A4 Heat Problems, Should be an easy one!

[Avant1.8BT]

Hey guys, my friend recently picked up a B6 A4 for a daily driver and loves it. One problem, the heat isn't working.

Any input is appreciated! Here are some facts!

2003 A4 1.8t 170k


I have taken the hoses off the heater core, ran water/vacuumed it out. does not seem to be clogged. I poor water through it, watch it run out.

The car takes a very long time to heat up.

Both the hoses on the heater core do not get hot, they stay Ice cold. I follow them down and they slowly get warmer a little warmer, but that hot at all.


So, Is the heater core clogged and the water pump doesn't have enough power to push the water?

Is my thermostat stuck closed? not allowing water to flow though out the car?


I want to work on it today, figured I would ask you guys before we got back at it.

Thanks and happy new year!

[old guy]

How long does it take for your temperature gauge to reach the 12:00 position?

[Avant1.8BT]

How long does it take for your temperature gauge to reach the 12:00 position?

With the car idling, 10-15 minutes... Thermostat stuck open?

[old guy]

With the car idling, 10-15 minutes... Thermostat stuck open?

At the next cold start don't let your car idle for that long. Give it 1 minute to warm up and then drive it gently. It should reach full temperature in no more than 5 minutes. However, if your temperature gauge is eventually getting the the 12:00 position you should then have heat. If the engine is at temperature but you don't have heat and the heater core supply/return hoses are still cold either the core is clogged or you still have a substantial air bubble in the heater core.

[Avant1.8BT]

At the next cold start don't let your car idle for that long. Give it 1 minute to warm up and then drive it gently. It should reach full temperature in no more than 5 minutes. However, if your temperature gauge is eventually getting the the 12:00 position you should then have heat. If the engine is at temperature but you don't have heat and the heater core supply/return hoses are still cold either the core is clogged or you still have a substantial air bubble in the heater core.

one minute warm up and dive, the car will take longer then 5 minutes to reach noon, is there another issue I need to address?

I have flushed out the supply hoses and last time I flushed the core. ( I have done that twice).

Proper cooling system bleeding thread I am missing?

[old guy]

If the thermostat is functioning properly it should not take more than 5 minutes to reach full operating temperature. But that's a separate issue from your lack of heat.

Have you bled the heater core from the return line bleeder hole? If you pull back slowly on the upper hose the air will be released from the bleeder hole. As soon as coolant starts to flow push the hose back in place.

[Waspjr]

Yes old guy is again passing on great info our 1.8t can be a real bear to properly bleed i prop my rez up as high as i can to try and get as much head pressure as i can. Be very very careful on those lines if you pry and pull you can easily give yourself a good 10 hr visit in your garage changing a heater core


Sent from my iPhone using Tapatalk

[Avant1.8BT]

If the thermostat is functioning properly it should not take more than 5 minutes to reach full operating temperature. But that's a separate issue from your lack of heat.

Have you bled the heater core from the return line bleeder hole? If you pull back slowly on the upper hose the air will be released from the bleeder hole. As soon as coolant starts to flow push the hose back in place.

Thank you for all the help old guy.


Just went on a ride, car took 11 minutes to heat up.

Came back to the shop opened the hood and cracked the return line. I few small bubbles came out then straight water, cold water.




The bottom hose, assuming thats the "in" was warm to touch as well.



if any of this helps...

[Waspjr]

I would repeat this a couple of times build press then perg


Sent from my iPhone using Tapatalk

[old guy]

I am having trouble reading the temperature gauge in your pics. Is that 68° c on the upper return hard pipe?

Are your radiator fans running on start up?

[Avant1.8BT]

All temperatures are in fahrenheit.

- - - Updated - - -

I am having trouble reading the temperature gauge in your pics. Is that 68° c on the upper return hard pipe?

Are your radiator fans running on start up?

Will check with radiator fans, I do not believe so.

[old guy]

Are you sure that gauge is working correctly? Can you hold your hand on the upper return hard pipe after driving the car?

[Avant1.8BT]

its read 168*** I am sorry, so no i can not, its hot.

