Fan is on very high speed after replacing thermostat.

[06B7]

I replace the thermostat with a new one from Audi now when I star the car after couple minutes the fan kicks on very high speed never seen the fan blow so fast in 2.0t. Can someone tell me what's wrong.

[Charles.waite]

did you bleed the coolant system?

[FraggyA4]

Mine did that too for a a while till the thermastat opens and starts to flow the coolant. You can unplug the fuse to help your car warm up and make it open the thermastat.

[A-BlacK_MambA-4]

did you bleed the coolant system?

I would like to think he did, but you never know. What is the temp gauge showing when the fans kick up like that?

[06B7]

Yes I did unless there is a special way to do it and I don't know about I

[06B7]

You mean the fan fuse

[06B7]

I bleed the system the fan still running fast to fast but I turn off the car the temperature was in the middle but after I start the car again in five minutes the temperature was on dead cold and I know the car would not cool off that fast and I replaced the temp sensor last week. Also when I turn on the ignition the temp goes up and than goes down.

[Charles.waite]

Usually when the fan comes on full blast like that its because the ECU is sensing a fault. Did you remember to plug in the CTS on the lower rad hose?

Also do you get heat yet through the A/C? If the car has coolant then its not necessarily going to overheat. Drive the car around the block SLOWLY or sit in the driveway at idle with the heat on full blast. Let the engine get up to operating temp doing this. If you don't have heat at first, be patient. If you still don't have heat when the temp needle is getting towards the center it means you have a bubble in the system.

Edit: Just saw your post above. Sounds like you still have air in the system. Theres a bleeder screw on the coolant hardline right above the intake manifold. When your car is up to temp, shut it off and crack it SLOWLY. Be careful to not spray hot coolant over yourself. when coolant starts to flow out then close it again.

[06B7]

I have the heat but now my temperature gauge is stock. When I start my car the temperature goes in the middle and second later drops to little lower than1/4 and now the car been running for ten min temp still stock same place.

Usually when the fan comes on full blast like that its because the ECU is sensing a fault. Did you remember to plug in the CTS on the lower rad hose?

Also do you get heat yet through the A/C? If the car has coolant then its not necessarily going to overheat. Drive the car around the block SLOWLY or sit in the driveway at idle with the heat on full blast. Let the engine get up to operating temp doing this. If you don't have heat at first, be patient. If you still don't have heat when the temp needle is getting towards the center it means you have a bubble in the system.

Edit: Just saw your post above. Sounds like you still have air in the system. Theres a bleeder screw on the coolant hardline right above the intake manifold. When your car is up to temp, shut it off and crack it SLOWLY. Be careful to not spray hot coolant over yourself. when coolant starts to flow out then close it again.

[Charles.waite]

Sounds like you still need to bleed the coolant. Did you loosen the bolt on the coolant hardline above the intake manifold? You want to loosen it very slowly until air starts to bubble out. Once coolant flows solid then tighten it back up. Just don't unscrew it quickly or boiling coolant could spray on you.

Some people also unscrew the top of the reservoir pop it off of its mounts and hold it up as high as it can go to raise the pressure in the system and force air bubbles out more. Never tried it myself though.

[06B7]

I did that should or should i unscrew the bleeder and let the engine run

Sounds like you still need to bleed the coolant. Did you loosen the bolt on the coolant hardline above the intake manifold? You want to loosen it very slowly until air starts to bubble out. Once coolant flows solid then tighten it back up. Just don't unscrew it quickly or boiling coolant could spray on you.

Some people also unscrew the top of the reservoir pop it off of its mounts and hold it up as high as it can go to raise the pressure in the system and force air bubbles out more. Never tried it myself though.

[Charles.waite]

Which one? the screw or raising the reservoir?

[06B7]

SCrew or which one would you prefer I did what you told me

Which one? the screw or raising the reservoir?

[A-BlacK_MambA-4]

I have the heat but now my temperature gauge is stock. When I start my car the temperature goes in the middle and second later drops to little lower than1/4 and now the car been running for ten min temp still stock same place.

Did the same to me when I replaced mine. Like Charles said you need to bleed the system. I loosened the bleeder screw he is talking about and squeezed the coolant hose towards the front of the engine. I don't have a pic of it at the moment. Keep squeezing that hose and filling with coolant slowly. It will bleed all the air out I promise, it just takes some time and a little effort.

