2004 a4 1.8t no heat??Heater core replaced,Timing belt,water pump,thermostat.Anyone?

[EuroxS4]

So I replaced the timing belt,water pump, thermostat,coolant temp switch,j plug about a week ago.All oem parts.Vacuum bled cooling system without issues.I replaced the heater core today.Still the same thing.I tried another climate control head performed basic settings no change.When driven at highway speeds under load vehicle has some hear but not a whole lot.There is no air in the system because I bled the heater core at the return hose with the hole in it.I am wondering if the radiator could be restricted??or partially blocked??Never had any issues.About 2 weeks ago the car would over heat in the morning when started and a key cycle would fix this.I found out that the coolant temp sensor on the rear of the head was no good and causing this so that was replaced.As mentioned just about everything was replaced beside radiator and lower temp switch on the lower radiator hose.Any chance this switch is my issue or the radiator is partially blocked???No faults stored in HVAC 08 or engine 01.Really weird.

[tHatOne guY]

I would check the air mix and blend door servo linkages just the verify they are indeed moving, I know you said you scanned for codes and performed basic settings though.

If that didn't pan out then maybe a radiator flush is in order. An infrared thermometer is helpful determining a blockage in the radiator by significant temp differences from upper to lower tanks.

That lower switch controls the fan activation, so if the engine does not get to normal operating temp then they won't come on. Sure you can monitor it's values in VCDS.

[EuroxS4]

Been there done that.I ran basic settings for all the flap motors,all came back working fine.Also replaced radiator thinking thats all that was left and the coolant temp switch on the lower hose.But I am still having the same issue.As it turns out the pump I had had a metal impeller which leads me to believe its not oem.I am wondering if that could be my issues as everything else was replaced???Also noticed today that when i started the car it idled fine for 30mins.I went to drive the ca it went to 3/4 on the temp gauge ans came back to normal and the heat came on but now its back to doing the same thing.I replaced the coolant tank and cap as well.It was ordered by vin so I would assume its right.But I am wondering if the tank cap is rated for a different pressure maybe???Only thing thats left would be a cracked head???or head gaskets??But if that was the case then It should be creating pressure inside the bottle and pushing coolant out out of the over flow???So I dont know but everything has been replaced and I still have the same problem.I've heard or head cracking on amb motors and gasket gaskets.But I would assume if i had a bad head gasket it would have cold start misfires or something??Also If i had a bad oil cooler I should see the coolant aka milkshake in the coolant bottle if that was the case.Not sure where to go with this.I might start by putting a oem pump in the car.Or maybe checking the coolant fan module???I havent touched that yet but I know the fans come on so I would assume its working fine.

[refueler]

I believe my problems started when I noticed that I was loosing about 1 cup of coolant a month. So I looked here for a solution which I found to be the rear coolant flange was leaking. After replacing the flange I didn't get air out of the system. I drove the car the temperature gauge never indicated that the engine was over heating it was summer time and I didn't check for heat. I learned my lesson I do not drive a car that the coolant was removed from until there is heat. I believe this caused the cracks in my amb head. My car always ran fine no misfires only got heat occasionally and usually going up hill under load . The upper coolant hoses were hot and were very firm as if under a lot of pressure, but the lower radiator hose was always cold. When the pressure was released by slowly opening the tank cap some bubbles would enter the expansion tank and the coolant level would rise in the tank. There was always air to bleed out of the metal distribution tube and the upper heater core bleed hole. I also replaced everything in the cooling system but the heater core and radiator. I decided that I had a bad head gasket sent it off to the machine shop for a pressure test and machining, don't know why but it passed the pressure test. I installed the head still had the same exact problem so I decided to take the head back off and sent it back to the machine shop and told them to perform a dye penetration test which revealed 6 cracks. I purchased a used head on e bay installed it with a new head gasket problem solved. This is my story I hope you solve your problem.

