Radiator fans / Coolant temp sensor / Thermostat issues

[SteveR83]

Hoping someone might be able to shed a little light on an issue I am currently having with my 2008 A3 8P 1.9TDi.

I noticed recently, in the last couple months, that I was getting noticeably worse mpg, and have now since realised that both the radiator fans come on immediately when starting the car, even from cold first thing in the morning. They stay on all the time when driving too. They even come on if I just turn the ignition on without actually starting the engine. They never stay on after removing the key though like I have seen others having issues with.

The car is also not getting up to normal temp, it gets no further than about 70 degrees, but then pretty much stays at that temp. Also with the climate control system on, the ECON button is on and cannot be turned off. I have one of those cheapo bluetooth obd scanners which I have used to scan for errors with the Torque Pro app, but it doesnt find any problems.

So, I have now removed the 50A bolted on fuse to stop the radiator fans coming on at all. I was thinking them being on might be why the car couldn't get up to 90 degrees, but even without the radiator fans on it is still getting no further than 70 degrees. The ECON button is also still on and cannot be turned off.

I have read various threads about similar issues, but am unsure where this problem may be - The radiator fans themselves, the coolant temp sensor, or the thermostat. If the thermostat is faulty, could that cause both radiator fans to run at full speed immediately? If it was a coolant temp sensor, wouldn't I get an error code?

Hopefully someone has had the same issue before!?  Any help appreciated.

[Magnet]

Hello Stephen and welcome. 
If this were mine, I would treat this on a one thing at one time principle. 
Not reaching temperature is typical of a failing/failed thermostat, so that would need investigating and then renewing to ensure the car is operating at the optimum temperature. Once it’s operating at 90 degrees, you can then set in motion a plan of action for the remaining issues. 
Kind regards,

Gareth. 

[SteveR83]

Hi Gareth, and thanks.

I think you're probably right, it makes sense to start with a new thermostat.  I was hoping it would be the temp sensors as I could attempt to replace those myself.

Do you happen to know if a dodgy thermostat could be causing both radiator fans to be constantly on?  That is the main reason I am not quite sure..

[SteveR83]

Hi Jason, thanks I will have a look at the relays this evening.

[cliffcoggin]

2 hours ago, SteveR83 said:

Do you happen to know if a dodgy thermostat could be causing both radiator fans to be constantly on?  That is the main reason I am not quite sure..

The thermostat does not control the fans, that is the job of the temperature sensor. (Strictly speaking, any switch that is controlled by temperature is a thermostat, but let's not be distracted by that as it is contrary to convention in cars.)

That the indicated temperature goes no higher than 70 without the fans suggests to me that either the thermostat remains open all the time or that the temperature reading is wrong. Does the temperature reading drop to the bottom of the scale when the engine is cold? Do you have a way to independently measure the temperature using a hand held infra red meter for example?

At this stage I can not say whether the ECON fault is related to the temperature fault. I suggest you ignore it for the moment, but bear it in mind if you get other indications of a general electrical problem.

[SteveR83]

9 minutes ago, cliffcoggin said:

The thermostat does not control the fans, that is the job of the temperature sensor. (Strictly speaking, any switch that is controlled by temperature is a thermostat, but let's not be distracted by that as it is contrary to convention in cars.)

That the indicated temperature goes no higher than 70 without the fans suggests to me that either the thermostat remains open all the time or that the temperature reading is wrong. Does the temperature reading drop to the bottom of the scale when the engine is cold? Do you have a way to independently measure the temperature using a hand held infra red meter for example?

At this stage I can not say whether the ECON fault is related to the temperature fault. I suggest you ignore it for the moment, but bear it in mind if you get other indications of a general electrical problem.

Thanks, that is what I was trying to understand.  It didn't seem likely to me that the thermostat would cause the fans to come on.

The temperature guage appears to be working normally, it drops to the lowest reading when the engine is cold and rises to about 70 within the first 10 minutes of driving and then stays there - It doesn't behave erratically or jump around.  On the cheap bluetooth obd scanner, it shows the coolant temp at the same temp the dash says.

I don't have an infra red meter unfortunately, but when I get a chance I was planning on running the car from cold and feeling the hose from the thermostat to the radiator to try and see if it slowly warms up which I believe would suggest the thermostat is stuck open?

[SteveR83]

9 minutes ago, jasonj said:

Hi Stephen , The fact the Radiator fans are on from starting is not normal . This will and does effect Temperature especially at this time of year . It would normally start operating at 90 degrees Celsius .

The logical course of action is to unplug them and then keep an eye on the temperature gauge and when you reach 90 c , plug them back in .  And then you will know. Jasonj 

Thanks, yeah I have already taken the bolted fuse off for the radiator fans and have driven a few times with them disconnected.  Even without the fans on at all the temperature guage won't get above 70 degrees.

[Stevey Y]

5 hours ago, jasonj said:

Hi Stephen , There are few Circuits in the Cooling System along with the Heater Matrix . If you do not have any leaks then the Thermostat will be in the open position . Because it is open this means the temperature will rise at an overall incline . 

