04 1.8t Air in Cooling system

[davidm2232]

I'm having some serious airlock issues on my B6. About a month ago, I started having issues with no heat at idle or low rpms. I checked the coolant level and it was good. I drove it for a couple weeks and it got progressively worse, where I would have to rev the engine first to 2500 rpm and then 3000 rpm to get heat. I bled air out of the Allen bolt hole and the heater core bleeder. Heat was good at idle and while driving for the first day. The next day it was back to no heat below 2500 rpms. I unscrewed the coolant bottle and lifted it up with a bungee cord to the hood. Ran the engine at idle and bled some air out the bleeder screw. I took the lid off the bottle and then let the car run. I got a few small bubbles. I had great heat at idle at this point. I then revved the car to about 5000 rpms for 15 seconds. There were no bubbles. When I let it go back to idle, huge amounts of bubbles came out. I still had great heat. That was last night. This morning, I drove to work and had better heat but still nothing at idle. Also, the car will randomly go almost all the way cold and then back to normal within a minute or so and will go almost all the way hot for about 30 seconds before going back to normal. I did a 0-110 mph run at wide open to see if i could get it to overheat. Temp stayed right at the middle through the whole run and then went all the way cold for a few minutes before coming back to normal. I know I am getting air in the system but I cannot figure out where or how. There was a small leak where a rubber hose goes into the top metal pipe that I fixed. I do not think head-gasket as it doesn't overheat under load. I am out of ideas. Any help would be appreciated.

[eljay]

I'm having some serious airlock issues on my B6. About a month ago, I started having issues with no heat at idle or low rpms. I checked the coolant level and it was good. I drove it for a couple weeks and it got progressively worse, where I would have to rev the engine first to 2500 rpm and then 3000 rpm to get heat. I bled air out of the Allen bolt hole and the heater core bleeder. Heat was good at idle and while driving for the first day. The next day it was back to no heat below 2500 rpms. I unscrewed the coolant bottle and lifted it up with a bungee cord to the hood. Ran the engine at idle and bled some air out the bleeder screw. I took the lid off the bottle and then let the car run. I got a few small bubbles. I had great heat at idle at this point. I then revved the car to about 5000 rpms for 15 seconds. There were no bubbles. When I let it go back to idle, huge amounts of bubbles came out. I still had great heat. That was last night. This morning, I drove to work and had better heat but still nothing at idle. Also, the car will randomly go almost all the way cold and then back to normal within a minute or so and will go almost all the way hot for about 30 seconds before going back to normal. I did a 0-110 mph run at wide open to see if i could get it to overheat. Temp stayed right at the middle through the whole run and then went all the way cold for a few minutes before coming back to normal. I know I am getting air in the system but I cannot figure out where or how. There was a small leak where a rubber hose goes into the top metal pipe that I fixed. I do not think head-gasket as it doesn't overheat under load. I am out of ideas. Any help would be appreciated.

I just bled my system last night after refilling about 2.5L of coolant. You can read my Q&A in this thread to give you more detail: http://www.audizine.com/forum/showth...e-an-easy-one!
I bolded your statement up above since it implies that when you lifted the reservoir high, you only used the bleeder screw on the hardline, but this time you did not bleed the heater core hose. You must also bleed the heater core hose. With the reservoir high, open both again, bleed hardline and then bleed the heater core hose after.

[davidm2232]

I have bled both from the bleeder screw and the heater core a few times. The issue goes away and I get heat for a few hours and then it goes back to being airlocked. I need to find out where the air is coming from. I just ordered a thermostat, housing, and jplug and will try those. Does that sound like a good next step?

[BARRY]

rear coolant outlet pipe as well.

