Overheating when it's freezing...

[feda12]

Hi AZ Members!

I bought a 2006 Audi A4 2.0t this summer with 155k. Everything was running great until today when MN temperature dropped below 0F.

I kept the car in the garage overnight in December so I did not have any issue but I have to keep outside this month.

Last week, I noticed that heat was not kicking in until 5-10 minutes. It was not blowing air and suddenly was heating(both fans and seats).

This morning however, it was impossible to have hot air. Heated seats were working after 5-10 minutes of driving however. When I got downtown, the car started overheating suddenly for 1 minute and then cooled down just as quickly. 5 minutes later, it started overheating again and this time did not cool down until I park.

I am a little worried about driving back, a 15 min commute and as to what this could be? Heater core? Water pump? All of that?

Thank you for your help.

[i3oricua]

Hi AZ Members!

I bought a 2006 Audi A4 2.0t this summer with 155k. Everything was running great until today when MN temperature dropped below 0F.

I kept the car in the garage overnight in December so I did not have any issue but I have to keep outside this month.

Last week, I noticed that heat was not kicking in until 5-10 minutes. It was not blowing air and suddenly was heating(both fans and seats).

This morning however, it was impossible to have hot air. Heated seats were working after 5-10 minutes of driving however. When I got downtown, the car started overheating suddenly for 1 minute and then cooled down just as quickly. 5 minutes later, it started overheating again and this time did not cool down until I park.

I am a little worried about driving back, a 15 min commute and as to what this could be? Heater core? Water pump? All of that?

Thank you for your help.

My first thought is check your coolant level. Make sure you have there right mixture in there if it's low. Yours should be a little more concentrated probably since your winters are so cold. Did you any work recently that requires you to flush your coolant?


Gonzo

[B44]

Most likely its the thermostat. Have you replaced that before?

[feda12]

Thank you for your replies.

The rear coolant flange(as well as the thermostat back there) was replaced early in December by an Audi dealership because it cracked. They flushed the coolant.

Are you talking about the thermostat by the water pump?

[KJack]

Check the easy things first. As mentioned above, check your coolant level. Also buy a coolant tester ($5 at any auto parts store) and make sure you have the proper mix of coolant and water.

[feda12]

Ok, I will do that over lunch and update.

[crazyquik22023]

Thank you for your replies.

The rear coolant flange(as well as the thermostat back there) was replaced early in December by an Audi dealership because it cracked. They flushed the coolant.
There is not thermostat in the rear of the engine.

Are you talking about the thermostat by the water pump?

The only thermostat on the vehicle is the one by the water pump. The problem to me sounds like a faulty thermostat or a failing water pump.

[i3oricua]

The only thermostat on the vehicle is the one by the water pump. The problem to me sounds like a faulty thermostat or a failing water pump.

Both of these are possible but I would def check the mixture first to make sure you're not freezing and cracking your block. You'll have bigger problems of that happens. But like said above, rule the easy stuff out first.


Gonzo

[Jake@JHM]

What mixture of coolant/antifreeze do you have?

[feda12]

Coolant was low/close to none. There was a little bit of coolant on top of the coolant tank, issue with the tank?. Luckily I always keep G13 in my trunk so I added coolant and I will go buy distilled water on my way back to the car. I'll stop to an auto part tonight and check the mixture.

I noticed there was a deposit at the bottom of the tank as well.

[KJack]

Luckily I always keep G13 in my trunk so I added coolant and I will go buy distilled water on my way back to the car. I'll stop to an auto part tonight and check the mixture.

That's good. I do the same thing. I keep an old milk crate in my trunk with a pre-mixed container of G13, quart of oil, jumper cables and other emergency basics.

After you get home check to see if it's leaking somewhere or if it just wasn't filled all the way previously. Also check under your oil filler cap to verify that it hasn't been depleted as the result of a head gasket issue. If your oil cap shows coolant or milky liquid on the underside that would be an issue.

[i3oricua]

Coolant was low/close to none. There was a little bit of coolant on top of the coolant tank, issue with the tank?. Luckily I always keep G13 in my trunk so I added coolant and I will go buy distilled water on my way back to the car. I'll stop to an auto part tonight and check the mixture.

I noticed there was a deposit at the bottom of the tank as well.

I would venture to guess your cooling system wasn't 'burped' after adding coolant. Once you add the coolant and water leave the cap off the coolant reservoir and let the engine warm up until all the bubbles have stopped. Top off as necessary and put the lid on the reservoir.

[BenMTL]

1) Use G12 instead, it's what came with your car.