[Avant1.8BT]

[old guy]

its read 168*** I am sorry, so no i can not, its hot.

OK. That makes a lot more sense. It looked like 68 in the pic so I assumed it may be in °c.

If the engine is up to full operating temperature the upper hard pipe at idle should be closer to 200°f. It sounds like you need a new thermostat for starters. The temperature gauge in the display reaches the 12:00 position at 175°f and doesn't go past straight up until over 230°

If the fans are running at start up that would be an indication that the ECM notices a discrepancy in the expected temperature readings between the two coolant temperature sensors. When this happens the fans run on high and the ECM turns on the thermostat heater to force the thermostat open. This can prevent your engine from reaching full operating temperature.

The other, and most likely scenario is that you need a new thermostat. Do you have the capability to monitor your ECM? Vagcom or VCDS?

EDIT: Got called to dinner. Back in about 20 minutes.

[Avant1.8BT]

OK. That makes a lot more sense. It looked like 68 in the pic so I assumed it may be in °c.

If the engine is up to full operating temperature the upper hard pipe at idle should be closer to 200°f. It sounds like you need a new thermostat for starters. The temperature gauge in the display reaches the 12:00 position at 175°f and doesn't go past straight up until over 230°

If the fans are running at start up that would be an indication that the ECM notices a discrepancy in the expected temperature readings between the two coolant temperature sensors. When this happens the fans run on high and the ECM turns on the thermostat heater to force the thermostat open. This can prevent your engine from reaching full operating temperature.

The other, and most likely scenario is that you need a new thermostat. Do you have the capability to monitor your ECM? Vagcom or VCDS?

EDIT: Got called to dinner. Back in about 20 minutes.

Well I just took the car on a drive from hell. I think I might be getting somewhere.

The upper hose


The lower hose

[old guy]

What is the upper return hard pipe reading?

[Avant1.8BT]

What is the upper return hard pipe reading?

it rose from 168.. to 187... I did not take a picture. So it did not reach 200 like it should have.

[old guy]

it rose from 168.. to 187... I did not take a picture. So it did not reach 200 like it should have.

That sounds like you may need a new thermostat. Plus you still have an issue with the heater core circulation. As Waspjr pointed out you may need to bleed it several times to purge all of the air.

To completely rule out the ECM affecting the thermostat you need to pull codes and/or monitor the CTS activity. If you don't have the equipment to do this there is one quick check that you can do to confirm the thermostat is functioning properly. Simply unplug the thermostat heater and monitor the upper return hard pipe. If the temperature stays essentially the same the issue is with the thermostat. If the temperature climbs to 200+°F you have a problem with one of your CTS's.

This action may give you a CEL but that will be easy to deal with once you confirm the thermostat activity.

[Avant1.8BT]

That sounds like you may need a new thermostat. Plus you still have an issue with the heater core circulation. As Waspjr pointed out you may need to bleed it several times to purge all of the air.

To completely rule out the ECM affecting the thermostat you need to pull codes and/or monitor the CTS activity. If you don't have the equipment to do this there is one quick check that you can do to confirm the thermostat is functioning properly. Simply unplug the thermostat heater and monitor the upper return hard pipe. If the temperature stays essentially the same the issue is with the thermostat. If the temperature climbs to 200+°F you have a problem with one of your CTS's.

This action may give you a CEL but that will be easy to deal with once you confirm the thermostat activity.

I let her cool back down, fired her back up. The fans are both on, blowing hard. So, looks like i need to replace both of the coolant temperature sensors. Besides the temp sensors reading different, would something else cause the fans to fire up right away?

[old guy]

The fans coming on at start up occurs when the ECM is getting conflicting information from the two sensors. It knows something is wrong but it doesn't know exactly what so it goes into a protection mode which includes applying full power to the thermostat heater as well as running the fans on high to provide maximum cooling to the engine.

Without being able to monitor the measuring blocks to see what is really going on all you can do is guess. It could be a faulty CTS or it could be because of a faulty thermostat. That is why I suggested unplugging the heater to the thermostat to see if it changes the block temperature. If the block heats up normally without the heater plugged in that would indicate a faulty CTS causing the problem. If the block temperature stays lower than normal that would indicate a faulty thermostat.

