# Normal running temp?? Overheat? Gauge fault?



## dsisco (Jun 17, 2015)

As per title, I have just purchased a MK1 225Q,

on the way home on the motorway I noticed the temp go past 90 on the dash to about 1/2 way to the next line,

in slower traffic the guage moved back closer to 90,

I have tried the 49c & the temp goes to about 103-107 max when left idling, 51c only goes to 90 & holds steady,

The vehicle has just had new coolant temp sensor & fan switches fitted just recently,

any help would be much appreciated>


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## Hoggy (May 8, 2002)

Hi, Coolant temp will rise when left idling as no airflow through radiator until fan cuts-in.
Surprised coolant temp drops when slowing down, usually that is caused by a failing water pump.
Change coolant temp sensor first using an OEM sensor,cheap & easy, but I suspect it's the water pump.
http://www.wak-tt.com/tempsensor/tempsensor.htm
Forget about using Code 51 as it always settles @ 90. Code 49 is coolant temp.
Hoggy.


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## Hoggy (May 8, 2002)

Hi, Normal running coolant temp is 90 ish on Code 49.
Gauge is weighted to read 90 if coolant temp (code 49) is any where between 82 & 100 ish.
Hoggy.


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## dsisco (Jun 17, 2015)

Thanks for the quick reply,

I have left the vehicle with the workshop, to investigate further, once I get it back tomm I'll do some more testing,

I have only driven the car twice, once when I bought it & 2nd to the workshop as I'm scared of cooking the engine,

I had my gauges tested because my fuel gauge is out, they didn't mention anything about the temp,

Could it be bad thermostat? Or u think water pump? Timing belt & pump was changed about 20,000kms ago

Don't know when thermostat was last changed


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## chrissey22000 (Nov 14, 2014)

It's not obvious to me why a dropping water temperature at lower engine speeds would suggest a faulty water pump, even if the pump is not working efficiently, it's capacity will increase with increasing speed and at lower engine speed, the coolant transfer from the hot engine would drop and the temperature would rise.

My TT runs up to approx 95C with harder driving and then if you slow down and/or in stationary traffic, it will go up to the 102-103C mark and the fans cut in.

It could be a sticky thermostat, not open enough at high load but open more than needed at lower engine load and therefore more cooling effect with higher flow through the radiator?

Just a thought, if it helps.


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## Hoggy (May 8, 2002)

Hi, If the water pump impellor is damaged it manages to move the water through the system at low rpm but at higher rpm it thrashes through the water rather than moving it around the system to cool it, so at lower rpm the flow increases & coolant temp reduces.
Hoggy.


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## DazWaite (Dec 4, 2012)

Hoggy said:


> Hi, If the water pump impellor is damaged it manages to move the water through the system at low rpm but at higher rpm it thrashes through the water rather than moving it around the system to cool it, so at lower rpm the flow increases & coolant temp reduces.
> Hoggy.


That's very true Hoggy....

Daz


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## DazWaite (Dec 4, 2012)

Don't rule out Head gasket failure or even a cracked head,both can have this effect of higher rpms along with higher temps and lower rpms equalling lower temps....

A few fins missing on water pump would be more likely imo

Daz


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## 3TT3 (Aug 30, 2014)

The TT temp gauge is a funny thing cos of the "damping"

1.After the 'investigation at the workshop" if the problem persists I would follow Hoggy's advice in relation to the first thing to do..get a new oem coolant temp sensor,unless your sure an oem one was put in before you bought it/
Did you enquire as to why the sensor and fan switches were changed recently?
You can try below stuff even as is.

It could of course be water pump/wotever but (and this is assuming the replacement fan thermostat is ok).
I changed my sensor recently..the readings were all over the place..
a.Do your own tests with 49c on all the time
You have to have the a/c switch in the on position to get readouts ,but if you also turn on econ the fans wont be running if the water temp is below about 98C
b.If the fan/s thermo switch is ok the fan should turn on at around 100c and off around 98

c.you say the temp goes 103-107 at idle, well the temperature range sounds about right 4 degrees but actual readout is high.
Mine ,now with a properly reading sensor goes from 98-102.

lets say Ive come back from a bit of a blast,temp 95/96 when the car stops moving.. or you can test in traffic too then the readout temp will go up quite rapidly..you can hear the fans kicking in around 100 but the water may get to 103 cos of all the component heat ,continue idling and it settles into a 98-102 readout cycle with fans on fans off.


