Are there any common problems that can cause low mpg?

 

 Car sounds a bit tractor like but other than that runs perfectly, no smoke or excess exhaust, no misfires or errors or anything, heats up normally and maintains temperature, responsive, just getting very low mpg.

 

I do a lot of short trips and it’s more or less 100% urban, but I’m not driving it hard. 
 

 I’ll be doing an oil and filter change but the oil looks fine and filter not too bad.

That fuel consumption is so excessive that it suggests you may have a leak somewhere, if the engine was trying to burn that much fuel the exhaust would stink and be belching black fuel smoke.

It’s really weird, only other thing I can think is the computer is wrong somehow.

14 minutes ago, alff said:

It’s really weird, only other thing I can think is the computer is wrong somehow.

 

Oh dear, you can't rely on the trip computer, the only way to obtain accurate figures is to fill the tank to the brim with fuel, reset the mileage trip, drive it until you need to fill it again then calculate the consumption from the amount needed to refill the tank to the brim.

My journeys are at the other end of the scale, rural round trips of about 100 miles with a few of 10 to 20 miles; over 14,000 miles I've averaged about 46.5 mpg which tallies pretty with the display at the end of journeys.

If I blast up to the local shop and back, about 1.5 miles, I can easily get it down 18 mpg indicated, that's without any traffic or start/stops or crawling around looking for a parking spot.

 

I don't see what the oil has to do with the problem, sounds more like a fuel leak somewhere.

Did the computer previously say something quite different about the mpg, or has it always suggested this extreme consumption?

 

15 minutes ago, sepulchrave said:

 

Oh dear, you can't rely on the trip computer, the only way to obtain accurate figures is to fill the tank to the brim with fuel, reset the mileage trip, drive it until you need to fill it again then calculate the consumption from the amount needed to refill the tank to the brim.

I'm doing that now, new car, it's definitely burning through more than I would have thought, done 100 miles and below half full. But will see if the computer is accurate next fill!

2 minutes ago, Wino said:

Did the computer previously say something quite different about the mpg, or has it always suggested this extreme consumption?

 

It's a new car to me, but since I've had it, it's always said quite high consumption. (below 30)

Manual or automatic?

6 minutes ago, totoro said:

My journeys are at the other end of the scale, rural round trips of about 100 miles with a few of 10 to 20 miles; over 14,000 miles I've averaged about 46.5 mpg which tallies pretty with the display at the end of journeys.

If I blast up to the local shop and back, about 1.5 miles, I can easily get it down 18 mpg indicated, that's without any traffic or start/stops or crawling around looking for a parking spot.

 

I don't see what the oil has to do with the problem, sounds more like a fuel leak somewhere.

The oil just more for this tractor noise, thinking fresh might quiet it down. 

 

This could be the thing, because it's mainly getting used for school run (2 miles) and going to the local shops, things like that. Still feel like 15 is a bit low, but also it's the worst case use.

 

For the leaking fuel, there's nothing under the car, though I know it would evaporate quick, no smell under the bonnet, but maybe need to look into this more.

1 minute ago, Wino said:

Manual or automatic?

automatic!

Edited 16 October, 20196 yr by alff

Treat yourself to a 100 mile run around rural roads and see what it reports then.

 

An automatic will always drink more.

3 minutes ago, totoro said:

Treat yourself to a 100 mile run around rural roads and see what it reports then.

 

An automatic will always drink more.

 

It's a good idea, will give it a good run and see what it says

Needs hooking up to VCDS maybe, to see if the coolant temperature reading is plausible.   

Whereabouts are you alff?

12 minutes ago, Wino said:

Needs hooking up to VCDS maybe, to see if the coolant temperature reading is plausible.   

Whereabouts are you alff?

 

I'm in south london.

 

I've got one of these obdII bluetooth things and the torque app which work together, and give normal readings, but don't know if that compares to VCDS

Oh, OK, so you can see the coolant temperature and it's consistent with ambient (give or take) prior to a cold start?

 

I didn't think to check the sensor that way. Had a look, but car was used 2:30 hours ago, and it's reading 32, so not sure if it's reading high or if it's still holding some heat, but will check again in a little bit. 

 

Or probably tomorrow morning for better accuracy

Edited 16 October, 20196 yr by alff

Reading way lower than reality is what to watch for, as it'll result in heavy overfuelling initially.