Edit: I should also mention that if you check for codes you will find one for the cooling system malfunction. Your engine will remain in this condition until the code is reset (fans on high at start up, full power to the thermostat heater).

[Protection]

I have struggled in the past with bleeding my 1.8t B6. I purchased an 'Airlift' vacuum coolant tool to refill the system and have still had issues with air pockets. There is an easy way to determine if you have an air bubble in the system. When your engine is cold note your coolant level. Drive your car around until it is at operating temp. Then pop the hood and note the coolant level. If it is low, GRADUALLY, open the coolant reservoir cap, just till it releases pressure-then quickly tighten it to keep hot coolant from spraying everywhere and burning you. If the reservoir was low, but after releasing pressure the coolant all comes rushing back into the reservoir, you have air trapped in the system. Since air compresses under pressure, unlike coolant, the reserve coolant in the reservoir will be drawn out as the engine gets hot and the air pocket in the system compresses. When you depressurize the system by opening the reservoir cap, the air pocket rapidly expands causing the coolant to be pushed back into the reservoir.

It sounds like you may have other issues going on, but I'm fairly confident based on the heater core hose temps, you have air trapped in the system.


Sent from my iPhone using Tapatalk

[Avant1.8BT]

The fans coming on at start up occurs when the ECM is getting conflicting information from the two sensors. It knows something is wrong but it doesn't know exactly what so it goes into a protection mode which includes applying full power to the thermostat heater as well as running the fans on high to provide maximum cooling to the engine.

Without being able to monitor the measuring blocks to see what is really going on all you can do is guess. It could be a faulty CTS or it could be because of a faulty thermostat. That is why I suggested unplugging the heater to the thermostat to see if it changes the block temperature. If the block heats up normally without the heater plugged in that would indicate a faulty CTS causing the problem. If the block temperature stays lower than normal that would indicate a faulty thermostat.

Edit: I should also mention that if you check for codes you will find one for the cooling system malfunction. Your engine will remain in this condition until the code is reset (fans on high at start up, full power to the thermostat heater).

Okay, Update:

I replaced, the coolant flange on the back of the head, it had a slight leak.

I replaced both coolant temp sensors, 2 pin and 4 pin.

I replaced the coolant expansion tank, the lid wasn't a good fit/warped.

I started the car up, no fans, it still took a while to warm up but MUCH quicker. I bleed air/steam 2-4 times then couldn't get anything but water to come out.

The hard pipe reach a temp of 196 degrees.

The return hose on the heater core reached 90 degrees, inlet still reaching 130-140 degrees.


When driving the car, the heat was warm, when slowing to a stop it would cool down.


I pulled the return hose off completely at one point, had my mate rev the engine and water came out the core, didn't explode, but ran out quick.

Why can't I get water to push through my heater core!

[Protection]

You're not getting water through the core because you have an air lock. You can pull the hose off the heater core and have coolant spray out of that tiny hole all day without getting the trapped air out. If there is a foolproof method, I haven't found it yet.
I built my own little gizmo from parts I got at Home Despot. Allows me to use a bicycle pump to pressurize the system while cold and bleed it then. See picture below. I found what worked for me, once I had bled the system enough to have luke warm heat while idling and hot while driving, was to simply 'burb' the expansion tank three or four times.
I would drive the car to the store or wherever, and when I got home I would slowly open the cap on the expansion tank till it pops, releasing pressure, than quickly tighten it up before coolant came spraying out. When the pressure is released, coolant and bubbles would come rushing into the expansion tank. After doing this three times over several days, I had broiling hot heat. My troubles began after I drained the coolant to replace the timing belt.





Sent from my iPhone using Tapatalk

[Avant1.8BT]

When you pressurize the cooling system, where did you bleed it from?

[old guy]

You probably still have some air in the heater core. Pulling the hose off completely actually makes the situation worse. The coolant has multiple paths to get from the water pump to the radiator. When the coolant exits the block through the rear coolant flange it can either exit through the upper hard pipe or the heater core supply line.

