Thermostat

[Jono8]

The other day, i noticed my mpg was perhaps 1-2mpg lower than normal for no apparant reason.

I didnt think much of it, but i know a possible cause of this is a dodgy thermostat ( i.e. car not staying at full working temperature).

The car does warm up within what i believe to be a normal time and the temp guage goes to bag in the centre within 6/7 minutes or 2 miles, sometimes sooner and the guage will be in the centre the whole time im driving....EXCEPT, yesterday i noticed that on the long (1 mile+) steep downhill stretch on my commute where i am off throttle for all of it the guage dropped slightly (moved about 2-3mm to the left of the centre). When at the bottom, and back on the throttle the guage will go back to the centre and stay there.

Now, from my research, this indicates the thermostat is getting stuck open/partially open. Correct?

 

[Jono8]

Hm. The same mixed responses that i am getting from looking over the web

I was of the understanding that once up to temperature, a thermostat should keep the car at the correct operating temperature regardless of what is happening?

 

[Jono8]

So you are saying that as long as it warms up ok and only drops a bit when off throttle/coasting in gear for a long period everything is ok?

Ive tested and last two times i have been up the car has got up to temperature within 5/6 minutes and 1.5-2 miles

 

[Jono8]

OK. I won't change it for now then but will monitor the situation.

 

[Jono8]

Tons of other normal things can cause an mpg drop, old oil/filter, air filter, plugs, poor injectors, tyre pressure, bad alignment

I know, but i just though that this dropping of temperature slighlty when coasting downhill for a while might be indicitive of something.

The consesus in here seems to be that it isnt and this is normal.

 

[Jono8]

Hm, well i don't know what to think. : /

 

[Jono8]

It may not be normal but WHAT CAR IS IT?

Octavia VRS II. 2.0TFSI

 

[Jono8]

When mine went it wouldn't go above 1/4 way up the scale, remember the weather is colder, i've noticed a 1-2 mpg drop since the cooler weather has snuck in, takes longer to warm the engine up which means it's running rich for longer. And you're using the heaters which take heat from the coolant.

Yes, i am running the heaters from the get go. Heaters do start chucking warm air after a few minutes. Car warms up to the middle mark on the guage within 10 minutes at the absolute maxium, normally less (say 6 minutes).

I have so far only seen the guage drop slightly coasting downhill. Everything i read on the internet about it is conflicting. Some say that if the temp guage ever drops after the car has got up to temperature, it means the thermostat is sticking open, some say it is completely normal

 

[Jono8]

get it connected up to vagcom and youll see the temp being reported to the ecu

then youll know what the coolant temp is rather than trying to guess what the damped gauge is telling you

I dont have easy access to vag-com but will try and get it read soon by my local specialist.

 

[Jono8]

if you have an android phone, an app called torque plus a £10 obd dongle will give you a very quick easy way to monitor things like this too

Oh right, thats sounds useful. Do you have a link to a guide on how to use it/what dongle to buy?

 

[Jono8]

the app
https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en

the dongle
http://www.amazon.co.uk/gp/product/...m=A3P5ROKL5A1OLE&pf_rd_r=1GSDGYQAQJ8JND6MBWAC

then just keep clicking buttons until it work

you get 5 pages for live data which you can put all sorts of gauges on

i have one page for coolant and intake temperatures plus voltage


then boost and maf air flow

then throttle/ignition timing/revs

then a page for lambda activity

all very boring/geeky stuff

Thanks.

I'll get one fof those dongles and have a play.

I presume it isnt going to do any damage to the engine if the thermostat is a little dodgy for a bit? I mean the temp needle is bang on centre at all times apart from when i am coasting down this hill for ages : /.

 

[Jono8]

The temp should not move from 90c once up to temp, the cluster has it heavily weighted. Mine never moved from 90c even when it was indicating -26c outside.

If your vRS has climate control you can get it to display the actual coolant temp. Push the econ button and the vent button with the arrow pointing up at the same time, you then use the left dial to move the left display to 19 the middle dial to get 19.2 on the left display the right display will then show the actual coolant temp. For reference mine with an outside temp of 2c sat at 79c, even off the throttle going down a fairly large hill it only dropped to 78c.

The temperature hasn't dropped enough to knock 1-2mpg off my consumption I find it needs to be in constant negative temperatures to notice a drop.

