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A4 Heater blows cold unless the car is driven or revved


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#1 happychappy

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Posted 05 December 2008 - 06:41 PM

Hi Guys

Hope someone can help, I have a 2001 A4 2.0 se multitronic with 80k miles.

I recently lost a small amount of coolant, over so many months I topped it up with a pint or less in 6 months, I alwys keep the pink stuff topped up. The Audi garage diagnosed a really tiny leak of a few drops from the rear of the cylinder head, the pressure was tested and everything was normal and their advice was try some K seal similar to radweld which should be ok, and if it doesnt stop it, then change the head gasket, but as it was such a tiny loss try the coolant seal first?

I put in the K seal and the coolant hasnt needed topping up since and any leak stopped straight away.

Anyway, two days ago the heater stopped working, when the car is at idle, all I get is cold or cool air blowing until I rev the engine or drive the car and then it gets warmer. The aircon works and the temp digital display reacts to changes and everything works ok on the display etc. The top and bottom hoses are hot and the radiator gets hot.

The temperature gauge climbs straight to midway 90c as normal and stays there all day and there is no collant loss, everything seems fine except the heater. I did 400 miles the other day, no coolant loss, no overheating etc.

I have checked the two heater pipes which go into the baulkhead and the top one is cold, but the bottom one is hot?

Anyone had this kind of problem, does it need flushing or could it be the heater valave and if so how big a job is this ? any advice gratefully received.

#2 shark_90

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Posted 05 December 2008 - 07:09 PM

It sounds to me like it could be air in the system. As you rev the engine, the water pump (ran off the cambelt I think) will run faster and will be able to shove more water around the system, masking the problem.

If I were you I'd change the coolant totally (well as much as you can with the water pump in situ). Get the car on a ramp or similar, remove the water filler cap, and drain the radiator by removing the lowest hose from the bottom of the rad.

I find the best way to fill the system back up again is to unscrew the bleed screws (not sure where they all are on the A4, on my S2 there is one on the top of the radiator and one on the hose leading to the heater matrix) and raise the expansion tank as high as you can. The pink stuff is called G12 - buy this from a dealer (you need the proper stuff, don't be tempted to use anything else). Not sure what the mix is as I don't know the capacity of the cooling system but you probably need 1-1.5 bottles of it. Stick that in and top up with water until water appears at both of the bleed screws, tighten them up, top up the water, and run the engine to circulate the water (put the expansion tank back first!).

That's the way I did it when I changed the coolant on mine anyway :beer:
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#3 MrAvant

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Posted 05 December 2008 - 08:13 PM

Could the heater matrix be slightly blocked and only when the pressure builds up when driving it forces the heat through.
K-seal and other stop leaks have been known to clog up the matrix.
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#4 cruiser647

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Posted 05 December 2008 - 10:16 PM

That would be poor advice from the stealer then. The heater matrix was a bugger to change on my V8!

Try the coolant drain first (or you could rev the engine with the filler cap open to let the air out)?

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#5 Luke

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Posted 05 December 2008 - 11:14 PM

This may be totally wrong but my bro in law recently had the same problem with his 5 year old Lexus. No hot air form the heater, cold air only. They thought it was head gasket. On inspection they found that the rad was knackered and the coolant was running out. Worth a look....
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#6 happychappy

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Posted 06 December 2008 - 08:48 AM

Guys

Thanks a lot for your replies, I am wondering about the K.Seal and the matrix, so thought of just undoing the heater pipe and connecting the hose to the valve going into the baulkhead and flushing it through, if this doesnt work then I shall do the full monty flush as shark suggests.

Thanks agian

#7 maersk

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Posted 06 December 2008 - 11:51 AM

Flush it backwads - the opposite way to normal flow ;)
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#8 stuartxrv

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Posted 04 December 2010 - 07:55 PM

Hi,
did you manage to resolve the heater problem?

I've just been done over after buying a 2004 Audi A4 Avant tdi sport from private seller. Not realising because i test drove the car whilst cold that the blowers would blow cold air unless going up hill then it would warm up. As soon as i levelled up or went down hill the temperature would drop. According to the service book, the water pump was changed not long ago! The bottom hose going to the heater matrix is getting hot whilst the top remains cold. I disconnected the top hose slightly which released 3 seconds of air befor coolant came through but it hasn't resolved the issue and after reading a few threads regards replacing the heater matrix it's a job i don't want to pay for!

Any help would be greatly recieved.
Thanks
Stuart

#9 cruiser647

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Posted 05 December 2010 - 10:21 AM

Hi! Welcome to TSN
What engine is your Audi?

Also, does the temperature guage get moving? And sit at 90? Is your coolant level correct now you've let some air out? And can you try that again to see what happens. Are your carpets dry inside?
Or does it move if you give the car a bit of wellie? Does the gauge then cool down if you drive normally?

