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No heat in January! Audi A4 mystery

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Two months ago (Oct. 2012) the heat went out in my car. I took it to the dealership where they replaced the radiator, thermostat and did a full coolant flush. The heat worked for two months. I drove my car 1400 miles to/from Ohio over Christmas. Three days ago I noticed that the heat only worked for about 15 seconds and then turned cool. I can turn my heat on every few minutes for about 15 seconds of hot air and then it goes cool. I checked the heater core hoses–they are both warm. The coolant reservoir is full. My mechanic looked at it today (also checked the heater core which is fine) and his best guess is that the water pump he put in 3 years ago is failing. When he ran the car to 2000-3000 rpms the heat stayed hot. He wants to replace the water pump. Should I let him or go back to the dealership?

Don’t know that you’ve got much choice. Sounds like there would be a circulation issue but could be due to a bubble in the system which requires bleeding the air out of the system, or heaven forbid there is a head gasket failure, introducing combustion gases into the system. I guess I’d have him check for both first, but ya gotta have heat.

@mvymermaid, how old is the A4?
how many miles?

To me, it sounds like a heater core issue.
Your heater hoses should be hot, not warm.

To me it sounds like a blend door issue,

it could also be a vacume leak that may or may not control (I dont know if that car has it or not) the flap that controls the air direction from the heater core.

Yeah but if its a blend door or vacume issue, it shouldn’t work with a high rpm. Should be just the opposite since vacume would be higher at lower rpm. Whether the hoses are warm or hot though is kind of subjective but if they are both warm kind of indicates there is water getting through the core. What concerns me is that this is the way my diesel was when the head gaskets went except it would stay warm at higher rpm, not be intermittant.

  1. probably your heater core is clogged up, famous on all audi’s, easy fix all you gotta do is locate the hoses, the’yre to the right of the battery covered by a plastic shroud, remove that and you’ll see 2 hoses side by side, they have clamps that you can remove with channel locks pliers. pull the hoses off, then use a garden hose to flush water into opening, lets water flow for 30sec, then repeat to other side, so that twice for each, hook hoses back up and should be good to go.

  2. if it was your water pump your car would be overheating to the max, like your needle would all the way on hot and your coolant would be boiling in your tank, it’s not your waterpump.

  3. its either your heater core needs to be flushed, or maybe your heater control module is crapping out.

i’ve owned a few audi’s, and have worked on all of mine making custom turbo kits to the basic oil change…let me know if you need anything else.

Thanks to all! The heater core is good–it’s been checked out.

The car isn’t overheating at all. My mechanic says the heat does stay on at higher rpms so perhaps it is the head gasket? How would we test if it was the heater control module? Everything comes on as normal–the blower, the plenums open (I can hear them) and it runs, but turns cool after 15 seconds. The longer I run the car (over 25 minutes) the longer the heat will stay on–so if I’m driving for longer than it takes me to get to work the heat will keep going for over 15 seconds–up to a minute before going cool. I found that out yesterday when I was running errands.

I will see my mechanic tomorrow (I live in a small island community) so can ask him about these suggestions and then my car goes back into the shop on Monday. Just really don’t want to keep throwing $$ after “possible” cures.

The car is a 1999 Audi A4 wagon.

113000 miles

It could be air is trapped in the system. Put the car up on ramps and run the engine with the radiator cap off. Let it warm up to operating temp and it should purge the air with the heater on full blast. You will also see the fluid moving in the radiator. Your car would cook if the pump was not flowing. Are you loosing any fluid?

@myvermaid, why are you so sure the heater core is okay?

Did your mechanic visually verify that it has good flow?
Did he take off both hoses and hook up a water hose to the heater core to make sure it isn’t plugged?
If he didn’t do that, I wouldn’t be sure the heater core is okay.

knfenimor–do you mean the car should be tilted? is it just the front end up on ramps? i am not losing fluid. how would air get into a closed system like that? seems like you and bing are on the same page with this. would the cold weather keep my car from overheating this time of year?

Yes, he told me he did that to the heater core.

@myvermaid, thank you.

hey folks–just wanted to update you all:
my on island mechanic put in a new water pump (it was leaking a bit) and gave me a great price on it since he put the last one in 3 years ago. he then flushed the heater core. alas–still no heat. so i took it to the dealership off island where they ended up “soaking” the heater core overnight in CLR and then flushing the crap out of it. voila! heat! it’s been a week and heat still cranking.

so in the end it WAS the heater core. it was just wicked clogged up.

many thanks to all who took the time to comment and make suggestions. great forum!

@bing I would be under the assumption the higher the rpm the greater vacuum pressure. Correct me if I am wrong. Do you have a temp gauge and if so what are your observations? A bad thermostat could be a possibility.

@myvermaid congratulations! I actually use CLR to clean coffee pots. Apparently it has automotive applications also!

If I may ask, what is the coolant service interval according to Audi?

@barkydog I’m not a mechanic so can’t really explain it but if you put a vacuum gauge on and rev the engine, the vacuum goes down. If you remember way back in the old days when they had vacuum operated windshield wipers and you’d step on the gas to pass someone and the wipers would slow down or quit due to a lack of available vacuum. Let up on the gas and the wipers would work again. I can’t tell you why though.

I sent you a message of apology also for having fun at someone else’s expense.

@db4690 According to my Audi Owners/Maintenance/Service manuals (and I paraphrase here),
“Coolant service? We don’t need no stinkin’ coolant service” . “This is GERMAN coolant!”

Of course I don’t believe that for a minute, I’ve drained and refilled twice in 80K mi.