TDI 75 Running Cold...

My 2005 TDI 75 temperature gauge only gets to 80 degrees at motorway speeds, but quickly drops back down to about 60-65 degrees around town. Today, having had a new starter motor fitted at my local garage,- I was told by the mechanic -( who previously worked for Audi) that it rose up to the optimum 90 degrees, but only when the climate control was turned off. He reckons that the engine fan is coming on in tandem with the climate/interior fan, preventing the engine from coming fully up to temperature- mentioned something about a fan module or ECU fault..... I'm booked in to my local Volkshop on the 27th Nov to look into this... Timmus noticed the problem first when he was fitting my DIS and thought it perhaps a Thermostat or coolant temp sensor.. Has anyone out there had this situation and found it to be related to the climate control/engine fan correlation?... I would be curious and grateful to hear any and all -"Been there, Done that" stories in a similar vein... Cheers D.🤚
 
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Robin_Cox

Member
thermostat. I needed to fix this on both of my TDis.

Before replacing it, my car would only almost get up to 90 when running at full power for some time when not using the heating (ie spring, autumn) ; on a cold day when you've got the heat turned up in the cabin, higher air speed over the heat exchanger etc you can watch the engine cooling down more or less in real time if you're sitting at idle (and if the thermostat is duff, you might never see it get to 70 before dropping off again). In one car the temp sensor also needed replacing - after replacing the thermostat intermittently the needle would get nearly up to temperature and then suddenly drop like a stone to nothing - then return to 90 after going over a pothole, all completely randomly. VCDS suggested that there was an 'open to ground - intermittent' fault with the sensor ; switching it was an immediate change to normal behaviour - but the thermostat was the main reason for it running cold to begin with in both cars.

Didn't notice the comment from your mechanic about it getting to 90 with the climate control off - so possibly have a think about the fan controller as well, but I would still look at the thermostat to begin with as these can be 'lazy' even if they haven't failed completely.

Best of luck!
 

steveb

A2OC Donor
My fan runs all the time with air con on, slowly sometimes but the point is the car gets up to 90 as it should. as has been said, thermostat or the temp sender can be faulty

Try running the car on econ and see if it behaves correctly ?
 
thermostat. I needed to fix this on both of my TDis.

Before replacing it, my car would only almost get up to 90 when running at full power for some time when not using the heating (ie spring, autumn) ; on a cold day when you've got the heat turned up in the cabin, higher air speed over the heat exchanger etc you can watch the engine cooling down more or less in real time if you're sitting at idle (and if the thermostat is duff, you might never see it get to 70 before dropping off again). In one car the temp sensor also needed replacing - after replacing the thermostat intermittently the needle would get nearly up to temperature and then suddenly drop like a stone to nothing - then return to 90 after going over a pothole, all completely randomly. VCDS suggested that there was an 'open to ground - intermittent' fault with the sensor ; switching it was an immediate change to normal behaviour - but the thermostat was the main reason for it running cold to begin with in both cars.

Didn't notice the comment from your mechanic about it getting to 90 with the climate control off - so possibly have a think about the fan controller as well, but I would still look at the thermostat to begin with as these can be 'lazy' even if they haven't failed completely.

Best of luck!
Thanks for telling me this, I'm gonna get it looked at, I just wanted to know if I was barking up the right Tree..👍
 

O07JESTER

Member
My fan runs when climate is on,so did my Touran.My temp goes up when driving but drops when moving slowly.I guess my thermostat is stuck open.Annoyingly I changed it this year (euro car parts circolli).It's on my list to do but will get OEM or at least as good this time
 

Lindsayt

Member
I've been replacing my thermostat today. Just need to finish it off tomorrow by refitting the alternator and auxilliary belt tensioner. And replacing the litre or so of lost antifreeze.

It was not getting to 90 degrees round town. Would get to 90 degrees going up the M62 over the Penines and would drop down to 65 degrees again on the descent to Rochdale. Making the temperature gauge read like an altimeter. That was in the wet and windy 4 degree weather this week. It was drinking more fuel than usual too.
 

Robin_Cox

Member
My fan runs when climate is on,so did my Touran.My temp goes up when driving but drops when moving slowly.I guess my thermostat is stuck open.Annoyingly I changed it this year (euro car parts circolli).It's on my list to do but will get OEM or at least as good this time
I used ECP Circolis on both of mine and they have both been fine - I know a few people here have used them without issue, but as you say, perhaps the fact that they're as cheap as they are may mean the odd dud one is in circulation and it's been your bad luck to have fitted it.
 