[06B7]

Did you did that with the engine running

Did the same to me when I replaced mine. Like Charles said you need to bleed the system. I loosened the bleeder screw he is talking about and squeezed the coolant hose towards the front of the engine. I don't have a pic of it at the moment. Keep squeezing that hose and filling with coolant slowly. It will bleed all the air out I promise, it just takes some time and a little effort.

[A-BlacK_MambA-4]

Did you did that with the engine running

Yea, and like I said what helped a lot was to keep squeezing that coolant hose up front. By doing that you are creating suction which helps the coolant get flowing again. And like I said slowly add coolant and then squeeze that hose a little bit. Leave the lid off the coolant reservoir and loosen the bleed screw a little.

[06B7]

Hopefully that going to help cause this is the second thermostat i am putting in just in three days cause the first one was leaking and when i start it never had the fan problem but i guess when i left everything open cause i was waiting for new thermostat than air got in there. I hope you right and i am going try it now thank you for quick respond.

Yea, and like I said what helped a lot was to keep squeezing that coolant hose up front. By doing that you are creating suction which helps the coolant get flowing again. And like I said slowly add coolant and then squeeze that hose a little bit. Leave the lid off the coolant reservoir and loosen the bleed screw a little.

[06B7]

Thank you my car runs normal now
[QUOTE=A-BlacK_Mambnd like I said what
helped a lot was to keep squeezing that coolant hose up front. By doing that you are creating suction which helps the coolant get flowing again. And like I said slowly add coolant and then squeeze that hose a little bit. Leave the lid off the coolant reservoir and loosen the bleed screw a little.[/QUOTE]

[CorneliusRox]

Thank you my car runs normal now

good to know!

Thanks for the info Joel

[A-BlacK_MambA-4]

Thank you my car runs normal now

No problem, glad I could help

good to know!

Thanks for the info Joel

No problem Corey. I ran into the same issue when I was doing the timing belt job on my B7 a few months ago. I called my dad and he passed that suggestion on to me, can always rely on my dad

[FraggyA4]

Same happened to mine took like an hours to bleed the system, didn't help that it was 35 degrees outside either.

[BoSNiaN]

Thank you my car runs normal now

What exactly did you do?

Also, if you do anything with the cooling system (tstat, sensor, coolant flush, etc) and your rad fans turn on 100% when you start the car, there is something wrong. Use vag-com and you might be able to narrow it down to what exactly is causing it but basically, the ECU is getting faulty (or not at all) temperature readings so will run the fans 24/7 just in case.

Also, appearing bleeding our cars as discussed in this thread doesn't really do anything according to some mechanics, especially running your heat on high because our cars have a dedicated (and different) system for that.

[nogovitsin]

Hi everyone! i got 2006 a4 2.0 T FSI and have the same frkn problem. In the beginning , after diagnostic in dealership , they sad a bad stat. So i replaced the stat , the engine check light went off and i have not any DTC's .But my both fans running at full blast after couple of second after you start the car. My next step was the CTS , replaced that. But the problem still there. When i turn my ECON off , the condenser fan still running.Checked all the electrical connections . Just read about the bleeding procedure. Sparkle of hope got in my head , did everything you said but fans still blasting.I ran the car till it reached the normal temp,shut it of and start open the bolt on the hard line slowly till i see the coolant then tight the bolt back up. Does it mean i bleed it properly?

[rings65]

Don't know if it is the proper way to do it or not, but after following all the same procedures (squeezing the lines and opening the bleed valve) I was still having issues as well. I finally set the temp to 'HI' and the fan speed on 1, and after driving around for 10 minutes after the engine was warmed up the air finally worked its way up to the reservoir and warm air starting coming out of the vents....

[nogovitsin]

Thank you my car runs normal now

Hi , are both of your fans running normal now?

[tavito_pr]

bringing this thread back to life...

First of all, my car didn't have any issues at all.
-decided to replace timing belt, water pump and thermostat while I was on the process.
-after everything was installed back, started bleeding the coolant by pumping the hoses, after that, started the car and kept bleeding the system because I knew there was air in it and the fans started blowing on HIGH.
-shut it off, took the bleeding screw out and had coolant coming out of it and put the screw back in.

-I'm getting REALLY HOT air through the vents, my engine temp is where it is supposed to be, but the fans starts full blast when car is cold and never stops

Temp last night when I did this it was 20deg F...

any help?
Thanks

[adam044]

Let it idle, all the air has to come out. Take it for a short drive also.

[tavito_pr]

Let it idle, all the air has to come out. Take it for a short drive also.

