Is my mpg meant to be this low?

[N44HXM]

Hi all,

Recently just bought a new GTi Mk5, extremely happy upgrading from a Aygo after 3 years.

The thing is the mpg is currently so low, around 23 which is a mix of dual carriage way and some normal roads.

My temperature is quite low, takes a while to get to 90 but could this be due to the weather in London?

Just came home after a 15 minutes drive, so a couple minutes of 30 mph mile roads, then I was doing a constant 50 on the dual carriage way till coming home. After 15 minutes of driving the car still was mostly around 70ish and once I got home it got to around 75/80. Is this something to be concerned over?

Thanks!

 

[1131]

Lots of things can contribute to poor gas mileage. Proper tire inflation. Rubbing brake pads. But start with fresh spark plugs. Yes, it can take a while for the coolant to get to 90. That part looks normal. If you're very concerned about it, I guess you could replace the thermostat, but that's a non-trivial repair since it's pretty deeply buried. I'd leave well enough alone.

 

[N44HXM]

Yeah I think the spark plugs are quite old to be honest, don't think the previous owner changed them for a while. Will get them all changed and see if there's an improvement.

 

[ROH ECHT]

The thing is the mpg is currently so low, around 23... Is this something to be concerned over?

Yes it is. The temp issue is likely the thermostat. Quite a few MK5's have begun to see the thermo's fail. Mine just began with a P2181 code and the temp gets near normal and drops before reaching normal(because the thermo is opening prematurely)...then takes a long time to reach normal. Temps do affect optimal running and can affect its mpg because it will run richer when a thermostat is stuck open or opens too soon. For this reason, I wouldn't begin addressing the mpg until you fix the thermo issue.

Then after you install a new thermo, regarding the mileage, I would find someone that could help you to read fuel trims just to make sure all else is OK. So, to eliminate whether or not it is a leak issue first. Fuel trim additive's live data, or short term fuel trim, can tell you if it has a leak in the vacuum system or air inlet system. Fuel trim multiplicative data can tell you if it is an ignition issue.

Have you had the stored codes looked at?

 

[GTI's]

In stock form these car are not mileage masters, depending if DSG vs Manual. This is from the US EPA for mileage efficiency for a '07 GTI

Manual https://fueleconomy.gov/feg/compareMPG.shtml#id=22779

DSG https://fueleconomy.gov/feg/comparempg.shtml?words=#id=22780

As you can see you are not that far off from the combined numbers, perhaps you can look up the Euro mileage figures for your GTI.

If you have a scan tool use it to check for codes and to also log the Temp sensors from a clod start and that will give you a better idea if senor issue or the thermostat is staying open.