The normal operation would be Primary Circuit . 93c .Thermostat opens  Secondary Circuit . Temperature drops . 

so you have two issues 

1: Check Relay / Short to ground wiring at radiator 

2: Thermostat . Check . Jasonj 

Ps unless you have the heater on with fans running constantly in this weather whilst driving wind chill factors 

Hi perhaps you would like to expand on a few circuits, you have completely missed the point of the guys post the fact that the car is still not getting up to running temp with or without the fans, I completely agree with Cliff/ Gareth that solving one problem at a time and once the car starts achieving its proper temp, then worry about turning the fans off, the problem I suspect is a faulty fan control unit, the silver box on the fan pack and as they are both running and he can't turn the air con off that is the most likely culprit, as for wind chill the guy lives in Sussex not Siberia, my car used to take a while to warm up at temps around +2 and as soon as the ambient temp got to +5-6 it got very warm, are you a salesman for YouTube sites as they are only worth looking at once you have established the problem, a very wise man I studied under once said, you can spend a lot of money and time trying to cure the the effects of a fault but you really should spend the same time and money curing the root cause. 

[cliffcoggin]

On 3/5/2024 at 1:47 PM, SteveR83 said:

The temperature guage appears to be working normally, it drops to the lowest reading when the engine is cold and rises to about 70 within the first 10 minutes of driving and then stays there - It doesn't behave erratically or jump around.  On the cheap bluetooth obd scanner, it shows the coolant temp at the same temp the dash says.

 

In that case it is almost certain the thermostat needs to be renewed. It isn't a difficult job, but getting rid of the inevitable airlock afterwards can be. (If the cabin heater does not work after changing the thermostat you have an air lock.)

Let us know if the engine reaches normal temperature afterwards and we can then move on to the fan problem.

[SteveR83]

I think I have come to the same conclusion Cliff regarding the thermostat, and I think Stevey is also probably right about the fan control unit.

Changing the thermostat looks beyond my ability unfortunately, especially considering the lack of time I would have during a weekend in case anything went wrong!  I will be taking it to my local garage next week who will change the thermostat and look at the fans at the same time - Hopefully there is a simple wiring issue with the fans but if it needs a whole new unit then so be it.

Hopefully that will sort all my issues, as Stevey says the ECON issue is hopefully a byproduct of the faulty fans.

Thanks for all the suggestions, will let you know how it goes!

[Stevey Y]

4 hours ago, SteveR83 said:

I think I have come to the same conclusion Cliff regarding the thermostat, and I think Stevey is also probably right about the fan control unit.

Changing the thermostat looks beyond my ability unfortunately, especially considering the lack of time I would have during a weekend in case anything went wrong!  I will be taking it to my local garage next week who will change the thermostat and look at the fans at the same time - Hopefully there is a simple wiring issue with the fans but if it needs a whole new unit then so be it.

Hopefully that will sort all my issues, as Stevey says the ECON issue is hopefully a byproduct of the faulty fans.

Thanks for all the suggestions, will let you know how it goes!

Hi you may get lucky and the fan control pack is bolted on AKA hybrid and for reasons only known to Audi on some models its all one unit with the fans, either way unless you purchase from Audi the parts are pretty cheap as a lot of companies have stock for the older cars stuck up their backside so are pleased to get rid at a decent price, example I did a replacement pack on my mates 2013 Transit Frauds wanted over £400 for the unit, eventually got one for £140 with a two year guarantee and talking to the guy they used to supply Fords when they ran low on stock from Brazil.                                                         

[cliffcoggin]

On 3/6/2024 at 3:04 PM, SteveR83 said:

  I will be taking it to my local garage next week who will change the thermostat and look at the fans at the same time -

Do please let us know the outcome.

[SteveR83]

So have a small update on this for anyone interested.  My local garage did squeeze me in to take a look but unfortunately didn't have time to actually replace the thermostat.  They did agree that it's almost certainly in need of replacing and the cause of the coolant temp not getting to full temp. 

They also ran a scan and confirmed that the fan control module had error codes so the whole unit needed to be replaced.  Think they said the genuine part was about £280 but also said if I wanted to buy non-genuine they would fit for me.  Does anyone have experience of these cheaper radiator fan units?  They any good, or just a false economy?

Also, I am trying to find the exact part number for the fan unit, is there anywhere I can find that online?  There seems to be a few variations of this part depending on year etc/engine etc.

[Stevey Y]

4 hours ago, SteveR83 said:

So have a small update on this for anyone interested.  My local garage did squeeze me in to take a look but unfortunately didn't have time to actually replace the thermostat.  They did agree that it's almost certainly in need of replacing and the cause of the coolant temp not getting to full temp. 

They also ran a scan and confirmed that the fan control module had error codes so the whole unit needed to be replaced.  Think they said the genuine part was about £280 but also said if I wanted to buy non-genuine they would fit for me.  Does anyone have experience of these cheaper radiator fan units?  They any good, or just a false economy?

Also, I am trying to find the exact part number for the fan unit, is there anywhere I can find that online?  There seems to be a few variations of this part depending on year etc/engine etc.

Hi try LLL carparts they have a catalogue online the only bit you will needs your VIN code that should give you the part number, with regard to aftermarket as long as you don't buy Made in China they are generally spot on as Audi don't make the parts they buy them from Valeo or Febi or whoever sells to them at a preferential price.

Steve.