[old guy]

I'm having some serious airlock issues on my B6. About a month ago, I started having issues with no heat at idle or low rpms. I checked the coolant level and it was good. I drove it for a couple weeks and it got progressively worse, where I would have to rev the engine first to 2500 rpm and then 3000 rpm to get heat. I bled air out of the Allen bolt hole and the heater core bleeder. Heat was good at idle and while driving for the first day. The next day it was back to no heat below 2500 rpms. I unscrewed the coolant bottle and lifted it up with a bungee cord to the hood. Ran the engine at idle and bled some air out the bleeder screw. I took the lid off the bottle and then let the car run. I got a few small bubbles. I had great heat at idle at this point. I then revved the car to about 5000 rpms for 15 seconds. There were no bubbles. When I let it go back to idle, huge amounts of bubbles came out. I still had great heat.

This indicates that your heater core is functioning properly and isn't partially clogged.

That was last night. This morning, I drove to work and had better heat but still nothing at idle. Also, the car will randomly go almost all the way cold and then back to normal within a minute or so and will go almost all the way hot for about 30 seconds before going back to normal. I did a 0-110 mph run at wide open to see if i could get it to overheat. Temp stayed right at the middle through the whole run and then went all the way cold for a few minutes before coming back to normal.

This could be caused by several different things. It could be thermostat related or it could be coming from an air pocket passing by the rear CTS. Do you have the ability to monitor measuring blocks? That could really help to quickly narrow it down.

I know I am getting air in the system but I cannot figure out where or how.There was a small leak where a rubber hose goes into the top metal pipe that I fixed. I do not think head-gasket as it doesn't overheat under load. I am out of ideas. Any help would be appreciated.

A deteriorating "J" plug can cause some some tough to figure out issues with the cooling system.


The plug tends to degenerate from the inside. What happens is that it will hold pressure from the inside so there is no outward indication of a leak. But once the block completely cools down the coolant volume reduces and air gets pulled in through the defective "J" plug. This introduces air pockets into the cooling system and then you begin to have issues with temperature control and heater core functionality.

[crazyquik22023]

The plug tends to degenerate from the inside. What happens is that it will hold pressure from the inside so there is no outward indication of a leak. But once the block completely cools down the coolant volume reduces and air gets pulled in through the defective "J" plug. This introduces air pockets into the cooling system and then you begin to have issues with temperature control and heater core functionality.

If you do find your j plug to be broken off like this make sure to check your water pump impeller as well when you have the thermostat off. If the j plug is broken then the piece that broke off more than likely would have damaged the pump.

[refueler]

I had a similar problem only got heat at higher rpm's tried all of the suggested methods of bleeding air from the cooling system even bought a vacuum fill system which I use to fill all cooling systems now. Every time I would bled air from the cooling system there was always air in the system it was a never ending supply of air. I did compression tests, cylinder leak down tests, had the heater core pulsed pressure back flushed, replaced the J plug and thermostat sent the cylinder head to a machine shop had it pressure tested, machined flat, installed a new head gasket. Still had the same problem so I took the head back off again and sent back to the machine shop had them perform a dye penetration test to look for cracks they found 6 cracks in and around cylinders #2 and # 3. I bought another head and installed it with a new head gasket problem solved. Don't know why the cylinder head pressure test passed. I come out of the nuclear world and when you are looking to verify that there are no cracks you perform pt's not hydro's. That's my story I hope yours ends better.

[Europotvin]

I had a similar problem only got heat at higher rpm's tried all of the suggested methods of bleeding air from the cooling system even bought a vacuum fill system which I use to fill all cooling systems now. Every time I would bled air from the cooling system there was always air in the system it was a never ending supply of air. I did compression tests, cylinder leak down tests, had the heater core pulsed pressure back flushed, replaced the J plug and thermostat sent the cylinder head to a machine shop had it pressure tested, machined flat, installed a new head gasket. Still had the same problem so I took the head back off again and sent back to the machine shop had them perform a dye penetration test to look for cracks they found 6 cracks in and around cylinders #2 and # 3. I bought another head and installed it with a new head gasket problem solved. Don't know why the cylinder head pressure test passed. I come out of the nuclear world and when you are looking to verify that there are no cracks you perform pt's not hydro's. That's my story I hope yours ends better.

