MPG dropped for no apparent reason - why?
Discussion
Hi all,
Owned a CUPRA Leon estate for the last 6 months. It’s the 310hp one with a version of the EA888 engine, DSG, and four wheel drive.
Done about 6000 miles so far and it’s great. However…
I regularly drive from south Manchester to either York or Durham to see family. Up until the last month, the car always exceeded 40mpg.
On the last few trips, the car barely got over 35mpg.
There was nothing unusual about the journeys, traffic was normal. There are no warning lights, tyres correct pressure, same fuel as always, same driving style, same people / dog / luggage in the car.
Any ideas as to why the fuel consumption has dropped?
I can only think of lower temperatures since the summer, but I’ve done these journeys for years in several cars and never experienced this…
Owned a CUPRA Leon estate for the last 6 months. It’s the 310hp one with a version of the EA888 engine, DSG, and four wheel drive.
Done about 6000 miles so far and it’s great. However…
I regularly drive from south Manchester to either York or Durham to see family. Up until the last month, the car always exceeded 40mpg.
On the last few trips, the car barely got over 35mpg.
There was nothing unusual about the journeys, traffic was normal. There are no warning lights, tyres correct pressure, same fuel as always, same driving style, same people / dog / luggage in the car.
Any ideas as to why the fuel consumption has dropped?
I can only think of lower temperatures since the summer, but I’ve done these journeys for years in several cars and never experienced this…
Tyre pressures okay? Not changes tyres recently?
It could be all sorts of things but worth just seeing if any of the wheels are getting hot on a long run or getting excessively mucky. Both would indicate a sticking caliper. You could also jack each corner up and see if they all spin freely with no grinding noises.
It could be all sorts of things but worth just seeing if any of the wheels are getting hot on a long run or getting excessively mucky. Both would indicate a sticking caliper. You could also jack each corner up and see if they all spin freely with no grinding noises.
Its getting colder so that always increases consumption. Dont the petrol stations change the makeup of fuel between Summer and Winter, that may also have an impact although wouldn't have thought it be that big of a difference. Worth checking pressures, binding brakes and perhaps going to get an alignement too
jurph said:
Hi all,
Owned a CUPRA Leon estate for the last 6 months. It s the 310hp one with a version of the EA888 engine, DSG, and four wheel drive.
Done about 6000 miles so far and it s great. However
I regularly drive from south Manchester to either York or Durham to see family. Up until the last month, the car always exceeded 40mpg.
On the last few trips, the car barely got over 35mpg.
There was nothing unusual about the journeys, traffic was normal. There are no warning lights, tyres correct pressure, same fuel as always, same driving style, same people / dog / luggage in the car.
Any ideas as to why the fuel consumption has dropped?
I can only think of lower temperatures since the summer, but I ve done these journeys for years in several cars and never experienced this
Weather is colder and wetter so the air is denser and the road has higher rolling resistance so that may account for the drop. Running lights and heating also have an impact. Seems quite a significant drop though if no other factors have changed. Owned a CUPRA Leon estate for the last 6 months. It s the 310hp one with a version of the EA888 engine, DSG, and four wheel drive.
Done about 6000 miles so far and it s great. However
I regularly drive from south Manchester to either York or Durham to see family. Up until the last month, the car always exceeded 40mpg.
On the last few trips, the car barely got over 35mpg.
There was nothing unusual about the journeys, traffic was normal. There are no warning lights, tyres correct pressure, same fuel as always, same driving style, same people / dog / luggage in the car.
Any ideas as to why the fuel consumption has dropped?
I can only think of lower temperatures since the summer, but I ve done these journeys for years in several cars and never experienced this
Something else to consider is that the ethanol content of petrol becomes less efficient in colder temps so an ECU will adjust for more fuel to compensate.
We don't switch to a winter blend for petrol in the U.K. which in some countries causes a drop in calorific value so more fuel is burned to compensate.
Would all this add up to a >10% drop on a car? Doesn't seem too likely but a high performance engine with a 4WD drivetrain would show a bigger drop than Ethel's Jazz.
Is it actual measure MPG or what the trip computer says? The VAG trip computers can be quite inaccurate sometimes.
Wet roads, particularly on something with wide tyres can make quite a difference to MPG. Its also possible the tyres are now worn to a point where there are less efficient at pushing water away - not necessarily to a level affecting safety or handling but enough to impact on rolling resistance.
Wet roads, particularly on something with wide tyres can make quite a difference to MPG. Its also possible the tyres are now worn to a point where there are less efficient at pushing water away - not necessarily to a level affecting safety or handling but enough to impact on rolling resistance.
Fuel supplier taking more advantage of 'up to' 10% ethanol?
If you had a £10 ODB reader and torque app on your phone you can look at the fuel trims.
Ive tested it on my wifes car a few times, it always gets more MPG on 'super' vs E10, and, after a time (or a reset ) you can see it in the long term fuel trim.
('By more, i'm talking 25 vs 22 mpg, which at that scale, pays for the premium over E10. 3mpg on a little supermini wouldn't be worth talking about.
