Heater Blowing Cold Air

[vevro]

I think i may have my first problem at 135,000 miles. The heater is blowing cold air even when the car is completely warmed up. Before this problem, i would set the climate control at 72 degrees at start up and the hot air would start coming out the vents in small increments at first and then the fan would gradually increase as the car warmed up.

The strangest thing is that on occasion i can get it to blow hot air by waiting until the car is completely warmed up and setting the temperature at Max Hot.

Just want to get some opinions before taking it to the shop. Hoping its something i can fix myself.

[nc211]

I think i may have my first problem at 135,000 miles. The heater is blowing cold air even when the car is completely warmed up. Before this problem, i would set the climate control at 72 degrees at start up and the hot air would start coming out the vents in small increments at first and then the fan would gradually increase as the car warmed up.

The strangest thing is that on occasion i can get it to blow hot air by waiting until the car is completely warmed up and setting the temperature at Max Hot.

Just want to get some opinions before taking it to the shop. Hoping its something i can fix myself.

just a shot in the dark here, but have you checked your coolant level? The resivior tank should be on the passenger side of the engine bay, right around the top of the wheel well. Is it in the right range?

[Sweet95LS400]

That was my guess too. Make sure it is to the full level with a good mix of toyota fluid and distilled water.

[vevro]

:whistles: Alright, so you guys were right, low on coolant. Topped it off with Toyota Red and everything is back to normal. I asked the service guy at the dealership if it was necessary to add distilled water since it was so little that i needed to add and he said it wasn't necessary.

[viclykewhoa]

I think i may have my first problem at 135,000 miles. The heater is blowing cold air even when the car is completely warmed up. Before this problem, i would set the climate control at 72 degrees at start up and the hot air would start coming out the vents in small increments at first and then the fan would gradually increase as the car warmed up.

The strangest thing is that on occasion i can get it to blow hot air by waiting until the car is completely warmed up and setting the temperature at Max Hot.

Just want to get some opinions before taking it to the shop. Hoping its something i can fix myself.

just a shot in the dark here, but have you checked your coolant level? The resivior tank should be on the passenger side of the engine bay, right around the top of the wheel well. Is it in the right range?

I'm a bit of a newbie, so, how would low coolant levels lead to the problem VEVRO was having with his LS? Thanks.

[RFeldes]

It's a "Closed Loop" system you introduce air with low fluid level and it is no longer "Closed Loop"

[wwest]

"vapor-lock" an air bubble blocking flow, can occur in any liquid distribution system.

[RFeldes]

Which brings up a very interesting question....when air is introduced to a closed loop system causing Vapor lock..does the pump go dry and then cycle or does it go dry... period, creating no flow, or is the vapor lock somewhere else ...would that not cause overheating either way? just curious. and probably a simple answer?

[W201 sweden]

Which brings up a very interesting question....when air is introduced to a closed loop system causing Vapor lock..does the pump go dry and then cycle or does it go dry... period, creating no flow, or is the vapor lock somewhere else ...would that not cause overheating either way? just curious. and probably a simple answer?

Hope I did not misunderstand your question, RFeldes:

A sealed (and pressurized!) cooling system will eventually end up almost free from air pockets. If you just circulate water long enough,

air will follow the stream, and end up in the expansion tank. As the air trades place with the water, water level will drop.

This can continue even after several running hours - hence the "topping up" you have to do after a complete flushing of the system.

But since the water pump is fairly low in the system, there is little risk to trap air inside it.

But on some BMW:s, the cylinder head is actually the highest point in the cooling system. (sic!)

Such a design is very senitive to trapped air, and I guess that is a contributing factor to all the cracked heads on those cars...

Hope that answers your question?

/Alexander from Sweden

[RFeldes]

Thanks Alexander, I guess your saying the air stays at or near the reservoir since it's the high point. That would stop or slow the circulation and cause the heater core to not get a constant flow of hot coolant thus cold air....would that not cause overheating? All I hear about is "Blowing Cold Air" but no one mentions overheating.

