35MPG - Is there something wrong?

[Grant]

My car's average Mpg on a tank was usually around the 42mark, but recently I've seen it drop to around 35mpg. i've not changed anything on the car and all the fluid levels are fine. I also not noticed any lose in power or performance, nor has any warning lights come on. I have noticed though that the raditator is always stone cold and the temperature gauge very rarely rises over the minimum mark, even if I'm sat in traffic or drive it hard.

A guy at work suggested it could be some pipework which is leaking or the MAF sensor is faulty.

Should I go to the garage and ask them to look at it? Or is it just down to the cold weather?

Cheers

[Chris GB]

My car's average Mpg on a tank was usually around the 42mark' date=' but recently I've seen it drop to around 35mpg. i've not changed anything on the car and all the fluid levels are fine. I also not noticed any lose in power or performance, nor has any warning lights come on. I have noticed though that the raditator is always stone cold and the temperature gauge very rarely rises over the minimum mark, even if I'm sat in traffic or drive it hard.

A guy at work suggested it could be some pipework which is leaking or the MAF sensor is faulty.

Should I go to the garage and ask them to look at it? Or is it just down to the cold weather?

Cheers[/quote']

Could be a stuck theromastat (in the cooling system). If it stays open, the engine never gets to warm up and the fuel system will run the car rich as if on warm up cycle. This will account for the fuel consumption change.

Chris

[Grant]

Could be a stuck theromastat (in the cooling system). If it stays open' date=' the engine never gets to warm up and the fuel system will run the car rich as if on warm up cycle. This will account for the fuel consumption change.

Chris[/quote']

Cheers, would it be expensive to change myself or at the garage?

[WW_VRS]

Wouldnt have thought it would be too hard to change yourself, although there are probably some procedures to follow and all that, plus I've had the misfortune once of purchasing a brand new, non-working thermostat once (this is a bit rare but it can happen :( )

I'd give a few garages a buzz, as it's out of warranty anyway you should be able to get a pretty good price for the job

[Maffu]

I got 38mpg ona 25 mile commute the other day. I don't think I could have blamed a sensor for it though...*ahem*

How heavy is your right foot, dude?

[vrsfab]

If there's plenty of coolant in the system, then it sounds like the thermostat is stuck open. It should be an easy DIY job. I'm sure a techie will be along soon to tell you where it is.

[Fabia156]

Well.. i can barely do 30 MPG with my 1.4 16V Fabia.. but my foot can be very heavy sometimes lo.. but i think that 30 MPG is not that great for a 1.4

[SteVRs]

Hey Grant, are you doing shorter journeys or is anyone else driving your car at all?

Are your tyre pressures low or are you driving with A/C & lights where perhaps you weren't before?

[davidcollins01]

i've managed 28mpg average out of a 2.0 tdi

[chowy]

Before winter I was getting 47-48 mpg on varied roads. I now get 43-44 mpg which is what I usually expect during the winter months.

I would say that an 8 mpg change maybe a little excessive unless you've changed your driving style or route to work?

[devonutopia]

I get 45mpg still - 17s, sticky tyres, nicely over 200 bhp and not afraid to use it whenever I want. An 8mpg drop with no change in weather conditions, driving style and performance might mean its running a little off, and some sensor somewhere is perhaps making it dump more fuel in? Seen much more smoke?

[ScoobyChris]

As Jase mentioned, is it running more smokey than usual, as this could indicate it's overfuelling (dodgy MAF sensor?). Also what fuel are you using, are you doing short journies?

Chris

[JBS Auto Design]

Coolant temp sensor.

This will be making it think the engine is still cold.

So it will run rich.

Not expensive £20.00 ish punds.

On the Octavias you will find that they are 4 pin green 059919501a but just check with the dealers.

A doddle to fit too.

Sarah

[BigW]

Coolant temp sensor.

This will be making it think the engine is still cold.

So it will run rich.

Not expensive

[JBS Auto Design]

Hi

It does not all the time.

One way is to see that the guage is reading incorrectly.

It does not even bring up a fault code all the time.

They are very common.

You will find that all major garages have them in stock.

We have 2 perminently in stock.

It is not alot of money , easy to do and will not always be detected with VAG COM

I have had 3 in my little Felicia and that was detected by it being a little tricky to start when slightly warm.

So that could be another way to detect the problem.

Sarah

[HellFire]

I have managed 20 mpg on a 30 min trip before

My worst ever was a 5 minute stint after warming & cooling the engine properly which equated to 9 mpg.

For a minute I thought it was a diesel

On average though in city traffic (Leeds) I manage around 42-48 mpg, and 35 if i'm spirited.

[pbirkett]

Could be a phenomena called lead boot

[Johnwg]

Had a sudden drop in mpg in mine after a few months of ownership... turned out I had a nail in one of the rear tyres (only spotted when the tyre had gone right down after about 5 days) after a week of cheaking out

every other possibility.

I'd start by checking your tyre pressures and keeping an eye on them for a couple of days and take it from there.

[yashicamat]

I changed the thermostat on the B5 Passat and it was fairly straightforwards. You can check the thermostat by attatching it to some string and lowering it into some boiling water - if the inner part moves, then moves back again when you take it out, it's working.

You will need new coolant for a thermostat changed as you have to drain the coolant system.

By the way, I got a thermostat for the passat for £3.50 from a motor factors - can't see why a Furby thermostat should be any different.

[yaktrebor]

I've noticed my temperature reading in the dash doing strange things recently.

Normally it will gradualy build up temp until it gets to the normal (12 o'clock) position.

The last few days it gets to about 11 o'clock for a few miles, then goes back down to 10 o'clock for a few miles.

It dos this a few times and eventualy gets to 12 o'clock and stays :confused:

Is this the sensor? or is something else trying to tell me something?

[yashicamat]

yaktrebor: does the temp guage do this in relation to speed? A stuck thermostat can show normal engine temps at low speeds as the airflow over the radiator isn't sufficient to overcool the engine, but at higher speeds the temperature drops because of the high cooling.

If it's a lot more random than that, I'd be tempted to say that it's the coolant temp sensor.

[Grant]

Right a few more detials,

Nothing on the car has changed in the last few months, everthing is standard, except the PD160 inlet which has been fitted for 12mths. I have been regulally using normal Sainsbury's Diesel, and BP Ultimate as a one off (which showed no difference at all). I do the same route to work every day which is 13miles and about 50:50 motorway and urban, it usually takes 45mins in the morning and around 25 at night. I do have a heavy foot, but managed 42mpg regually on the same route and same driving style. There is one stretch of road which is a long steepish uphill run, before i could reach 105mph quite easily, but now I stuggle to reach and sustain 95. Finally I've not used the AC for a while because it has been too cold for it to work properly, and I've taken my sub box out which weighed around 60kgs which, in theory, should help.

I noticed this morning that if i turn the cabin temperature to minimum and turn the fan off the gauge will rise to around 1/4 in traffic, but drop again when moving.

Thanks for the discussion and help people, but I'll ring the garage tommorrow and ask them to check over the ECU for errors, and change the Thermostat.

Has anyone got a Thermostat change guide?

[alexst]

Could be fine, I get 32mpg in London, and 60 on Long journeys on Motorways doing about 80.