Ouch ... I went thru the exact same steps as you (changed all cooling system parts) and still don't seem to be able to get proper heat. I also tried filling up my coolant with a vaccum tool but no luck. Did you have any other symptoms except air in the coolant ? (over heating, coolant consumption). I really hope its not my head ...

[refueler]

Yes I did experience very small amounts of coolant loss, at first it was about 1 cup or so per month and it did over time increase to about 1 cup per week. I continued to drive the car because it wasn't overheating or so I thought. The cooking system has two cooling loops in the small loop coolant is always flowing through the motor from the water pump out the rear coolant flange where it can go in one of two ways through the heater core and the metal distribution pipe the large loop comes into play when additional cooling is required the thermostat opens allowing coolant to flow through the radiator. The presence of the air bubble in the coolant flange / heater core makes it difficult to circulate coolant through the metal distribution pipe on top of the motor and the heater core at lower rpm's. My theory is that the engine over heats but the temperature gauge doesn't indicate it. The air or combustion gas accumulate in the high point in the system which is the rear coolant flange/heater core and the sensor doesn't indicate that the engine is overheating because the sensor is in air instead of coolant. Because the air bubble disrupts the flow of coolant into the heater core/motor at lower rpm you get no heat at higher rpms coolant pump can get the coolant to flow through the motor and the heater core giving heat. If you catch it when the coolant first starts flowing through the motor/ heater core the temperature does go up. Have you felt the hoses that go to the radiator the top hose is very hot and the lower hose will be cold. The cooling system has two cooling loops the small loop doesn't send coolant to the radiator until additional cooling is required which I think that information is input via the sensor in the rear coolant flange and it is in air not coolant and it doesn't register the correct temperature. This is how I think the cooling system works when air is trapped in the cooling system.

[diagnosticator]

I had a similar problem only got heat at higher rpm's tried all of the suggested methods of bleeding air from the cooling system even bought a vacuum fill system which I use to fill all cooling systems now. Every time I would bled air from the cooling system there was always air in the system it was a never ending supply of air. I did compression tests, cylinder leak down tests, had the heater core pulsed pressure back flushed, replaced the J plug and thermostat sent the cylinder head to a machine shop had it pressure tested, machined flat, installed a new head gasket. Still had the same problem so I took the head back off again and sent back to the machine shop had them perform a dye penetration test to look for cracks they found 6 cracks in and around cylinders #2 and # 3. I bought another head and installed it with a new head gasket problem solved. Don't know why the cylinder head pressure test passed. I come out of the nuclear world and when you are looking to verify that there are no cracks you perform pt's not hydro's. That's my story I hope yours ends better.

The fact with cracks that develop between the valve seats, is that those cracks cannot in any way leak coolant into the cylinders or air into the cooling system because there is no coolant jackets anywhere near the areas between the valve seats. This is why thermal stress cracks develop between the valve seats to begin with. Audi allows cracks between the valve seats as long as they are less than ~ 1mm wide. It is more likely the head gasket had failed and replacing the head automatically fixed the problem, or the cracks were located in a different place allowing air to get into the cooling system when the engine cooled down.

[davidm2232]

Ok, on Saturday, I replaced the thermostat and housing as well as the Jplug. I'm glad I did as the Jplug was pretty disintegrated. I put everything back together and started to bleed the system. I kept getting crazy amounts of air/steam out the bleeder screw and it would bubble out the expansion tank unless i kept the lid closed. I bled it for over an hour and it did get better. I would get coolant only and no pressure in the bottle until the thermostat opened. Then, big stream of bubbles and pressure until the tstat closed and then it would be fine again. At that point, the heat was so hot I couldn't hold my hand over the vent. I took it for a test drive and had no issues. Heat was so hot I had the window down comfortably in 30 deg. temps. I shut the car off and later that night took it on a 90 mile trip. Car was back to having problems again. Random no heat, random overheat, and coolant running out the overflow. On my way home, the temp gauge shot up a few times then right back down. Seems like lots of air still. I got back on Sunday and bled the system again. Still was getting lot's of air only when the tstat is open. I have been driving the car since and have found a predictable pattern. At cold start, there is no heat. I drive until the thermostat opens. Brief overheat and then good warm air out the heater. Then it goes cold again. Once the tstat opens a second time, water temp gauge shoots up again and back down and I have heat again. I have decent/intermittent heat for the next 20 miles and minimal movement on the gauge. A couple people have said head gasket but I'm still not convinced. Why only bubbles when the tstat opens? Is it possible I'm getting air in from the Rad or rad hoses somehow? Is there an oring on the lower rad hose that connects to the tstat housing? Maybe I should replace that. Anyone have a part number?