To get flow through the heater core the coolant exits the rear flange, travels down the supply line and then up to the hard pipe supplying the core. It then flows from the bottom of the core to the top of the core where it exits and then flows down to the lower return hard pipe and ultimately to the thermostat housing.

In order to get proper flow through the core it is critical that there is an uninterrupted column of coolant. There are two forces required to get flow through the core. There is the "push" of coolant that exits through the rear coolant flange. But just as important is the "pull" or suction of coolant as the water pump pulls coolant through the thermostat housing and pumps it into the block.

If there is any air in the core it breaks the column of coolant. Picture in your mind a siphon tube. Once there is an air break in the siphon tube the liquid can no longer be pulled through the tube. This is exactly what happens when you have air in the heater core. At idle there is no suction force to pull coolant through the core and consequently all of the coolant return goes through the upper return hard pipe.

Once you start driving the "push" from the water pump increases enough to push some coolant through heater core. As you slow the engine down the push is no longer strong enough and without the "pull" from the exit end of the core the circulation stops and the heat goes cold.

Sometimes it takes multiple bleedings to get all the air out. Once you understand the dynamics of how it functions you can see where pulling the hose completely off will only create more of an issue.

Good luck!

[Avant1.8BT]

So, continue bleeding the car from the upper hose for the next few days.

I have been keeping the car at idle when I slide back the hose to the breather port, this is correct right?

Old guy, have you ever tried the pressurizing system method? I have only used that method to find leaks never to bleed air out.



Thanks again for all the input and information.

[old guy]

I have the best luck by raising the reservoir tank to increase the head pressure and very slowly add coolant. Once it starts running out of the bleeder hole I push the hose back in place.

[Avant1.8BT]

Car off?

[Protection]

That was a very concise explanation Old Guy, bravo.

Like you Avant1.8BT, I too bled through that little hole on the heater core exit pipe and also the tap on the hard pipe. But my point was, that doing that alone is not sufficient. I didn't get hot heat till I burped the reservoir several times. Based upon your previous post, since you have luke warm heat, I would try and drive the car then burp the coolant tank several times before heading off to the nearest HD to fabricate a pressure tool.

If you opt to make the tool, it is hard to get the bottom clamp sufficiently around the coolant reservoir cap fitting to hold more than 10psi. Therefore, do not put more than 10 psi of pressure into the reservoir, or you risk creating an air rocket from your pressure tool.


Sent from my iPhone using Tapatalk

[old guy]

Car off?

Yes. Off and cold. I've also done it hot and under pressure from the bleed hole if I don't get it the first time doing it cold. Multiple small burps.

[Avant1.8BT]

Yes. Off and cold. I've also done it hot and under pressure from the bleed hole if I don't get it the first time doing it cold. Multiple small burps.

Okay, and If I am getting water to come out... do i let it spray out for a minute or two? or pull the hose over. wait and repeat?

[DiertyEuroSpec]

I dont see how people have such a hard time with these cooling systems?? If in fact it takes all that effort I suggest the coolant filler ECS sells. I have never had an issue and I just recently swapped motors so you know my system was practically bone dry.

All I do is leave coolant tank unsecured fill coolant tank with tapped bleeder open, raise tank and keep filling until coolant exits hard pipe bleeder. Thats it. Then drive it top it up and next day heat is normal. I pressume anyone who has difficulties has issues somewhere in the system where it be deposits begining to clog or something else.

Sent from my LGL33L using Tapatalk

[Protection]

I have tried your method without success. I only wish it was so easy for mine. I don't know why some cars are more difficult than others. I have a B5 S4 that is never a problem (thank goodness because It seems that removing the engine is an annual event).

What ECS tool are you referring to? Their version of the Airlift evacuator? If so, I have used that as well w/o success.


Sent from my iPhone using Tapatalk

[yousifa4]

Check your coolant flange, you might have leak there

thats where it is located, right behind the engine



and this is how it looks:

[DiertyEuroSpec]

Yea it was the Airlift made by Schwben I think, and if that didn't even work then I dont really have any answer. Maybe you need to look into areas that are letting air in.