My car I only ever put E5 in as i dont want my K-jet system gummed up)
If you had a £10 ODB reader and torque app on your phone you can look at the fuel trims.
Ive tested it on my wifes car a few times, it always gets more MPG on 'super' vs E10, and, after a time (or a reset ) you can see it in the long term fuel trim.
('By more, i'm talking 25 vs 22 mpg, which at that scale, pays for the premium over E10. 3mpg on a little supermini wouldn't be worth talking about.
My car I only ever put E5 in as i dont want my K-jet system gummed up)
Thanks for the input so far.
Looks like a sticky caliper or weather could be the most likely candidates. Although never noticed weather doing this on other high performance cars I’ve had.
I fill up with regular Shell unleaded, can’t imagine this changes too much but could definitely be wrong.
I am using the OBC to measure MPG. I know this may not be the most accurate, but surely it will be consistently inaccurate (if that makes sense), so a 5mpg drop is still a 5mpg drop.
Looks like a sticky caliper or weather could be the most likely candidates. Although never noticed weather doing this on other high performance cars I’ve had.
I fill up with regular Shell unleaded, can’t imagine this changes too much but could definitely be wrong.
I am using the OBC to measure MPG. I know this may not be the most accurate, but surely it will be consistently inaccurate (if that makes sense), so a 5mpg drop is still a 5mpg drop.
If we assume that the car is driven exactly the same, discount weather and fuel mixture, there are a few reasons why a car will start to run less efficient.
Could be something as simple as:
Worn spark plugs
Throttle body sticking
Dirty fuel filter
O2 sensor not reading correctly
Clogged air filter
Hole in exhaust
Could be something as simple as:
Worn spark plugs
Throttle body sticking
Dirty fuel filter
O2 sensor not reading correctly
Clogged air filter
Hole in exhaust
jurph said:
Thanks for the input so far.
Looks like a sticky caliper or weather could be the most likely candidates. Although never noticed weather doing this on other high performance cars I ve had.
I fill up with regular Shell unleaded, can t imagine this changes too much but could definitely be wrong.
I am using the OBC to measure MPG. I know this may not be the most accurate, but surely it will be consistently inaccurate (if that makes sense), so a 5mpg drop is still a 5mpg drop.
I have a Golf R with the same engine. Looks like a sticky caliper or weather could be the most likely candidates. Although never noticed weather doing this on other high performance cars I ve had.
I fill up with regular Shell unleaded, can t imagine this changes too much but could definitely be wrong.
I am using the OBC to measure MPG. I know this may not be the most accurate, but surely it will be consistently inaccurate (if that makes sense), so a 5mpg drop is still a 5mpg drop.
Economy can vary wildly, they can do the whole 40mpg thing, but it doesn't take much for it to drop. Use any of the performance, colder weather etc.
If I were you, I'd switch to Super Unleaded. It costs a little more, but you'll make it back in improved economy. Tesco Momentum is really good because it's easy to find, and they sell a decent amount of it so it doesn't sit around under petrol stations for weeks, obvs whatever is most practical for you, but try to get something 98 or above (mine shows 98 E5 or E10 inside the fuel flap as recommended, but 95 works). Try it for a tank or two and see how it goes.
Similar but different...
...for a dozen years or so I drove my Golf R32 and then Golf R from Nottingham to London & back three weekends a month.
If it rained hard I noticed the MPG used to drop significantly. I always wondered if this was the 4WD system engaged itself in the heavy rain.
...for a dozen years or so I drove my Golf R32 and then Golf R from Nottingham to London & back three weekends a month.
If it rained hard I noticed the MPG used to drop significantly. I always wondered if this was the 4WD system engaged itself in the heavy rain.
My CLS 350d MPG drops around 3-5 mpg in the winter.
Cooler air is more dense so wind resistance is higher.
Tyre rolling resistance increases in cooler temps.
All marginal stuff but it adds up.
The weirdest one was when I filled a few times with ‘super’ diesel. Not only did the actual fuel consumption increase, but the car started to understate its fuel consumption where generally it says it uses a bit more than it actually does.
Cooler air is more dense so wind resistance is higher.
Tyre rolling resistance increases in cooler temps.
All marginal stuff but it adds up.
The weirdest one was when I filled a few times with ‘super’ diesel. Not only did the actual fuel consumption increase, but the car started to understate its fuel consumption where generally it says it uses a bit more than it actually does.
We had a little Mitshubishi Colt in the family (youngest daughters car) that she filled up weekly. Then it suddently needed to be a day earlier each week. I couldn't find anything wrong, and neither could the dealer or our village garage. We didn't have an accurate check of its prior fuel consumption, but the new fuel consumption was 40MPG, vs somewhere in the region of 50MPG before. Never got to the bottom of it.
I spreadsheeted the fuel consumption on my car anyway as I used it for work, and I started doing wife's too so I'd have something to refer to if it ever happened again.
I spreadsheeted the fuel consumption on my car anyway as I used it for work, and I started doing wife's too so I'd have something to refer to if it ever happened again.
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