[crazyquik22023]

Is there an oring on the lower rad hose that connects to the tstat housing? Maybe I should replace that. Anyone have a part number?

You are definitely sucking in air from somewhere. There is an o-ring on the lower radiator hose that connects to the thermostat housing, but it rarely needs replaced. I'm pretty sure there is no part # for it in ETKA. Did you replace the o-ring on the water pipe that goes into the thermostat housing? Part # WHT006407.

[davidm2232]

I was just looking at new coolant bottle caps. Looks like they are rated at 22psi. Mine opens around 15 psi when I did a pressure test on the system. Could that be part of my problem?

[customa4]

You are definitely sucking in air from somewhere. There is an o-ring on the lower radiator hose that connects to the thermostat housing, but it rarely needs replaced. I'm pretty sure there is no part # for it in ETKA. Did you replace the o-ring on the water pipe that goes into the thermostat housing? Part # WHT006407.

That would be a good idea to replace the o-ring crazyquik mentioned. When I was in there mine seemed pretty flattened and not much of an o-ring anymore.

[davidm2232]

Yep, that oring came in the kit so I replaced it. I'm thinking radiator/rad lines somewhere as you can definitely tell it is giving bubbles only when the tstat opens. I've got a coolant pressure tester adapter on order so maybe that will help me narrow down the issue.

[crazyquik22023]

Unless I missed it somewhere I didn't read that you bled at the heater core after replacing the thermostat. The heater core hoses are the highest point in the system so if there is air trapped there you need to bleed it from the nipple on the heater core hose. Even if you bleed it from the bleeder screw on the water pipe there could still be air trapped in the hoses above that screw.

[davidm2232]

Unless I missed it somewhere I didn't read that you bled at the heater core after replacing the thermostat. The heater core hoses are the highest point in the system so if there is air trapped there you need to bleed it from the nipple on the heater core hose. Even if you bleed it from the bleeder screw on the water pipe there could still be air trapped in the hoses above that screw.

Yep, bled from heater hoses also. It seems I can get all/most of the air out but it comes back eventually.

[SJorge3442]

You can always tell when the temps are dropping because so many of you 1.8 guys have issues getting the air out. What about one of these? I know if I had issues with air in the system, this would be the first tool I'd turn to. Less than 1 hour's work at most shops and you can use it forever.

[davidm2232]

You can always tell when the temps are dropping because so many of you 1.8 guys have issues getting the air out. What about one of these? I know if I had issues with air in the system, this would be the first tool I'd turn to. Less than 1 hour's work at most shops and you can use it forever.

I think my buddy has that tool. I'm going to use it when I fill my system for the last time. My issue is trying to figure out where the air is coming from. I don't want to waste another gallon of coolant if I can't figure out why it's going out the bottle

[customa4]

You should make sure there's not a problem with the coolant cap/tank.

[davidm2232]

You should make sure there's not a problem with the coolant cap/tank.

Well, this whole issue started a couple weeks after I put a new coolant bottle on. The old one was cracked and leaking for almost a year. I think my next step is going to be a new cap as mine is venting at around 12-15 psi rather than 22.

