What causes MPG to decline over time?

zeppelino

Has the performance been similar or has it tailed off over the same period?

AMc

I had a fuel injection issue with my '58 Petrol Golf.  The TFSI engine expert on the end of my mechanic's diagnostic service recommended putting Redex type cleaner through it to see if it would clear - which it did.  It also felt a bit better but that could be placebo effect and I don't log my consumption as carefully as you do!
Either way for a £5 a tank it's worth a try there aren't many cheaper ways to help an older engine   I do it on most tanks if there isn't Super available at the pump.

mjn

Try putting a can of BG44 or BG245 through, if everything else looks ok.

Also, what mileage?

imightbewrong

Not sure - don't really hammer it

imightbewrong

Just gone through 80k miles - about 10k a year

mjn

Is the engine prone to carbon build up? That will decrease MPG. A lot of Audi engines need carbon cleaning regularly.

zeppelino

Likely the same engine he has in his camper.

Unfortunately, for him, it could be the turbo...

Over by there

I got different results with different tyres and same tyres different pressures yielded different results. In the order of 5 or 6 mpg Sticking roof bars and bike carriers is akin to sticking air brakes on. Usually.

TerFar

There's a huge number of possibilities causing that problem. But from your stats, it seems to have been gradual, so it may be wear to timing chain, cam or bores.
But try all the simple checks the others have mentioned such as jacking each wheel and check for brake drag or worn bearing (try to do it at the end of a run with hot brakes). Loads of obvious things to check like filters, exhaust leak, etc.

eastsoutheast

Over time piston crowns start to pick up carbon deposits as do valves causing a reduction in burn efficiency. I doubt timing chain stretch would cause this unless it was so bad it threw up a warning light. Cataclean is well respected and reviewed so may be worth trying although i cant believe these type of products clean more than light deposits.

My comments assume injectors are clean and all filters have been replaced on schedule.

My sons 2015 SMax has just blown its engine (Piston 4 has literally melted), you would be surprised how coked up it is considering it has low mileage and FFSH.

I do believe modern emissions regulations play a part in reducing engine efficiency over time.