[wwest]

The smalller the tube/pipe carrying the liquid, versus the liquid's viscosity, the more likely it is that once an air bubble is established, it will not move allong with the liquid flow but remain in the tube as a flow blockage and therefore whatever liquid continues to fluid mus flow around the perimeter of the bubble, resulting in highly restricted flow.

It used to be that the most common occurance of this was in a gasoline line. In the south on an especially hot day the combination of natural heat plus that of the engine having just been shut down would result in boiling the gasoline inside the lines to the carburator. Bubbles in the line would result and when you next tried to start the car it would only idle due to the restricted flow.

Given the relatively low viscosity of coolant the only pipes/tubes small enough to "hold" an air bubble in place and thereby restrict the flow would most likely be in the heater core.

[W201 sweden]

wwest, I think you are comparing apples with oranges here.

Without getting into physical properties of different fluids, like...

A cooling system should not be compared with an overheated fuel line in the summer.

That one actually boils, which is not the case in the heater core! That one is closer to bleeding a brake line.

A good, steady pressure will push the air through the lines, as the air can reach the highest point in the system at the end of the line.

There is no actual boiling or vapour lock.

That CAN happen, but normally only with a blown head gasket or similar problems.

I recently changed the heater core in my MB, and it took several days until the

bubbling sound from the heater at start up was fully gone - which is normal.

By the way: Also almost all diesel engines will EVENTUALLY evacuate the fuel lines, the air bubbles WILL go with the flow, not sooner but later... ;)

/Alexander

[wwest]

I was by no means using the gasoline boiling to explain how an air bubble got into the engine coolant system, I thought that had been well covered already. I have overhauled not just a few engines in my lifetime and was always careful to monitor the cooling system for inadvertant "vapor locks", coolant voids, after I put things back together and then refilled the cooling system.

"...it took several days...." "...which is normal..."

???

Absolutely not!

If you are hearing bubbling sounds in the coolant flow that means that you're still pumping air along with coolant. In that case there is a significant danger that a large air bubble will become "lodged", say within a cylinder head, and now you can end up with really serious problems.

And by the way, fuel pumps for diesel engines run an extremely high pressure level, so yes, vapor lock, when and if it happens, is a relative short term thing. On the other hand fuel pumps to fill a carburator fuel bowl ran/run at what, 2 or 3 PSI ??

[W201 sweden]

This time I will try to stay on topic... ;)

Why low water level can stop the heater from working:

If the water level goes down, air will enter the system. The air will form bubbles that sit on "high points" in the system. IE, if there is a pipe shaped lika an upside down "U", (the oppostie of a "water lock" under the sink) there will be some air in the highest point.

When you start circulating the coolant, water level will rise in the pressure side of the U-bend. Coolant level will rise, until it is high enough to flow over the peak, and drop down on the other side. Circulation starts, although a bit randomly (exp?). If the system water level is too low, local level in the pipe will not rise high enough to initiate a flow => no heating in your case.

If you have a steady circulation of pressurized, "air-bubble" free coolant to that U-bend, the air trapped in the pipe gets "washed out" little by little.

The case with the heater core is similar, but there can be a twist to it. If the design is such, that there

is a closed cavity in the core, which extends higher than the highest points in the outlet, one more thing happens.

The air bubble in the core is basically "floating" on top of the water surface in the core. As the pressure in the cooling system builds up, the small bubble in the core will shrink

(PV=nrt anyone?). This means the water level in element will rise, to the point of fully "occupying" the exit hole. That makes it harder for the small bubble to "reach" the exit opening and float away. The next time the coolant pressure is down, the air bubble expands again, (although not reaching its previous size) and some more air easily "escapes" - with a slight sound. So, the heater core can (and will often) have a bubbling sound during warm-ups (and only then) for some days after a draining/refilling of the system - dependent of your temperature and driving conditions.

So it's normal.

As a consequence of this - if you suddenly start to hear a bubbling sound after start up, you can suspect you have got a leak in the system.

These factors are dependent on specific design, so some cars exhibit these symptoms, while other don't.

Thanks for reading all the way down here. :)

/Alexander from Sweden