My cars started getting significantly worse mpg than when I got it i'm averaging like 40mpg everywhere where I would get 50 plus if i did more than 5 miles before and I'm getting worse economy according to the display in 6th gear on the motorway than 5th. Any ideas what to look for as a cause for it?

 

I got the car at 77k miles and its currently on 83500 miles and getting an oil change this week by me with new air and oil filters. I've noticed its not staying hot after getting upto temperature on the motorway then town driving so planning on changing the thermostat as well. I have noticed a wet spot behind the EGR valve and the screws around the turbo look a bit black so maybe leaking?

I've never had a turbo or diesel car before just BMWs so would appreciate any advice.

Fuel economy is a tricky one, so many variables.

 

The cold weather is a huge part of it, I currently get 40-45mpg with a mix of town/motorway driving, whereas in summer I can get 50-55mpg doing the same. (Mk3 2016)

If you are noticing changes in the temperature on the motorway it could well be a thermostat or faulty coolant temp sensor, it will also affect the warm-up period, so well worth changing

Have you noticed an increase in DPF regens? (presuming the car has one) 

 

I would get the car plugged into a diagnostic machine, just to check for codes and obtain some live data readings, there are members on here who could help with that depending on location.

 

 

 

8 hours ago, craycrayfrog said:

Any ideas what to look for as a cause for it?

The fuel tank. Not joking; you get worse mpg on Winter diesel than on Summer, and on E10 petrol/ethanol than E5.

You can get a better MPG on winter spec diesel with anti-waxing in it if it is nice and cool weather with nice dry cool roads and not short trips and not sitting de-icing etc.   It has not got a lower cetane.   But for years people have said it gives less energy.   Maybe some can use winter spec diesel after April in the UK and compare then with Summer spec and see for themselves. 

Check for binding brakes as well. Have a feel of each wheel for heat after a drive. This can have a massive effect on economy if they are binding.

 

Edit: Also check tyre pressures. In this cold weather they drop significantly, so check and top up as required.

Edited 17 January, 20224 yr by Golf-Fiend

7 hours ago, MATT0693 said:

Fuel economy is a tricky one, so many variables.

 

The cold weather is a huge part of it, I currently get 40-45mpg with a mix of town/motorway driving, whereas in summer I can get 50-55mpg doing the same. (Mk3 2016)

If you are noticing changes in the temperature on the motorway it could well be a thermostat or faulty coolant temp sensor, it will also affect the warm-up period, so well worth changing

Have you noticed an increase in DPF regens? (presuming the car has one) 

 

I would get the car plugged into a diagnostic machine, just to check for codes and obtain some live data readings, there are members on here who could help with that depending on location.

 

 

 

It's never had a DPF regen havent seen any lights and have had some extended motorway journeys though it only does a 12 mile motorway journey once a week with the rest being approx 3 miles and I've ran redex dpf.
I really expected a engine light but fair enough I'll try.

 

7 hours ago, KenONeill said:

The fuel tank. Not joking; you get worse mpg on Winter diesel than on Summer, and on E10 petrol/ethanol than E5.

I'm in the UK are you sure they change fuel its labelled as b7 at asda/tesco and theres a gulf locally. I didnt want to switch to shell but if its going to be significantly better?

 

5 hours ago, roottoot said:

You can get a better MPG on winter spec diesel with anti-waxing in it if it is nice and cool weather with nice dry cool roads and not short trips and not sitting de-icing etc.   It has not got a lower cetane.   But for years people have said it gives less energy.   Maybe some can use winter spec diesel after April in the UK and compare then with Summer spec and see for themselves. 

All code I'll use google to translate.

5 hours ago, Golf-Fiend said:

Check for binding brakes as well. Have a feel of each wheel for heat after a drive. This can have a massive effect on economy if they are binding.

 

Edit: Also check tyre pressures. In this cold weather they drop significantly, so check and top up as required.

I've had a check brake pad message on the display in wet weather and they were serviced in march with new pads by the dealer. Hopefully theres nothing up with the calipers.

1 minute ago, craycrayfrog said:

It's never had a DPF regen havent seen any lights and have had some extended motorway journeys though it only does a 12 mile motorway journey once a week with the rest being approx 3 miles and I've ran redex dpf.
I really expected a engine light but fair enough I'll try.