[SJorge3442]

Well, this whole issue started a couple weeks after I put a new coolant bottle on. The old one was cracked and leaking for almost a year. I think my next step is going to be a new cap as mine is venting at around 12-15 psi rather than 22.

A leaky cap would cause the system to not be able to build pressure, thus allowing the coolant to get to much higher temperature levels, which could be causing the over-heat issue, but someone chime in here. If a cap is not holding pressure, wouldn't this help to vent the system and get the air out by itself? BUUUUUT, if the system sucks the tank dry when it hiccups or burps, you could suck air in.

So many ways to go from here, but I'd say get a coolant cap and go from there.

[davidm2232]

A leaky cap would cause the system to not be able to build pressure, thus allowing the coolant to get to much higher temperature levels, which could be causing the over-heat issue, but someone chime in here. If a cap is not holding pressure, wouldn't this help to vent the system and get the air out by itself? BUUUUUT, if the system sucks the tank dry when it hiccups or burps, you could suck air in.

So many ways to go from here, but I'd say get a coolant cap and go from there.

That's what I'm thinking. If I can keep the coolant in there, I should have less problems.

[customa4]

And go OEM! Don't waste your money buying aftermarket crap. Plenty of people have had problems with aftermarket tanks(including me) and caps. Give yourself peace of mind and buy OEM parts. Just find them online for discounted prices. Yes, it may cost you $60-$70 but it's better than spending $40 to find out it's crap. I did the same thing at the beginning of my Audi ownership and bought cheap aftermarket parts only to go back and replace it with OEM. Only thing I buy aftermarket now is upgraded parts(suspension, intercooler, exhaust...).

[davidm2232]

And go OEM! Don't waste your money buying aftermarket crap. Plenty of people have had problems with aftermarket tanks(including me) and caps. Give yourself peace of mind and buy OEM parts. Just find them online for discounted prices. Yes, it may cost you $60-$70 but it's better than spending $40 to find out it's crap. I did the same thing at the beginning of my Audi ownership and bought cheap aftermarket parts only to go back and replace it with OEM. Only thing I buy aftermarket now is upgraded parts(suspension, intercooler, exhaust...).

I can get an aftermarket cap for $8 locally so I'll try that. The problem with getting OEM stuff is the closest dealer is an hour away so when you need stuff immediately, it's usually Advance Auto or nothing.

[old guy]

I was just looking at new coolant bottle caps. Looks like they are rated at 22psi. Mine opens around 15 psi when I did a pressure test on the system. Could that be part of my problem?

Could be. The OEM cap is rated for 1.5 bar. Several years ago I replaced my OEM cap with a new one (not OEM) and noticed I was blowing off coolant. I pressure tested the cap and found the same thing that you did. It was blowing off at 1 bar. Put the OEM one back on and it cured the problem.

[davidm2232]

Good news and bad news. I pulled the car in the garage Friday night to check for a headgasket leak. I borrowed the exhaust gas testing tool but didn't even need it. I could smell exhaust in the coolant bottle easily. We decided to pull the head and check for any leaks. After getting it off, head and gasket looked fine. Head was slightly uneven when straight edge was put on it so we put a spare head on with new gasket and bolts. Drove the car and I had heat!! I have driven it a few times and no issues. I will need to get a new valve cover gasket though, leaks a good amount of oil. The only issue now is that the replacement head did not have variable cam timing. I don't want to swap my old tensioner on as it was worn and setting codes as it was. I want to just tune out vvt and sai from the ecu. I am pretty good tuning the alh's but I'm not familiar with these. I raed through this: http://s4wiki.com/wiki/Tuning but am still unsure what I need to do. I have two ESKONF tables, one with 91 and one with 93. Any ideas what to set them on to tune vvt and sai out? All in all, happy I got it going again. Now just to get rid of the damn Cel...

[BARRY]

glad you figured it out...as much as many state chinese made vvt tensioners are bad...the one i've installed from ebay runs fine...if it goes bad and i need to swap it out it isn't that difficult to do either. if you're paying someone then go OEM or OEM brand.