Losing temp while stationary...

palfy86

palfy86

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As the title really, was waiting for a mate this morning, car was at 90 degrees when i pulled up but while i was waiting with the engine on and interior heating going, the temp gauge was dropping....

Is this normal? outside temp was -1 on the dis.

never really noticed this before but because i was waiting so long 10-15 mins it caught my eye

Many thanks in advance.
 
The thermostat may be stuck open. There is another potential problem which is that the radiator fan(s) may be running all the time - I've just had this. On a cold start, the electric fan would run at full bore, and usually continue to do so, irrespective of engine temp. The cause turned out to be the temperature sender at the back of the block, by the bulkhead.

I only have an electric rad fan - depending on engine type, it seems some have two fans, diesels I believe, one being a viscous fan. If the car has a viscous fan, the coupling may have seized, so also worth a look see. If it is working properly, you should be able to stop it by gently (and carefully) holding a rolled up paper / cardboard to it.

Changing the sensor seems also to have fixed an irritating fault I'd never been able to track down (nor indeed could Audi). While cold, the throttle response wasn't all the smooth for the first mile or so - and when warm there was a minor flat spot, or "fluffing / hesitation" at just over 2,000 revs. The new sender seems to have fixed those too. I assume the ecu wasn't getting good data on temperature.

The car is a 53 plated 2.0 fsi. I believe our cars all have two temperature sensors - one at the bottom of the rad, the other (the main one) at the back of the block.
 
Mike.M its the 1.9 tdi avf engine.

Mike.B ive never noticed the fans running all the time though. and ive already replaced the coolant temp sensor roughly 2 years ago with a genuine one.
 
To me it sounds like the thermostat it stuck open as once at temp it should stick there
 
Yeah mike i was thinking this maybe the case. Ill have to see about getting it changed.
 
This happened to me last year and found the housing guide clip had broken off and got stuck in the thermostat as it was closing I guess.....the car was running cool all the time and never stayed at it temp.

Took the stat out and put in a pan of hot water to open it fully and remove the object.....replaced and has been fine ever since. Once it get to 90, it stays there regardless.

I was lucky the stat caught the clip and the engine never got hot enough to release it
 
yeah very lucky from sounds of it Mike. Well this could be an ideal opportunity to flush the whole system etc at least.
 
In the summer my temp gauge sits on 90 & doesn't budge but in the winter months my AVF acts exactly the same as yours, & couple of TDI Bora's i've owned did it too. All had new VAG stats fitted at one time or another during my ownership, & I think you'll find that if you turn the heater off it'll start to move back to 90c. Theory I have is cold air being drawn across the heater matrix cools the coolant enough that at idle the temp drops.
 
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Normal on a diesel, if the thermostat was stuck open it never would have got near 90 degress. When idling the engine uses very little fuel so produces little heat. The cooling effect of the heater warming the inside of the car takes more heat than the engine produces.
This is why diesels take so long to warm up in the winter as well, the thermal efficiency is a lot higher than a petrol engine so they just don't produce the heat.

Karl.
 
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I'm forever loosing my Temp whilst stationary, I ****** hate Jams. Oh excuse me, I misread the title I'll be in the corner getting my Jacket >>>>>>>>>>>
 
audi upgrades
@desertstorm and pauldazzle so are we saying its perfectly normal for this to happen?

the car doesn't struggle to hit 90 degrees at all and will sit there all day long while driving.
 
Yes it's normal this time of the year. I owned a 1.9 130 Passat for over 7 years and used to see the same every winter.
 
so running the car in a morning to "warm" the cabin up would be pretty pointless in this respect then?
 
The TDI's have a supplementary electric heater that gives you some heat when it's really cold.my 2002 Passat had one so I suspect yours will have the same thing.
They look similar to this

http://www.ebay.co.uk/itm/AUDI-A4-B...arts_Vehicles_CarParts_SM&hash=item5d4f8f9781

This is the reason you get vaguely warm air out of the vents just after you start the engine. The ECU turns the heater on after the glow plugs have gone off. These things take about 50-60A when on full, so load up the alternator a bit which means the engine has too work a little harder, another reason fuel economy drops in the winter.

Karl.
 
Good info there......still never noticed mine drop, apart fro when it was stuck open, but then I may not be still in traffic long enough to notice anything.
 
Well Gents thanks again for all the help and info on this one, sounds like nothing to be concerned about, may still change the stat just for peace of mind :thumbs up:
 
If you change the stat use a genuine VAG part. Aftermarket stats haven't got a good reputation for working properly on VAG cars.
 