Oh yes i forgot the climate control can show all sorts of readings, thanks! I will do this and monitor the temperature on my next journey to work and see what is happening.

 

[Jono8]

The temperature should not move from 90c once up to temp, the cluster has it heavily weighted. Mine never moved from 90c even when it was indicating -26c outside.

If your vRS has climate control you can get it to display the actual coolant temp. Push the econ button and the vent button with the arrow pointing up at the same time, you then use the left dial to move the left display to 19 the middle dial to get 19.2 on the left display the right display will then show the actual coolant temp. For reference mine with an outside temp of 2c sat at 79c, even off the throttle going down a fairly large hill it only dropped to 78c.

The temperature hasn't dropped enough to knock 1-2mpg off my consumption I find it needs to be in constant negative temperatures to notice a drop. The climate control also doesn't turn up the fans/heat until the coolant is at a reasonable temperature.

Ok, so i have driven home with 19 - 2 selected on the climate control and it read 76~ all the way. Went up to 78 sitting in traffic, down to 75 ( lowest i saw it go) when going at speed.

I will have to test the downhill section tomorrow on my way to work.

That is too low right? I though the correct operating temperature was 90 degrees?

N.B. Temp guage was showing to be bang in the middle the whole way home.

When you say at a stand still at 2 degrees ambient it was 79 degrees, did you mean 89?

 

[Jono8]

Mine was at 79c today for most of my journey, I had a couple of bikes on the roof going into a headwind and it went up to 82c. The gauge sits at 90c for I assume no other reason than it is in the middle of the gauge.

Hm, maybe mines a bit low then, but doesnt seem drastically lower than yours. I let it idle for 5 minutes and it just seemd to sit at 78 degrees. Warm up to middle of the guage temperature still never takes longer than 10 minutes.

I understand the stat on this engine is a pain to do and will be 2-3 hours of labour so don't want to part with the best part of £200 for no reason.

 

[Jono8]

Now we know what car it is I can tell you this is not normal.

VAG coolant temp gauges do not give a direct readout, in fact the gauge will read as 90 over a range of temps. The gauge should read 90 consistently once upto temp, variances around normal operating temp will not be visible on the dashboard, it should be stuck at 90. If its stays below 90 on a decent run or not getting to 90 you most likely have a thermostat that's stuck partially open, the other thing to check is the coolant temp sensor, it's not likely to be this but this is much cheaper and a DIY job so it's worth ruling out.

The guage on the dashboard does get to the 90mark in 10 minutes at the very maximum and stays there consistently. The only time it drops is coasting downhill in gear for over a mile. It never stays below 90 or doesnt get up to 90 on the dashboard.

As my earlier post says i have got the exact readings from the climate control computer and it varied bwteen 75-78 degrees the whole way home from work today. I will check to see what it goes down to when going down that hill on my way to work.

 

[Jono8]

Most thermostats open at 78°C So expect it to hover in this area.
The ECU will consider anything over 70° as normal running temp.

Everywhere i have been today it has moved between 75-78. No more, no less. It will be interesting to see how low it goes going down the hill tomorrow.

 

[Jono8]

Hm, interesting. so it is 10 degrees off basically? Does that mean it is not closing fully, or that the thermostat could be dodgy/ not opening at he right temperature somehow?

 

[Jono8]

opening too early it would seem

What would cause that?

 

[Jono8]

So stats can lose their ability to open at the correct temperature then yes?

Presumably, as it is already running at a low temperature ( although within an acceptable range for the temp guage on the dash to be where it should be), the downhill coasting part just tips it below the correct working range causing the slihgt drop of the needle. Does that sound plausible?

hm, looks like i might get it done soon then to be on the safe side.I can get the OEM VAG part for ~ £30 it seems. I will have to talk to my local VAG specialist to see how much they will charge me in labour to fit it.

 

[Jono8]

The view from the Audi TT forum is that coolant temp shouldn't vary much below 90. It can go up to 100 in traffic (then the fans kick in, as per usual), but it shouldn't go below 82. 82 is the lower threshold for a 90 reading on the temp gauge, and the stat is a 82 degree open one I think?


If you've got the tools, it's generally very easy to replace.

Hm odd. My climatronic display was giving 75-78 readings but the gauge was bang on centre.

With regards to it being easy to replace, i have read it is a bit of a bugger in these and the alternator needs removing to gain access to it. Not something i really fancy doing myself. I cant find a clear and good guide to do it anyway.