O07JESTER

Member
I used ECP Circolis on both of mine and they have both been fine - I know a few people here have used them without issue, but as you say, perhaps the fact that they're as cheap as they are may mean the odd dud one is in circulation and it's been your bad luck to have fitted it.
I had no hesitation fitting the circolli thermostat tbh.But I guess at the price it's inevitable that a dud will be part of all that are sold.its more the inconvenience to change it than the cost.Im sure even OEM's have a calculated amount of "duds"
 

Silverpig

Member
If this is such a common occurrence then surely it begs the question why there are so many dud thermostats around? My TDi also has an irregular running temperature in cold weather, I’ve changed the the thermostat twice to sort it out. In warmer weather it heats up perfectly.
 

steveb

A2OC Donor
If this is such a common occurrence then surely it begs the question why there are so many dud thermostats around? My TDi also has an irregular running temperature in cold weather, I’ve changed the the thermostat twice to sort it out. In warmer weather it heats up perfectly.
Have you tried the temp sender ? the car might be up to temp but the gauge is not telling you the truth ?
 

Silverpig

Member
I don’t suppose you solved this did you? Mine is driving me nuts at the moment! I’ve changed the temperature sensor and the thermostat to no avail. The thermostat was a Circoli and the sensor was sourced from German and Swedish.
 
I changed the Thermostat but, now and again on cold mornings, it throws up a fault/engine light. I'm told it's the anti shudder flap sticking(there's a kit online you can get I'm told)- After about 3-4 hours it goes off and stays off for about two-three weeks.... so, at the moment I'm not too bothered about it cause I think I know what it is.... Timmus will know more, give him a PM.👈
 

johnyfartbox

A2OC Donor
Would it make sense to dip a new thermostat into a pan of boiling water first to test a thermostat or does it not work like that.
 

audifan

A2OC Donor
Best bet is to source parts in this case directly from Audi. There are a lot of poor quality parts working through the system now in genuine LOOKING packaging.
 

Pinkythelabrat

A2OC Donor
I’ve used the circoli ones from ECP no problem in the past. £3 I think. You could have a feel of the hoses around the thermostat to see if it’s working without removing it and save yourself the trouble. If the engine is started cold and the pipe from the thermostat to the radiator starts to get warm quickly, before the engine has warmed up the coolant loop, then that would point to a duff thermostat... I think... but then I’m not great mechanically!


Sent from my iPhone using Tapatalk
 

RAB

Technical Specialist 1.2 TDI
The temperature displayed is not the cylinder head temperature. According to a user on the German site, 90 deg C on the A2 gauge is anywhere between 70 and 105 deg C! So if you want to know the actual temperature, use VCDS.

An A2 Tdi can generate so little heat (especially a 1.2) that in really cold weather with the heater on, the gauge doesn't reach 90 with a correctly functioning thermostat. But in ambient temperatures above zero, the gauge should always reach 90. If not suspect the thermostat.

RAB
 
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Silverpig

Member
Nice tip! I was going to refit the old one just to compare, but I can’t face the aggravation of undoing the bottom bolt at the moment. The annoying thing is that prior to the coolant leak it had been running up to temperature perfectly, it’s only since attending to that and replacing the sensor and flange joint that it started misbehaving. I then changed the thermostat to no real change, and then refitted the old sensor to finally put an end to the leak from that area!

It’s continuing to find ways of driving me nuts but I’m going to leave it alone for the time being as I’d rather have it running cold than risk having it leaking fluid again.
I’ve used the circoli ones from ECP no problem in the past. £3 I think. You could have a feel of the hoses around the thermostat to see if it’s working without removing it and save yourself the trouble. If the engine is started cold and the pipe from the thermostat to the radiator starts to get warm quickly, before the engine has warmed up the coolant loop, then that would point to a duff thermostat... I think... but then I’m not great mechanically!


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oowee

Member
Just drove to Chepstow in mine today and it has done exactly the same thing. Never wants to go above 85 and then when on the M$ it dropped beck to 65. Its in for service and MOT on Wednesday so will get it looked at then.
 

PlasticMac

Member
Isn't it possible to restrict or control the volume of forced air through the radiator to allow the engine to reach it's designed (max thermal efficiency) temperature? Can't be good to have the engine running 20/30 degrees below the optimum, with little or no coolant circulation. Even the oil may not reach the correct viscosity.
I realise this is all a bit theoretical, but if I were running a TDI, I'm sure I'd be investigating ways to do this.
Mac.
 
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