Diesel Fuel Consumption - Short Trips

[Red diesel]

okay - an old indirect injection diesel - was doing 42 to 44 miles to the gallon when used as main family car doing 15 000 miles a year.

However new car purchased just over 2 years ago - old car kept as a runabout/spare car, new car gets used for the main bulk of driving. The old

car is now used for short drives (mummy red diesel refuses to drive the new car) mainly - between 1 to 5 miles. Meaning that youd expect fuel consumption to be higher. But the damn thing now seems to be only doing 34 miles to the gallon, a drop of over 10 miles to the gallon. If it was a petrol - id say this was perfectly normal and due to the fact that it isn't warmed up and is thus always in automatic choke (older carb equipped cars) or in cold mode (for want of a better description - on newer fuel injected petrols with electronics).

I always thought that (on older diesels at least) that short journeys didn't make much difference on diesels - but am i right, we had a Nissan Sunny diesel years ago and the reason we went diesel with that particular fine (lol) piece of engineering was because although there was only 5 or 6 mpg between diesel and petrol in fuel terms. There would be a much bigger difference we were told at the time during short trips of which we were making quite a few.

If i am right in thinking that the car is using too much fuel (even taking into account the fact its only used for short journeys these days) what would be causing it. It seems to drive fine (albeit using some oil between services) and starts perfectly first turn of the key. It doesn't use water although it does smoke a bit when started first thing in the morning for about 3 or 4 minutes. Passed its NCT without issue back in June - at this level of fuel consumption. Injectors haven't been touched since we bought the car 100k miles ago.

Thanks in advance for any help recieved

Red diesel

[Cyker]

I don't know where this idea that diesels aren't affected by short journeys came from but it's totally bogus.

Unlike petrols, diesels work best when they're running hot and really need to be at optimal operating temperature to be efficient, but they take a lot longer to warm up than petrols.

In winter, I can get half way to work before the cold temp light goes out unless I'm really gunning the engine (Which, ironically, is what you're NOT supposed to do when the engine is still cold!)

When diesels are cold, the cylinder block saps a lot of the heat from the combustion which wastes a lot of power and fuel. As the cylinder block warms up, the engine gets more efficient until it reaches optimal temps, but for short journeys it'll never get to that point and it'll be burning more fuel than it would otherwise need to.

Diesels will beat pretty much anything on long distance journeys, but they really do lose out on short journeys.

[Red diesel]

I don't know where this idea that diesels aren't affected by short journeys came from but it's totally bogus.

Unlike petrols, diesels work best when they're running hot and really need to be at optimal operating temperature to be efficient, but they take a lot longer to warm up than petrols.

In winter, I can get half way to work before the cold temp light goes out unless I'm really gunning the engine (Which, ironically, is what you're NOT supposed to do when the engine is still cold!)

When diesels are cold, the cylinder block saps a lot of the heat from the combustion which wastes a lot of power and fuel. As the cylinder block warms up, the engine gets more efficient until it reaches optimal temps, but for short journeys it'll never get to that point and it'll be burning more fuel than it would otherwise need to.

Diesels will beat pretty much anything on long distance journeys, but they really do lose out on short journeys.

Thanks for that - interesting stuff, i knew that the short runs would affect fuel consumption but not to the extent it has, interestingly it got a longer drive out this week and its looking like clocking up an extra 80 to 100 miles on the tank its on now.

Red diesel

[Cyker]

Yeah, it's pretty shocking how much more fuel they use when cold!

My dad only drives his TDCI Focus to work when it rains and normally gets about 300-miles out of the tank. I've been borrowing it a fair bit lately (My Yaris, while awesome, is literally a pain in the backside for long distance journeys! ); With 4 trips to and from Birmingham plus an airport journey, I've literally doubled the mileage gotten out of the tank!

That sort of short journey stuff is where electric hybrids are the strongest tho'; My dad could complete his to and from work journey without the ICE ever having to start up potentially!

Alas they're still way too expensive to be a viable purchase for him:(

[Karma Supra]

I notice that on my daily commute the M3 gets slightly better MPG than the surf.... but if I am behaving ona long motorway haul I can get more mpg from the surf....

That said I drove all the way from Bonn Germany to home (Henley) to the pub and back and to work the next morning on tankfull in the M3. The Aygo I was convoying with had to stop for fuel on the way back and we both started with full tanks!