2) Replace thermastat and/or temp sensors

3) Properly "burp" or air out the system

[KJack]

Use G12 instead, it's what came with your car.

My Audi dealer doesn't even carry G12 anymore. They said it was replaced by G13.

[FraggyA4]

Coolant was low/close to none. There was a little bit of coolant on top of the coolant tank, issue with the tank?. Luckily I always keep G13 in my trunk so I added coolant and I will go buy distilled water on my way back to the car. I'll stop to an auto part tonight and check the mixture.

I noticed there was a deposit at the bottom of the tank as well.

DO NOT POUR DISTILLED WATER IN YOUR COOLANT SYSTEM WITHOUT BEING MIXED FIRST!!!!! If the coolant doesn't get properly mixed the distilled water will freeze. I had this problem last year and ended up having to wait a month for temperatures to get high enough to let the coolant defrost.

Also the thermastats are supposed to fail to open which would cause the car to always be over cooled which is not a problem minus having shitty heat in your car. The heat cycling is most likely a bubble in the system caused from having to little coolant.

Another thing to make sure is to check for leaks. You obviously have one somewhere if you were low on coolant. I would check the hoses coming out of the thermastat and Coolant flange in the rear.

[feda12]

Alright, so I went to buy distilled water and mixed with coolant, went up and down the parking 4 or 5 times(lost count ahah) and there was no overheating so I drove home. Checked the coolant mixture, it is now good until below 37F.

Questions:
1) The RPMs dropped below below the IDLE RPMs when I started, is that "normal" with extreme cold?
2) Sometimes, the air was not blowing hot when IDLEing. Any ideas?

It seems that coolant got below the minimum line after driving for 15 min, there was coolant under the tank. Could the cold have screwed up the tank? I'll top it off tomorrow morning and continue monitoring.

Thank you all for your answers.

[i3oricua]

Alright, so I went to buy distilled water and mixed with coolant, went up and down the parking 4 or 5 times(lost count ahah) and there was no overheating so I drove home. Checked the coolant mixture, it is now good until below 37F.

Questions:
1) The RPMs dropped below below the IDLE RPMs when I started, is that "normal" with extreme cold?
2) Sometimes, the air was not blowing hot when IDLEing. Any ideas?

It seems that coolant got below the minimum line after driving for 15 min, there was coolant under the tank. Could the cold have screwed up the tank? I'll top it off tomorrow morning and continue monitoring.

Thank you all for your answers.

Did you burp the system? Wipe it down and make sure you run it with the cap off the reservoir when the car is warm. Then top it off as it goes low. Its possible you have a leak. I'm not sure about the heater now getting hot, it sounds like your thermostat might be gone; likely getting stuck open not letting your engine get warm enough to blow hot air in the car. Those are my guesses.

[Charles.waite]

My Audi dealer doesn't even carry G12 anymore. They said it was replaced by G13.

This G13 is the new G12.

G13. So hot right now.

[mtroxel]

2) Sometimes, the air was not blowing hot when IDLEing. Any ideas?

This makes me think you have a clogged heater core that had nothing to do with the overheating problems. I live in MN too and can tell you these last few days I've had good heat, even at -10˚ yesterday morning. Its supposed to be in the 20's and 30's for a few days here. I wonder if you can flush out your heater somewhere. Even changing the heater core is not too bad of a job on a B7.

[schmiesus]

The fact you had no heat then way to much makes me think you have either a really big bubble or a thermostat that is really really messed up. And i mean stuck wide open then slamming the door shut when it warms up. I would venture to say check the water pump as well.

[feda12]

Tipped off the coolant this morning, no coolant loss when I got back home.

I burped it as described, I did not see any bubbles coming.

I decided to look more into this heat issue:
- Heat is dependent on the coolant temperature, as soon as the coolants starts warming up(which takes about 5-10 minutes) it then starts blowing hot air and the heated seats heat up as well.
- Air is hot at IDLE when coolant is warm, and cold when coolant is cold.. obviously.

I'll get the heater core flushed at the end of the week(too cold to do it myself).

[crazyquik22023]

I decided to look more into this heat issue:
- Heat is dependent on the coolant temperature, as soon as the coolants starts warming up(which takes about 5-10 minutes) it then starts blowing hot air and the heated seats heat up as well.
- Air is hot at IDLE when coolant is warm, and cold when coolant is cold.. obviously.

How is this an issue? Of course heat is dependent on the coolant temperature. How can you expect to have hot air coming through the HVAC without hot coolant running through the heater core?