I recently had an MOT and service done on a Golf TSI. Since then I've noticed the MPG reading is not reaching as high as it was before. Is there anything that could have affected this? It was a full service with oil change and also two new tyres. Thinking tyres might need wearing in or a wrong type of oil was used?

The time of year, ie ambient temperature.

Ok, because the engine has to work a little harder?

Not really - it takes longer to warm up the engine, and particularly the transmission, in lower ambient temperatures so running inefficiently for longer - plus the use of the heater and lights all contribute to energy used.

Diesels are more noticeably less economical during winter because they generate less waste heat, in some cases never fully warming up all day.

E10 fuel could be the cause. The government admit that the fuel is less efficient and you could loose some 2% on your typical MPG. Colder weather does not help either

+1 re E10 - I've spotted a drop in mpg on my Skoda Superb and Fiat Panda when I had no option but to fill up with E10 as Super unleaded E5 petrol didn't seem to be available.

Now the fuel crisis has subsided and I've got Tesco Greenenergy 99 RON E5 back in my tank again normal service/mpg has been resumed. My 2014 1.4tsi Superb did 52mpg the other day on a long run.

It makes sense really as since about September Unleaded 95 has been changed from E5 to E10 across all brands. E10 has less calorific value compared to E5.

Tyres could also have a slight effect as well - which model was fitted and what fuel efficiency rating do they have?

Edited by Big John on 17/11/2021 at 09:31

Since the 1st of September we have only done about 1000 miles in the Fabia but using E10 there seems to be no difference on the (accurate) dash display. Did a 40 mile round trip the other day and the dash said 58 mpg which is the same sort of figure we have always got on that trip.

Definitely not spending an extra 10 p a litre for E5 when the car is perfectly OK on E10. Why should I add about 7% to fuel costs for no benefit.

I suppose it's hard to compare unless you compare many tanks of petrol to average the figures out. I used Spritmonitor in the past but simply can't be bothered now. The difference isn't huge anyway. Panda filled up with E5 today - I'll see how it goes.

However I tend to try and buy higher octane petrol anyway after I heard a slight pinkng windows down in France with my tsi Superb when going uphill with 95 RON( can't be heard with windows up sue to sound proofing). I filled with a higher Octane petrol and up the same hill the noise had gone. To me pinking = potential damage to the engine.

Edited by Big John on 17/11/2021 at 18:40