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## tt92103 (Jun 4, 2015)

dsisco said:


> As per title, I have just purchased a MK1 225Q,
> 
> on the way home on the motorway I noticed the temp go past 90 on the dash to about 1/2 way to the next line,


Where do you read 90 on the dash? My coolant gauge has no numbers or units... (?)
2001 225Q


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## bigdodge (Apr 22, 2012)

In the picture the needle is sitting at 90.


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## Hoggy (May 8, 2002)

Hi, UK pod has numbers.








Hoggy.


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## dsisco (Jun 17, 2015)

Drove the car last night & today, temps seems to stabilise on 100c going up to 103c max,

Haven't driven on the motorway yet, but after spirited driving & sitting at idle its stable from 100-103c according to 49c

Thoughts????


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## Hoggy (May 8, 2002)

dsisco said:


> Drove the car last night & today, temps seems to stabilise on 100c going up to 103c max,
> 
> Haven't driven on the motorway yet, but after spirited driving & sitting at idle its stable from 100-103c according to 49c
> 
> Thoughts????


Hi, May get to 100/103 while idling until fan cuts-in to cool, but should be around 90 ish on Code 49 while driving/moving normally.
Hoggy.


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## dsisco (Jun 17, 2015)

Hoggy said:


> dsisco said:
> 
> 
> > Drove the car last night & today, temps seems to stabilise on 100c going up to 103c max,
> ...


Took the car for a good run today,

Mixed driving

freeway running constant at 80-90kmh temp stays around 100-104c,

Stop & go driving cars around 100-104 also

Sitting In traffic its climbs up to 107-8c

thing I noticed, the harder I drive it eg more rpm the temp seems to drop a degree or 2,

I also noticed my fans didn't kick in high speed unless I have the heater on full

With the heater on full & fans on, I can get the temp down from 107c to 99c if I rev the vehicle while stationary

What do you guys think i should start??

Change fan switches & coolant temp sensor again even though they're only 1 month old? 
Thermostat? Or coolant flush?


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## Dash (Oct 5, 2008)

If you've done the sensor recently, I can't see why changing it again would help.

My themostat wasn't working right when I got my car, and I think it's gone again 5-6 years later. But, my temperature is going the other way (both times), and the car can't maintain temperature.

Do the radiator fans come on when you've stopped and it's warm? They'll continue to run when the engine is off so it's easy to hear if they are going.


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## Hoggy (May 8, 2002)

Hi, You need to confirm whether the high coolant temp is correct first.
Use a meat thermometer in header tank as soon as it's safe to remove the cap & compare with Code 49. May not be exactly the same but should be within a few degrees. 
Otherwise replace temp sensor cheap & easy & use OEM sensor.
http://www.wak-tt.com/tempsensor/tempsensor.htm
Hoggy.


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## dsisco (Jun 17, 2015)

Dash said:


> If you've done the sensor recently, I can't see why changing it again would help.
> 
> My themostat wasn't working right when I got my car, and I think it's gone again 5-6 years later. But, my temperature is going the other way (both times), and the car can't maintain temperature.
> 
> Do the radiator fans come on when you've stopped and it's warm? They'll continue to run when the engine is off so it's easy to hear if they are going.


The fans don't run once the engine is off,


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## Hoggy (May 8, 2002)

dsisco said:


> The fans don't run once the engine is off,


Hi, Fans won't run unless coolant temp is 100 ish & you don't know yet whether coolant temp sensor Code 49 is giving the correct reading.
Fans are controlled by a thermal switch in rad, not by Code 49.
Hoggy.


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## 3TT3 (Aug 30, 2014)

Hoggy said:


> dsisco said:
> 
> 
> > The fans don't run once the engine is off,
> ...


Ive had a little trouble with mine up until the last 2 weeks or so,now fingers xed its as it should be .

Fans will run with the engine turned off,just like my by now 40 year old audi 80 used to  if the coolant is hot enough.

Im not talking about the "run on" pump to prevent a red hot turbo turning the oil to sticky carbon thing,but just if coolant is 100+ as Hoggy says the fans will run on with engine off.
Heres the thing tho..,its possible(I dont know) that if the coolant temp sensor that feeds the dash,ecu and 49c code is incorrect there may be an overide which shuts off the fans if the coolant temp sensor shows like 98c or less at engine switch off , even if that is incorrect.