I left it idle for a while.. and this morning took a drive to work.. (25 min)... nothing changed

[adam044]

You idle it with the coolant cap off? How much coolant did it take once you filled it?

[Theiceman]

Watch here how he bleeds it ...

pic is worth a thousand words..

https://www.youtube.com/watch?v=g8lZ091tGJc

[Low and Behold]

EXACT same thing happened to me after I did my timing last month. Tried everything to get the fans to stop.

Finally I ended up just disconnecting the battery for a min and it fixed it. Have you tried that?

[tavito_pr]

You idle it with the coolant cap off? How much coolant did it take once you filled it?

Yes, with the cap off..
I would say it took a little over 5 liters of 50/50

- - - Updated - - -

EXACT same thing happened to me after I did my timing last month. Tried everything to get the fans to stop.

Finally I ended up just disconnecting the battery for a min and it fixed it. Have you tried that?

I was thinking about this... I'll try it tonight!

[Low and Behold]

I was thinking about this... I'll try it tonight!

Result?

[jrt20]

Since I can't find an answer anywhere and no one replies back after they have figured out what worked, I am going to supply what I did as detailed as possible and hope this helps someone else in the future.

I had this issue after changing the accessory belt, timing belt, tensioner, idlers, water pump, thermostat, and thoroughly manually bleeding the system by hand. Meaning squeezing the top and bottom rad hose method. I didn't have the vacuum on the reservoir contraption.

I reassembled the car, turned on the ignition, started the engine, and within 10 seconds of the engine running - both the radiator and condensor fan went full blast. All of the worst imaginable fears arose and I immediately shut the engine off. This happened three times before I figured it had to be some sort of learning thing with the ECU, but it wasn't. Still though, on the fourth try, I let the engine run in hopes it would get to temp with the fans running full blast, but it couldn't. The fans blowing that much air were able to keep the engine cool enough that the temp gauge hovered around the quarter tick mark. With that being said, I was starting to get heat coming out of the vents, so I knew that I was at least getting circulation through the engine block which means the engine couldn't possibly be over heating.

So, I shut the engine down and did a little more digging but couldn't find any answers as to why the fans where kicking on full blast. I tried disconnecting the battery and reconnecting it, but that didn't work. Finally, I just made up my own mind by disconnecting the fans all together and letting the engine get to temp since I was sure that there was more than enough coolant in the system. Keep in mind that it's December in Ohio and my garage was in the 40's so I didn't have to worry too much about temps rising too quickly. Letting the engine run without the fans seems risky, but turns out the Audi cooling system is very efficient at controlling temps at idle than one would think. So I let the engine get to temp and waited until I could start feeling the upper radiator hose warming up. This is when I knew that I had full system flow. At this point I shut the engine down, reconnected the fans, and took the car for a short drive (few miles) over some minor hills which happened to force air bubbles to the highest point in the system, the heater core hose. The system was bled while it was in the garage, but a bubble had worked its way up to the heater core hose, which having been bled initially was very easy to burp that bubble out after I got back home. Keep in mind, this hose is a bear to break free if it wasn't done while initially bleeding the system. Best to get this hose free while the system is cold. So, I knew the bubble was in heater core hose because while driving, I stopped in a parking lot to see if there were any changes in idle, noises, or any thing notably different. One thing changed. At idle, cold air started blowing out of the vents, but upon a little engine rev heat immediately came back. The heat would dissappear once again at idle, BUT the engine temp gauge didn't budge. So, I drove back home, pulled the heater core hose back and out came the air followed by a stream of coolant.

Other things I noticed about this work are the following:
The idle is a little bit smoother
The engine is peppy and pulls harder now.
There used to be a weird rev fluctuation as the engine was getting to temp(before the quarter tick mark), but that is now gone. This was either a timing issue due to the stretched belt or the fact that engine wasn't heating up quick enough (bad thermostat) which would lead to a weird open/closed loop fueling problem. Many threads attribute this fluctuation to a possible bad torque converter.

I hope this explaination goes on to help someone out.

[BenMTL]

Did you replace the temp sensor at the same time? It is probably faulty.

[Okedokey]

I would say to everyone, there is reason for this. Its a fail safe measure so that no matter what the car's cooling works. I find that removing the battery cables and shorting them (not the battery) for 15 minutes solves this issue. You will need to go into VCDS to clear all faults and readapt everything, but I do that on a semi-regular basis anyway. Electronics (especially when older) goes out of spec.