[jacobsen]

Been there done that.I ran basic settings for all the flap motors,all came back working fine.Also replaced radiator thinking thats all that was left and the coolant temp switch on the lower hose.But I am still having the same issue.As it turns out the pump I had had a metal impeller which leads me to believe its not oem.I am wondering if that could be my issues as everything else was replaced???Also noticed today that when i started the car it idled fine for 30mins.I went to drive the ca it went to 3/4 on the temp gauge ans came back to normal and the heat came on but now its back to doing the same thing.I replaced the coolant tank and cap as well.It was ordered by vin so I would assume its right.But I am wondering if the tank cap is rated for a different pressure maybe???Only thing thats left would be a cracked head???or head gaskets??But if that was the case then It should be creating pressure inside the bottle and pushing coolant out out of the over flow???So I dont know but everything has been replaced and I still have the same problem.I've heard or head cracking on amb motors and gasket gaskets.But I would assume if i had a bad head gasket it would have cold start misfires or something??Also If i had a bad oil cooler I should see the coolant aka milkshake in the coolant bottle if that was the case.Not sure where to go with this.I might start by putting a oem pump in the car.Or maybe checking the coolant fan module???I havent touched that yet but I know the fans come on so I would assume its working fine.

Are you sure there's no leak at the back of the head, check the coolant coupler on the hose to the heater core.

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[jacobsen]

I believe my problems started when I noticed that I was loosing about 1 cup of coolant a month. So I looked here for a solution which I found to be the rear coolant flange was leaking. After replacing the flange I didn't get air out of the system. I drove the car the temperature gauge never indicated that the engine was over heating it was summer time and I didn't check for heat. I learned my lesson I do not drive a car that the coolant was removed from until there is heat. I believe this caused the cracks in my amb head. My car always ran fine no misfires only got heat occasionally and usually going up hill under load . The upper coolant hoses were hot and were very firm as if under a lot of pressure, but the lower radiator hose was always cold. When the pressure was released by slowly opening the tank cap some bubbles would enter the expansion tank and the coolant level would rise in the tank. There was always air to bleed out of the metal distribution tube and the upper heater core bleed hole. I also replaced everything in the cooling system but the heater core and radiator. I decided that I had a bad head gasket sent it off to the machine shop for a pressure test and machining, don't know why but it passed the pressure test. I installed the head still had the same exact problem so I decided to take the head back off and sent it back to the machine shop and told them to perform a dye penetration test which revealed 6 cracks. I purchased a used head on e bay installed it with a new head gasket problem solved. This is my story I hope you solve your problem.

Combustion gas was entering your coolant passages? You could have used one of those tester kits sounds like.

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[tHatOne guY]

This is got me stumped. I always use the vacuum refill method as oppose to using the bleeder screw/lift the reservoir method and have never ever had a problem afterwards.

How much of a vacuum did you pull? and for how long?

[EuroxS4]

I know this is an old thread.However I decided to update you guys on what the issue is or was.I got it resolved.So after all that I thought that possibly i have a issue with the head gaskets.This turned out to be false.After closely examining the cylinder head i found that the head had crack between the valves in the combustion chamber.Further more this turned out to be my over heating cause.

[tHatOne guY]

I know this is an old thread.However I decided to update you guys on what the issue is or was.I got it resolved.So after all that I thought that possibly i have a issue with the head gaskets.This turned out to be false.After closely examining the cylinder head i found that the head had crack between the valves in the combustion chamber.Further more this turned out to be my over heating cause.

Good find.

Did you do look for exhaust gases in the cooling system or was the reservoir being pressurized by exhaust gases? Just curious what helped clue you in... Any cold start misfires?

How many miles? Tune?

[MikTip]

I can tell you that even bleeding the air from the system may not help....

It seems, after replacing my heater core...the water pump cant push the water back to the heater core at lower rpms????

Anyone else?

[EuroxS4]

Good find.

Did you do look for exhaust gases in the cooling system or was the reservoir being pressurized by exhaust gases? Just curious what helped clue you in... Any cold start misfires?

How many miles? Tune?

Car was bone stock but was overheating in the morning under load.If you turned engine off and cycled key everything was fine no more over heating.Resovoir was new looked a bit dark wasn't mixing coolant with oil per say but in the end a exhaust gas cooling system tester confirmed exhaust gases in the coolant.


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[EuroxS4]

I can tell you that even bleeding the air from the system may not help....

It seems, after replacing my heater core...the water pump cant push the water back to the heater core at lower rpms????

Anyone else?

Sometimes it needs to be driven for 30 to get the air out.Dont forget heater is the lowest point in the system hard to get all the air out.


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