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## dsisco (Jun 17, 2015)

checked my sensor the replaced, last month, the switch looks to be coloured blue & not green,

gonna change it today & see what happens, if not ill try the fan control module


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## Toad78 (Nov 20, 2014)

Hi, Any joy with fixing the problem?
I have the same issue but I bought a meat thermometer checked coolant temp against code 49 and I'm about 20deg higher on the code 49 than then the thermometer, replaced coolant temp sensor (Oem) and the problem is still there. The only thing left I think is the thermostat, does anyone know if it's ok to run without one to try?

Cheers in advance.


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## Hoggy (May 8, 2002)

Toad78 said:


> Hi, Any joy with fixing the problem?
> I have the same issue but I bought a meat thermometer checked coolant temp against code 49 and I'm about 20deg higher on the code 49 than then the thermometer, replaced coolant temp sensor (Oem) and the problem is still there. The only thing left I think is the thermostat, does anyone know if it's ok to run without one to try?
> 
> Cheers in advance.


Hi, What were the 2 temps @ thermometer & Code 49 ?
You can run without stat if you wish, as a test.
Hoggy.


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## Toad78 (Nov 20, 2014)

Hi Hoggy, on code 49 it was reading 104 and the thermometer was reading around 88.


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## Hoggy (May 8, 2002)

Toad78 said:


> Hi Hoggy, on code 49 it was reading 104 and the thermometer was reading around 88.


Hi, Was 104 recorded when reservoir car was off as it could only be 104 while pressurised, so if cap was off that 104 is false.
Hoggy.


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## Toad78 (Nov 20, 2014)

I have ran the car without the thermostat and it seems to run like it should, my question is could I run through the summer without one?


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## Hoggy (May 8, 2002)

Hi Toad, It will take longer to warm up & will probably never reach designed running temp unless left idling, so will run rich, not good for the engine or wallet. I'm assuming you are in the UK & not in a high temperature climate country.
Hoggy.


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## Toad78 (Nov 20, 2014)

Hi Hoggy, stay in Scotland so not exactly hot I'll grab another thermostat tomorrow. Thanks for your help.

Paul


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## Hoggy (May 8, 2002)

Toad78 said:


> Hi Hoggy, stay in Scotland so not exactly hot I'll grab another thermostat tomorrow. Thanks for your help.
> 
> Paul


Hi, Make sure it's OEM & an 87 degree stat. 2002 onwards an 82 degree stat was fitted, but If cooling system O.K. an 87 degree stat shouldn't cause any over heat probs & with the Scottish climate should help it warm up much quicker. 
Hoggy.


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## Toad78 (Nov 20, 2014)

Hi, well I replace the thermostat this morning and the problem has risen again.
Any thoughts most welcome


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## Hoggy (May 8, 2002)

Toad78 said:


> Hi, well I replace the thermostat this morning and the problem has risen again.
> Any thoughts most welcome


Hi, What was the coolant temp while driving normally,? not stationary.
Hoggy.


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## dsisco (Jun 17, 2015)

Dash said:


> If you've done the sensor recently, I can't see why changing it again would help.
> 
> My themostat wasn't working right when I got my car, and I think it's gone again 5-6 years later. But, my temperature is going the other way (both times), and the car can't maintain temperature.
> 
> Do the radiator fans come on when you've stopped and it's warm? They'll continue to run when the engine is off so it's easy to hear if they are going.


you were correct, changed sensor with a brand new one from AUDI, nothing changed ,
also ive noticed the radiator fans only come on when the heater/fan is turned on to max setting, if i leave the climate control in econ, the car heats up

they dont seem to turn on once the temp gets to 103c according to the 49c reading, also fans def dont run when the car is switched off no matter how hot, temp got up to 109c,

any ideas? maybe change fan module under the battery? or you think its the thermostat?


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## Hoggy (May 8, 2002)

Hi Dsisco, Thermostat only controls the coolant temp, the thermal switch in radiator via fan control module controls when fans cut-in, & the fans reduce the temps once it gets > 100 ish.
Do the fans run if Fuse 16 pulled ?
Hoggy.


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## 3TT3 (Aug 30, 2014)

dsisco said:


> Dash said:
> 
> 
> > If you've done the sensor recently, I can't see why changing it again would help.
> ...


I dont know what the module controls exactly.
Wot I know
1.the only way on mine to get the 49c readout with fans off is turn a/c on, mine on 18c then turn on econ then go for 49c readout.
2.I disregard the centre dash thing, altho it seems accurate within its damping range.
3.fans on around 100..temp rises to 102 then starts to go down. Temp hits 98 fans go off then cycle starts again.
If I turn off the engine with say temp showing 102 the fans will keep running.
4.Theres something about the two temp sensors/switches and turbo water jacket being in one circuit.. etc etc.I dont know exactly.