Could be your thermostat - which if it's a 1.9tdi/2.0tdi is an easy job. If it's the V6 tdi, then it's a belts off job and £500-£600.

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#10 stuartxrv

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Posted 05 December 2010 - 06:39 PM

Hi cruiser,
Thanks for the welcome!

It's the 1.9tdi sport. Automatic. I went for a drive today and whilst driving around town the heating was luke warm, when i got on the motorway and opened it up, the heating went warm but not hot. It's not made any difference after letting the air out. The temp gauge does reach 90 and stay there. Is there any tests i can do to rule out the heater matrix being knackered, not having to replace this would lift a huge weight of my shoulders! Also noticed that the Eco light comes on and can't be switched off until it decides to go off itself. When it is off i've tried the air conditioning on minimum and it's freezing so i presume the compressor (Which according to the service history, was replaced last year) and the gas are ok! Is there a pressure switch on the system that can be shorted out to see if it's faulty?

Regards
Stuart.

#11 stuartxrv

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Posted 06 December 2010 - 02:07 PM

I've just got home now and had a feel of the matrix pipes, again the bottom one was hot the top one luke warm. Also felt the rad pipes, top hot bottom cold. Am i right in presuming this points to the thermostat not opening? Is it a bugger to change?

Thank again
Regards
Stuart

#12 stuartxrv

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Posted 06 December 2010 - 04:19 PM

Just been to a garage that does all my servicing to be told it's a common fault with Audi's. Water pumps are of poor quality and the impeller tends to break up causing parts to get clogged in the system. I'm not enjoying my 1st Audi experience!!!!!!!!!

#13 Scotty

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Posted 06 December 2010 - 05:34 PM

I've heard of it happening on the latest S4's but I've not heard of it previously. Either way it's not good.

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#14 stuartxrv

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Posted 07 December 2010 - 11:02 AM

Just tested my thermostat on the cooker and it's opening. So i guess we can rule that out!
Any more idea while i'm in the mood for stripping thins down?

Thanks
Regards
Stuart.

#15 cruiser647

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Posted 07 December 2010 - 01:41 PM

Have you got the new water pump? Should hopefully be a metal one.

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#16 stuartxrv

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Posted 08 December 2010 - 09:41 AM

Ten O'clock last night i got the car back together and run it up. Warm but not hot! Went to take it to the garage this morning and had no power. Car idled fine but there was nothing there when driving. Think i'll scrap it and go back to my trusted Fords!

#17 cruiser647

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Posted 08 December 2010 - 10:16 AM

Did you chagne the water pump?
Any lights on the dash? Does the engine rev up OK with stationery?

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#18 JamieHoward

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Posted 08 December 2010 - 07:26 PM

This thread grabbed my attention as I am experiencing the same problems.

For the last few days the heater will only become warm when driving, when stationary it gets cold again, also i noticed that using the washer jets makes the heater fan speed up?

Last night while driving at motorway speed, the temperature rose to nearly 130 degrees!

When i stopped i could hear some disturbing noises from under the bonnet, the top radiator hose was shaking along with the smaller hose from the reservoir, it sounded like a bag of marbles.

I suspect this is going to cost alot of money

#19 stuartxrv

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Posted 08 December 2010 - 08:49 PM

Hi Cruiser,

Garage said the water pump was fine! Found what looks like rad weld in the cooling system though so presuming the heater matrix is partially blocked. Going to get it replaced. Whilst i had the car in bits i must have broke what looked like an actuator/switch which resulted in my cars lack of power. Mike and the mechanics at Newlife garage sorted it out for me cheap as chips. Great bloke if anybody needs servicing/repairs around the Oldham area!

#20 krautmender

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Posted 09 December 2010 - 09:28 PM

Been reading this thread with great interest, at present I have an 2.0 FSI A4 in my workshop with all the symptoms that posters here have been talking about. Unfortunately for myself this car before entering my garage has been round the block so to speak and other workshops!

Once satisfied the heater matrix was clear, so far I have checked the water pump which was sound, radiator all tickity boo and clear, replaced the thermostat housing to eliminate any conflictions there, carried out a cylinder gas leak test and still no joy, but still there is one heater pipe hot and the other cold!

Ok before everyone starts rattling their keyboards I should first let you know I've been working on VAG vehicles now for over 30 years, 25 of those as an in dependant! I've have also consulted mates who are recent ex VAG master techs for a second opinion, we have all reached the same opinion.....the cylinder head probably needs to be removed for close examination.

All though there is not extreme pressure build up in the cooling system, it is quite possible of a slight combustion leak around cylinders 1 & 2 near the thermostat housing is producing enough pressure or air lock to prevent the coolant circulation on the heater circuit returning through to the water pump.

I would dearly love for someone to post a miracle cure for this problem that people are experiencing here, so I could provide my customer with cheery news! But it does look as though for the vehicle that I'm working on its either a head gasket or a hairline crack in the cylinder head!




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