intermittent fluctuating temp gauge

[b3nny]

Hi,

Issue is on a late 59 plate 2.0l tdi 143.

I've done a search which and one post said that Audi says this is normal?

I replaced the temp sensor at the weekend to rule this out but is still fluctuating, it seems to be worse on cold days, I'm getting nice warm air through the blowers within a mile, the temp gauge will reach 90 but if I slow down or come to a stand still shortly after it getting to 90 the gauge falls pretty rapidly yet if the gauge has been at 90 for a while it seems to hold its temperature.

I went for a about a 10 mile drive last night and the top rad hose was still cold although the gauge was sat at 90.

Is it possible for the engine to get to temp and hold intermittently with the stat removed? I'm concenrned the previous owner my have removed it to mask and underlying problem as I've only had the car 6 weeks.
intermittent fluctuating
ig

 

[desertstorm]

It's a winter thing and it's normal. The diesel engine is very thermally efficient so doesn't produce that much waste heat unlike a petrol. The action of warming up the interior of the car especially when it's cold takes more heat from the engine than it's producing especially when it's idling so the engine cools . when you have been driving a while evrything has warmed up nicely and is hot so the temperature doesn't vary as much.
Also the temperature gauge tells porkys to stop drivers fretting about the temperature.
It is configured to read 90 when the engine is upto temperature.
Thats why pretty much any modern VAG car you go in the gauge suits at 90 through out the year when it's warmed up.
If you actually look at the engine temperature by the time it gets to 80 the gauge will be showing 90 and when it's at 100 it will still show 90. Thus there is not the amount of movement you used to have on a temperature gauge on older cars.
When the car is first warming up and it hits 80 and you stop a small drop in temperature gives you quite a large drop in gauge position. when it's warmed up at 90 degrees it could drop 10 degrees and still show 90.
Hope this makes sense, All of this is a lot worse with something like the 3.0 TDI I have, as it's such a big piece of iron it takes a long time to get warmed up,but the supplementary electric heater makes the heater work well.
If it had no stat it wouldn't make it to 90 at all this time of the year. Is the the first diesel you have owned ?

Karl.

 

[b3nny]

I kind of thought that regarding the stat as I had a kit car with no stat and that never reached temp until I installed one.

Makes sense being a winter thing though as it only does it on cold days.

No my last car was a b6 passat 2.0l tdi, can't say I noticed it on that maybe I've been more attentive with this one lol.

So my smashed to bits knuckles and bad back plus the price of a new sensor was actually nothing to worry about and is perfectly normal? What about the top rad hose being cold?

 

[desertstorm]

Top hose will only get hot when there is flow to the radiator. This only happens when the stat opens, and stat opening temperatures are hotter on newer cars than they used to be, part of the fuel efficiency thing.
The stat is not actually opening. If you were to get it on the motorway and give it a good run at 80mph and get the engine to do some work it would open.

 

[b3nny]

All makes sense and has out my mind at rest.

O well the car had a new temp sensor out of it not a bad thing.

 

[Zafi]

This was confirmed the the Audi dealer today as I thought my B8.5 had a thermostat fault.
They showed me an Audi document which explained that at ambient temperatures of less than 5 degrees the engine can take forever to get to 90 at low engine speeds. I do a 30 mile cross country run at maximum 60 and it was not reaching 90. They said it's normal. The engine is OK running at 50 to 90, thats why it has the Aux heater.

 

[b3nny]

Perfect, thanks for that at least it's nothing to worry about.

 

[phils4s]

This was confirmed the the Audi dealer today as I thought my B8.5 had a thermostat fault.
They showed me an Audi document which explained that at ambient temperatures of less than 5 degrees the engine can take forever to get to 90 at low engine speeds. I do a 30 mile cross country run at maximum 60 and it was not reaching 90. They said it's normal. The engine is OK running at 50 to 90, thats why it has the Aux heater.

This is interesting because my 2013 A4 2.0 TDi 177 takes a long time to heat up according to the temperature gauge & I thought there may have been a problem but it seems they are all like this. The heater starts to give out heat reasonably quickly but I understand they are fitted with an electric heater to help with this but the auxiliary heater you mentioned is only fitted as an option. Our old X5 had one & it certainly helped to get the engine up to temperature quicker.

 

[Zafi]

Its not like a auxiliary pre heater that work on a timer to heat the car before you start the engine, it only works when the engine is running.
The heater has to be on auto and set to 22 degrees or higher.
I'll try get the bulletin from the dealer.

 

[vw754]

mine goes to 90 then sits there,and it takes a bit longer get to 90 as its colder now,but 10 minutes into my journey its on 90

 

[Zafi]

mine goes to 90 then sits there,and it takes a bit longer get to 90 as its colder now,but 10 minutes into my journey its on 90

But yours is a B8, I think this only applies to B8.5

 

[vw754]

i was rep;ying to b3nny who has stated his car is a b8 59 plate

 

[Zafi]

Oh, yeah! Good call... my 2010 B8 never did it so I wonder when they changed??

 

[phils4s]

Its not like a auxiliary pre heater that work on a timer to heat the car before you start the engine, it only works when the engine is running.
The heater has to be on auto and set to 22 degrees or higher.
I'll try get the bulletin from the dealer.

If you could, that would be good. I didn't know about the 22 degrees & auto thing.

 

[Leslie Ashe]

I got the same reply from my dealer - see thread started today. Mine is petrol TFSI not diesel and until a month ago the gauge sat at 90. Now it fluctuates which makes a bit of a nonsense of what the dealer says.