Yours is sounding OK I think.

1 minute ago, Wino said:

Reading way lower than reality is what to watch for, as it'll result in heavy overfuelling initially.

Yours is sounding OK I think.

 

I will try giving it a better run, fill up first then after and calculate based on that. Could just be conditions it's being used in or dodgy computer. I'm pretty sure it's not leaking at least in the usual places, and the engine doesn't seem to have any bad symptoms. 

My 16v is also a heavy drinker, the thread is here somewhere. I've changed the ECT sensor, fixed an internal oil leak which needed the valve cover gasket redone, changed spark plugs for iridium NGKs, brakes were dragging, serviced the EGR and throttle body, cleaned the MAP sensor, cleaned injectors, changed the fuel pump and fuel filter, had a look up on VCDS and adapted everything.

 

I'll talk in kilometres here:

-After filling up the onboard computer says I'm good to go 600 km.

-In heavy city driving I rarely manage to best 140.

-In long trips I rarely go further than 300ish without refilling, all despite the very optimistic 6ish l/100km the odo shows.

-For the first part after filling up, the needle barely moves, I did 100km yesterday and the needle is still very close to full. Boy but once it gets moving, it moves fast!

 

-Only thing out of place is a 4 bar FPR instead of the factory 3 bar. Other that that the car is stock and in very good order, and it's always been taken care of.

 

🙃 🤷

1 hour ago, juanse_2691 said:

My 16v is also a heavy drinker, the thread is here somewhere. I've changed the ECT sensor, fixed an internal oil leak which needed the valve cover gasket redone, changed spark plugs for iridium NGKs, brakes were dragging, serviced the EGR and throttle body, cleaned the MAP sensor, cleaned injectors, changed the fuel pump and fuel filter, had a look up on VCDS and adapted everything.

 

I'll talk in kilometres here:

-After filling up the onboard computer says I'm good to go 600 km.

-In heavy city driving I rarely manage to best 140.

-In long trips I rarely go further than 300ish without refilling, all despite the very optimistic 6ish l/100km the odo shows.

-For the first part after filling up, the needle barely moves, I did 100km yesterday and the needle is still very close to full. Boy but once it gets moving, it moves fast!

 

-Only thing out of place is a 4 bar FPR instead of the factory 3 bar. Other that that the car is stock and in very good order, and it's always been taken care of.

 

🙃 🤷

 

140km a tank!! 😳Somethings definitely a miss isn't it. Hope the petrol is cheaper in Brazil!

 

I have the same fuel gauge as you, doesn't drop for ages then falls of a cliff

9 hours ago, alff said:

 

140km a tank!! 😳Somethings definitely a miss isn't it. Hope the petrol is cheaper in Brazil!

 

I have the same fuel gauge as you, doesn't drop for ages then falls of a cliff

Haha, it's Colombia we're talking about, 91RON is the best and most expensive fuel I can get a hold of! And it gets more expensive every month. Being a 98/95RON rated car it still pings like all hell and I guess the ECU is doing whatever it can to adapt to such poor fuel, must be running as rich as it can. I'm told I can get it chipped to run 91 without trouble so I'll give that a try. Many little things giving trouble lately (window regulator seized which I fixed today, lock randomly leaving me out of the car) so I've been putting the remap/chip job in the drawers while I fix everything else. 

3 hours ago, juanse_2691 said:

Haha, it's Colombia we're talking about, 91RON is the best and most expensive fuel I can get a hold of! And it gets more expensive every month. Being a 98/95RON rated car it still pings like all hell and I guess the ECU is doing whatever it can to adapt to such poor fuel, must be running as rich as it can. I'm told I can get it chipped to run 91 without trouble so I'll give that a try. Many little things giving trouble lately (window regulator seized which I fixed today, lock randomly leaving me out of the car) so I've been putting the remap/chip job in the drawers while I fix everything else. 

 

Get the remap before something blows up. Pinging/pinking is better managed these days but it's still hell on an engine. Plus your mileage should improve lots.

9 hours ago, vindaloo said:

 

Get the remap before something blows up. Pinging/pinking is better managed these days but it's still hell on an engine. Plus your mileage should improve lots.

My thoughts exactly, will give that a try as soon as I can.