My 2.5tdi has never done this and I still say if you have the right stat it will maintain the correct temp.Can you see the Germans accepting an engine that doesn't with their climate
 
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Mike B said:
My 2.5tdi has never done this and I still say if you have the right stat it will maintain the correct temp.Can you see the Germans accepting an engine that doesn't with their climate
Click to expand...

Replaced the stat in my 1.9tdi awx last year with a genuine one and even in the current cold mornings it kicks out warm air pretty quickly. Once it reaches 90 it stays there. If I'm stationary for a bit it may drop to 80 but tbh don't really notice it.
 
Thermostat - - every diesel I've ever had would hold 90 when idling. In fact, every car I've ever had never lost temp sitting idling.
 
The 2.5 TDI is not a 1.9 TDI is it. This is perfectly normal for a 1.9TDI and thats why they have the auxillary electric heaters. There is no way you would get ueseable heat out of the car after 30 seconds running when it's below zero.
The themperature gauges on modern VAG cars are electronic and are "fiddled" so the owners don't keep thinking they have an issue with the engine because it's a bit cooler or a bit hotter.
The temperature gauge pretty much always reads 90 all year round, but if you actually look at the temperature being seen by the instrument cluster anything over about 75-78 degrees will result in the gauge showing 90 and the temp has to get over 100 degrees before it starts moving up above 90.
Thats why a lot have cars have ditched temperature gauges. The wifes Yaris has a blue light when it's cold and a red one comes on if it's too hot. The blue one goes out at 50 degrees as I have had my torque Pro connected to it when it has been warming up.
If you were sitting in your 2.5 TDI with the heater blasting away at idle the engine temperature would drop but you won't see any movement on the gauge unless it goes down below about 78.
The 2.5 TDI will be producing a lot more waste heat than the 1.9 TDI.

Karl.
 
Don't use the auxiliary heater, no need. Within a few miles I have warm air (just)! Not sure where 30 seconds came from.
 
So this is a characteristic of the 1.9 or at least some of them, but not diesels in general though I don't understand why the 2.5 creates much more waste heat than a 1.9.Doesnt overheat in summer or seem to need the fan on much.Still think the germans wouldn't put up with a car that didn't have a decent heater
 
It's probably your coolant temp sensor. Mine was the same, up to 90 degrees no bother, but would drop when sat in traffic. Warranty claim for the thermostat, which was a bonus having the 2.5tdi as the belts need to come off. After all of that, symptoms still the same, changed the sensor and job done. No more dropping of temperature.
 
Changed my stat a few years ago as the thing would not hit 90 on the temp unless you really pulled the ears off it, and dropped when in traffic again, and that wasn't during the winter.
The gap in the stat was so small when cold you could barely see through it, but enough to over cool the engine.
As Karl says, the high injection pressure and atomisation of the diesel will actually cool the cylinders down at idle, so it wont really heat up much when started from cold and left to idle..

I only have a 5 mile drive to work, gauge just hits 90 deg on this run when sub zero, you can feel its not properly warmed up although the gauge reads 90 deg, still say it takes a good 20 - 30 miles to warm a car properly, transmission etc..
 
Have never sat long enough in the winter to notice it drop, but when I've been sitting at idle the temp gauge never rises until I drive. So in the cold and long enough stationary I could well imagine it to drop a little.
 
Hi all! I have problems with coolant temperature on my B8 2.0tdi 105kW. Last year I changed thermostat with OEM one because of temperature wasnt sitting on 90 degrees and falling down while driving and on idle. After that the situation was same temperature varies and no "lock" on 90. I pressumed that the problem is in temperature sensor and I changed it month a go but no luck. Yesterday I put a new aftermarket thermostat FEBI which is opening on 83 degrees but now the situation is even worse with coolant temperature not crossing 70 degrees and heating not working well even if I set it to HI. It was +5 degrees above zero this morning when I was driving to my job and coolant temp scale not exceeded 60 degrees. I have vcds diagnostic tool no errors on the engine except one glow plug on cylinder 1. HVAC module no errors. I tested scales on instrument cluster all fine. Coolant temperature reading is same on vcds and instrument cluster. I dont know what to do anymore, please help! Sorry for bad english. Greetings from Croatia!
 
Of course I will put OEM thermostat back on because it is obviously working better than aftermarket.
 
I'm getting similar readings.
Driving is fine and brings the temp gauge to 90 after 15-20 minutes. But then, it drops every time when stationary/idle on traffic light or something.
Goes back up again once off.

Had a stat changed about a month ago and it was fine, untill yesterday.
Noticed also coolant level dropped.
Been top it up after stat job, 2-3 weeks ago. Now its right at the min level and was above max, then.
How many time the stat can go?
Can it be temp sensor?
 
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