiring from and/or the climate control as well.

Jdub,

If you test out the heater valves (if he did it right that is) and they both test out good. There is deffinatly air in the system. it doesnt have to be a bhg or too much air. If you have air in your coolant system, you wont have warm air, it may come back for a few seconds but then it would go back to cool air.

Happened to me numerous times with my supra and the benz.

Luckily for me i just had a pin hole in my heater hose.

 

[jdub]

In my experience, (including fixing BHGs, complete coolant drains, replacement of heater cores, etc) I have never had to "burp" the system. It has always eliminated the air on it's own over several days. That also includes other Toyota cars that use a similar heating system. If air is getting trapped, something is wrong with the coolant system. I'm not convinced air is the problem.

If you re-read his posts, when he applied direct vac the heater control valve arm worked, but was hit/miss in the normal configuration. Hence what I said about the vac line or the climate control.

A sure fire way to eliminate coolant flow through the heater control valve as a cause would be to bypass it by placing a correct diameter metal tube between the hoses.

 

[zuf]

hi there had the same problem and it was a dry joint in the heater cotrol
i took mine out re soldered the joints and it work fine if you remove the cig tray and
move the wires when the engine is warm and running it will start to blow warm
hope this helps

zuf

 

[ValgeKotkas]

Took the CC out and all the pins and solders looked OK. Tried it out and everything seemed to work better (didn't warm the car up though). We'll see what happens tomorrow when I try it out to the max.
Thanks a lot for now!

E: So tried it out, and the problem persists. I think it´s not a problem of CC nor the valve (Everything works PERFECTLY until op. temps are reached - then even giving the valve permanent vacuum doesn´t help). I can´t understand how air could be the problem also in this case? If air would be in the system, shouldn´t it make the problem permanent so to speak?
Is there a sensor for CC that has something to do with coolant temperature?
I don´t remember any sensors in the heatercore itself, problem probably isn´t there ?

 

[Island_Yota]

My car has the same kind of issue, In mine its air in the system. If I burp the system its fine for a couple days, no waterfall sound behind the dash but it eventually comes back, Ive checked everything, replaced the rad cap, thermostat, all of the overflow hoses are tight sealed, pressure tested the cooling system it all seems fine. I even replaced the heater core last year because it blew so its not leaking there either.. I soldered the hard pipes and pressure tested it before it went in the car. I burp the coolant every couple of months because of this, the coolant level never goes down.

But, my heat does work. Its just once in awhile when the cars just warming up, it will have heat, then it will disappear until the thermostat cycles again and then its back and stays blowing hot.

its a mystery.. and my way of solving it is the 7MGTE in my garage :icon_razz