[Red diesel]

Yeah, it's pretty shocking how much more fuel they use when cold!

My dad only drives his TDCI Focus to work when it rains and normally gets about 300-miles out of the tank. I've been borrowing it a fair bit lately (My Yaris, while awesome, is literally a pain in the backside for long distance journeys! ); With 4 trips to and from Birmingham plus an airport journey, I've literally doubled the mileage gotten out of the tank!

That sort of short journey stuff is where electric hybrids are the strongest tho'; My dad could complete his to and from work journey without the ICE ever having to start up potentially!

Alas they're still way too expensive to be a viable purchase for him:(

What size tank is in the Focus - fairly heavy on fuel by the sounds of things - folk seem to get 50 or 60 mpg normally out of these especially the 1.6 TDCIs. I suspect this all means that for predominately short drives (we live in a rural area so public transport is a non runner ) petrol is the better option. Going petrol also opens up far more replacement options as makes you wouldn't touch with a 50 foot pole in diesel form (Mazda for example) are actually very good as petrols in terms of things like reliability.

A high mileage petrol car in excellent condition would seem to be an ideal candidate - cheap on account of high miles but if bought right - with all the short journeys you will pull the mileage back in line with the norms within a few years.

Red diesel

[gordonD4D]

Yeah, it's pretty shocking how much more fuel they use when cold!

My dad only drives his TDCI Focus to work when it rains and normally gets about 300-miles out of the tank. I've been borrowing it a fair bit lately (My Yaris, while awesome, is literally a pain in the backside for long distance journeys! ); With 4 trips to and from Birmingham plus an airport journey, I've literally doubled the mileage gotten out of the tank!

That sort of short journey stuff is where electric hybrids are the strongest tho'; My dad could complete his to and from work journey without the ICE ever having to start up potentially!

Alas they're still way too expensive to be a viable purchase for him:(

What size tank is in the Focus - fairly heavy on fuel by the sounds of things - folk seem to get 50 or 60 mpg normally out of these especially the 1.6 TDCIs. I suspect this all means that for predominately short drives (we live in a rural area so public transport is a non runner ) petrol is the better option. Going petrol also opens up far more replacement options as makes you wouldn't touch with a 50 foot pole in diesel form (Mazda for example) are actually very good as petrols in terms of things like reliability.

A high mileage petrol car in excellent condition would seem to be an ideal candidate - cheap on account of high miles but if bought right - with all the short journeys you will pull the mileage back in line with the norms within a few years.

Red diesel

the mrs has a mazda 3 , we bought the 1.4 version which is as rare as hens teeth thinking it would be more economical than the 1.6 but with the size of the car the 1.6 is the far better option to be honest, the 1.4 is still a good little car but the engine has to be worked that little bit harder pulling away and on inclines

[Cyker]

Yeah, it's pretty shocking how much more fuel they use when cold!

My dad only drives his TDCI Focus to work when it rains and normally gets about 300-miles out of the tank. I've been borrowing it a fair bit lately (My Yaris, while awesome, is literally a pain in the backside for long distance journeys! ); With 4 trips to and from Birmingham plus an airport journey, I've literally doubled the mileage gotten out of the tank!

That sort of short journey stuff is where electric hybrids are the strongest tho'; My dad could complete his to and from work journey without the ICE ever having to start up potentially!

Alas they're still way too expensive to be a viable purchase for him:(

What size tank is in the Focus - fairly heavy on fuel by the sounds of things - folk seem to get 50 or 60 mpg normally out of these especially the 1.6 TDCIs. I suspect this all means that for predominately short drives (we live in a rural area so public transport is a non runner ) petrol is the better option. Going petrol also opens up far more replacement options as makes you wouldn't touch with a 50 foot pole in diesel form (Mazda for example) are actually very good as petrols in terms of things like reliability.

A high mileage petrol car in excellent condition would seem to be an ideal candidate - cheap on account of high miles but if bought right - with all the short journeys you will pull the mileage back in line with the norms within a few years.

Red diesel

I forget off the top of my head, but I think it's a 1.7 TDCI.

It's great on the motorway, very frugal, but gets punished pretty badly for short town trips.

The car's pretty much set up for motorway cruising; The gearing is much longer than my Yaris or my brother's Corolla 2.0D4D so it runs 500-800rpm lower at a given speed but that actually hurts the mpg in town.