 

The car will do a passive regen when the exhaust temperatures are 400'c - 500'c, this won't put a light on the dash. 
If the car isn't able to this, the engine management system will step in and inject fuel to increase the DPF temps to burn off the soot without putting a light on the dash. 
When the DPF can't complete the cycle and it gets too full, it will put the DPF light on so you can perform a 'regeneration drive cycle' until it clears.

 

My car completes one every 300-400 miles usually, if I do a lot of short trips and have supermarket fuel, it can be as little as 170miles. If you have ever got out of the car and heard the cooling fans running still, it could be because you have interrupted the regen cycle. It is worth downloading VAG DPF, it is less than £5 on the app store and connects to a Bluetooth OBD adapter, it gives you live DPF data and shows you how much life it has before replacement. You can then also use the adaptor to read fault codes etc through either free or paid apps.

 

@craycrayfrog

Winter spec diesel is delivered to filling stations in Scotland & the North of England from Mid October and then further south soon after until the end of March.

Nothing to do with Brands of Diesel.  

 

Super market diesel be it on a pump with TESCO, ASDA, MORRISON, SAINSBURY etc is no different from any other Regular Diesel that comes out a pump with Shell, ESSO, BP, Gulf, Texaco or anything else.

 

If you want Premium Shell V-Power or ESSO, BP etc with more additives then that costs more than their REGULAR DIESEL / DERV that much of UK diesel vehicles run on and more than half of that is retailed to car  drivers from Supermarket Filling stations.

Edited 17 January, 20224 yr by roottoot

1 hour ago, MATT0693 said:

 

The car will do a passive regen when the exhaust temperatures are 400'c - 500'c, this won't put a light on the dash. 
If the car isn't able to this, the engine management system will step in and inject fuel to increase the DPF temps to burn off the soot without putting a light on the dash. 
When the DPF can't complete the cycle and it gets too full, it will put the DPF light on so you can perform a 'regeneration drive cycle' until it clears.

 

My car completes one every 300-400 miles usually, if I do a lot of short trips and have supermarket fuel, it can be as little as 170miles. If you have ever got out of the car and heard the cooling fans running still, it could be because you have interrupted the regen cycle. It is worth downloading VAG DPF, it is less than £5 on the app store and connects to a Bluetooth OBD adapter, it gives you live DPF data and shows you how much life it has before replacement. You can then also use the adaptor to read fault codes etc through either free or paid apps.

 

I have the vag software somewhere just havent tried to use it. The stuff you're recommending is probably easier as i have a bluetooth ob

58 minutes ago, roottoot said:

@craycrayfrog

 

 than their REGULAR DIESEL / DERV that much of UK diesel vehicles run on and more than half of that is retailed to car  drivers from Supermarket Filling stations.

I dont know what you mean by that.

 

I didn't have a clue I was on winter diesel tbh I didnt think NW of england was cold enough for that.

People in your area might fuel up and drive where it is colder.

Lots of cars in garages & dealerships, hire places, auctions and other places are sitting now with old / summer spec diesel in now.

 

It is what is distributed every winter in the UK and gives protection to minus 15*oC. 

That is be it Regular Diesel, Premium Diesel or Red Diesel. 

(There is also Winter Spec Petrol / Gasoline sold Oct-April in the UK, which is less hygroscopic for winter.)

 

Same in other world regions and different times of the year ie their winter / cold time of the year.  

 

https://en.wikipedia.org/wiki/Winter_diesel_fuel

 

 

https://www.ford.co.uk/owner/resources-and-support/ask-ford/technical-and-maintenance/maintenance/winter-diesel-problems

 

Edited 17 January, 20224 yr by roottoot

1 hour ago, craycrayfrog said:

I didn't have a clue I was on winter diesel tbh

We got that; even so its existence is an acknowledged fact, and there's a fair amount of discussion about it on this forum.

Attempted to strip the engine down today to get to the thermostat and found I was missing triple square sockets which hold on the egr connecting pipe. I've ordered the relevant o-rings and gaskets so kind of annoying I got caught out so early.

 

I dont see the need to mix triple square and torx.