Sent from my LGL33L using Tapatalk

[old guy]

Since I'm kinda lazy and don't feel like doing a lot of typing tonight I figured I would add a copy/paste from a previous thread where I described how the 1.8T cooling system functions. Knowing how it functions helps in troubleshooting cooling and heating issues:

Here's how the cooling system works. The thermostat housing does more than just contain the t-stat. The housing determines the directional flow of coolant. Depending upon the coolant temperature the coolant either flows through the small loop or the large loop.

SMALL LOOP: When you first start a cold motor the water pump sucks coolant through the t-stat housing. The t-stat will be in a closed position so the coolant gets sucked from the block side of the housing which gets coolant from numerous sources other than the radiator (Which is part of the large loop). The water pump pushes the coolant through the block. It then exits through the rear coolant flange and flows in two directions.

One split goes to the heater core supply hose. That line supplies coolant to the heater core. When it leaves the heater core it connects to the lower coolant return hard pipe. The lower coolant return hard pipe connects back to the thermostat housing on the block side of the t-stat housing. The coolant flows across the actuating side of the t-stat.

The other split supplies coolant to the upper coolant return hard pipe. The upper coolant return hard pipe connects to the top of the radiator. However, as long as the t-stat is closed the coolant cannot flow down through the radiator. There are two drops off of the upper coolant return hard pipe that are always open. One of the drops supplies the oil cooler. The coolant flows through the oil cooler and then returns through the lower coolant return hard pipe. The other drop goes directly to the t-stat housing on the block side of the t-stat.

LARGE LOOP: Once the coolant temperature flowing through the block side of the t-stat housing (from the lower coolant return hard pipe and coolant drop from the upper coolant return hard pipe) gets hot enough the t-stat opens. When the t-stat opens coolant will start to flow through the radiator from the upper return hard pipe and exiting into the t-stat via lower radiator return hose. Coolant will continue to flow through the radiator until the temperature drops below the t-stat opening temperature. When that happens the coolant flow will return to the small loop as described above.



Keep these functions in mind as you reread post #26. Hopefully it will help you visualize exactly what is going on when you go to bleed the cooling system.

[egovreau]

You're not getting water through the core because you have an air lock. You can pull the hose off the heater core and have coolant spray out of that tiny hole all day without getting the trapped air out. If there is a foolproof method, I haven't found it yet.
I built my own little gizmo from parts I got at Home Despot. Allows me to use a bicycle pump to pressurize the system while cold and bleed it then. See picture below. I found what worked for me, once I had bled the system enough to have luke warm heat while idling and hot while driving, was to simply 'burb' the expansion tank three or four times.
I would drive the car to the store or wherever, and when I got home I would slowly open the cap on the expansion tank till it pops, releasing pressure, than quickly tighten it up before coolant came spraying out. When the pressure is released, coolant and bubbles would come rushing into the expansion tank. After doing this three times over several days, I had broiling hot heat. My troubles began after I drained the coolant to replace the timing belt.





Sent from my iPhone using Tapatalk

I have the old reservoir cap I replaced that I might look into modifying to pressurize the system. It was functional when I replaced it...just decided the replace the cap when I put a new tank in. Nothing ventured, nothing gained.

[BARRY]

you need to back fill and forward fill your cooling system. it seems you have many air pockets throughout your cooling system

if your thermostat doesn't have coolant on the inward side and none on the out going side it will not be able to direct flow appropriately to purge the air out of your system. this does by always happen but you'll have to try to add coolant at the highest point of the cooling system as well as the expansion tank. at the heater core as well as the upper hard pipe going across the intake manifold.

[eljay]

This is a very useful thread as I'm about refill my coolant after a rear flange replacement. I lost 2L of coolant during the process. So, from all of the above, I gather that the best way to refill the coolant would be to raise the coolant reservoir a little to make it the highest point in the system, release the bleeder screw on the hard pipe and add coolant to the reservoir until I see coolant coming out of the bleeder screw, close the screw, put the reservoir back, go for a drive, and slowly purge from the reservoir cap after the drive, then refill the coolant to the appropriate level. Is that it?
I had good heat in the car before, so if I manage to add 2L back to the system to get me to the level I was before, I should be confident of no air pockets, right?