5.My old..yeh very old audi 80 I had to turn the heater on full and heater fan up to full to cool it down/ get temp gauge out of the red in traffic on a hot day. Very uncomfortable having heater matrix on as a radiator on a hot day!
With that .. it was actually crud in the cooling system,like limescale+ the switch was no longer accurate+ thermostat was replaced,took me awhile to sort.
I dont know how it works on the TT..but there must be some kind of valve to allow hot water into a "heater radiator", maybe there is some problem there.

The old audi 80 when fixed, would have rad fan "run on" even with engine turned off. My present renault 1.5 dci also has rad fan run on, when it gets very hot, after engine turn off.

My TT now has fan run on after engine turn off(in addition to electric secondary water pump, that seems to go on for ever  )..makes you reluctant to even just move the car.

nb: I had the 82c thermostat put in the TT.. I dont know if thats relevant or not


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## Hoggy (May 8, 2002)

Hi Joe, Nothing simple in the TT, even the coolant temp indication in a different position to the fan control thermal switch.
No flow through rad because of closed stat or faulty pump, so thermal switch may not detect high temp to switch fans, but coolant temp sensor register high temp because of it's different position, doesn't make sense.
"Vorsprung durch Technik" 
Hoggy.


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## dsisco (Jun 17, 2015)

Hoggy said:


> Hi Dsisco, Thermostat only controls the coolant temp, the thermal switch in radiator via fan control module controls when fans cut-in, & the fans reduce the temps once it gets > 100 ish.
> Do the fans run if Fuse 16 pulled ?
> Hoggy.


I can try, where is this fuse 16 located? If I pull will fan run constantly? Regardless of temp, ?


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## Hoggy (May 8, 2002)

dsisco said:


> Hoggy said:
> 
> 
> > Hi Dsisco, Thermostat only controls the coolant temp, the thermal switch in radiator via fan control module controls when fans cut-in, & the fans reduce the temps once it gets > 100 ish.
> ...


Hi, drivers side, remove end of dash.
Hoggy.


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## dsisco (Jun 17, 2015)

Hoggy said:


> dsisco said:
> 
> 
> > Hoggy said:
> ...


thanks for the quick reply, pulled fuse no change,

ran the car again, the fans dont come on above 100c, only when heat/ac is on, if i leave on econ the car heats up to 100c+

The only way I can get the car to cool is by having the heat on max hi & full fan,

Thoughts?


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## maltloaf (May 8, 2015)

Hi,

If switching the air con on is causing the fans to run then the fans are ok, the fan supply is ok, the fan control module is ok.

I would be testing/suspecting the thermoswitch in the end of the rad (very near the fcm on my 180)

You can short a couple of pins and if it runs it proves all of the wiring from the battery all the way to the fans and would tell you it's definitely the thermoswitch.


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## Abrazagar (Jan 7, 2022)

dsisco said:


> As per title, I have just purchased a MK1 225Q,
> 
> on the way home on the motorway I noticed the temp go past 90 on the dash to about 1/2 way to the next line,
> 
> ...


So I know I'm 14 years late, but i want to put this reply here for anyone else experiencing this issue currently. I've been having a similar issue with my 2001 Mk1 TT 180. Like most, i changed sensors, t-stat, flushed coolant, burped system, etc, but coolant temps still sat stable between 104-110 C.. an Audi/VW specialist told me that temp is not cause for concern, but I knew it was higher than the car _should_ run according to factory specs. (My car is stock btw). I believe said mechanic because i drove the car 600 round trip miles with no issue at all. Anyway, I decided to change my radiator and saw an immediate difference. While driving, temps fluctuated on my 49c menu between 92-98 (i believe this type of fluctuation is normal during driving conditions-hills, acceleration, engine braking, etc). At idle, it gets up to around 103 and sits there. Fans cut on and keeps the temp between 98-103ish. (OBD scanner actually showed a slightly lower temp than the 49c menu) I'm perfectly happy with these temps, (92-103C/190-217F) as opposed to the previous 103-110c that it showed before. so do consider replacing your radiator if you're having coolant temp issues. Especially if you don't know what coolant the car has been running...

TL;DR : coolant temps getting high? don't neglect your radiator. Over time they can get clogged/corroded and reduce coolant flow (which can bring up false symptoms of a faulty thermostat as well) Go with quality or OEM brands. I got a Behr Mahle radiator from FCP euro for like 160 USD. Everything bolted right up and it seems like my problem is fixed so far.

-Abrazagar


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