Vectra 150 auto

Average on the trip computer (for the 20k I’ve owned it) = 42.2mpg

When I fill up I always calc the mpg, and 40mpg is about right. This is for short-ish rural (<10 miles) journeys with little stop/start.

If I do a long motorway/A-road trip back south I can get +55mpg out of that tank.

Speed-wise, making progress and overtaking 🙂

I had the equivalent car but with the 2.2i auto engine, and averaged 32 mpg over 70k in two years – driven hard though.

So a gain of about 30% going from petrol to diesel.

And to go with PP’s motorcycle comment, 56mpg over 20k miles from a Triumph 1050 on a fast commute into London 🙂

I’ve had the car 6 years. Most people change every 3 on average I reckon, so by now I’d be coming up to my second change. That seems a fair assumption, no?

No!

You’re comparing petrol and diesel, not comparing yourself with serial car changers! If you’d bought a diesel, you’d still be keeping it just as long wouldn’t you?

You have got to love a Rover 75!! Good work old chap!

Motorway @ 70mph cruise control for an hour = 42 mpg

B roads at 30-50mph for 10 miles / 20 minutes = 44mpg

Weird.

Motorway @ 70mph cruise control for an hour = 42 mpg

B roads at 30-50mph for 10 miles / 20 minutes = 44mpg

Weird.

or 5h1t aerodynamics?

PeterPoddy – Member

This of course doesn’t take into account the higher running costs of a diesel (servicing, tyres don’t last as long etc) and the higher likelihood of something going wrong and it closing a lot more to repair.

Eh? I’m sure these ‘reasons’ are used to justify why diesels aren’t worth bothering with, but in my experience there is no real proof that they are real….

Servicing my diesel costs about the same as servicing my old 1.4 Fiesta. It does cost a little bit more, but it’s a larger engine so requires more oil, which will be a large part of the cost discrepancy. If I had bought a larger petrol engined car, I would also have expected that to cost a bit more to service.

Tyres not lasting as long on a diesel? Why is this? Presumably you are comparing tyre wear of comparable sized cars with comparable engine outputs?
I used to get about 25k miles out of a set of fronts on my Fiesta (1.4 with 75BHP) and I get around 20k miles out of my current front tyres. But, the car has 55BHP more (3x the torque) and weighs about 300kg more so extra wear is to be expected. The weight gain is largely car related, not engine related – had I gone for the petrol version of my car, it would have only been 25kg lighter).
If I had bought a diesel with comparable performance to my old petrol Fiesta I would expect tyres to last at least as long.

My diesel has been a lot more reliable than the petrol Fiesta. The only failures specifically related to the fact it is a diesel have been 2 intercooler pipes that have failed (in 253k miles), which cost £45 for one and £125 for the other.
A faulty idle air control valve on the Fiesta cost more to replace than those two ‘diesel failures’ by itself.

Kryton57
Motorway @ 70mph cruise control for an hour = 42 mpg

B roads at 30-50mph for 10 miles / 20 minutes = 44mpg

Weird.

Why is that weird? The power required to push the air out of the way goes up with the cube of speed!

So:

at low speed (<30mph), you have little or no aero drag, but huge parasitic friction from having to be in a low gear (so you engine has to turn many more times per mile driven) and the average engine power required is tiny, so the overall engine efficiency is low.

at high speed (>60mph) aerodynamic drag increases massively, but you are in a high gear, so parasitic friction is low. Overall power output is high, so overall efficiency is high

Somewhere between the two, a point exists where you only need a low amount of power to move at that speed, but the losses in making that power are also minimised. That speed is the vehicles maximal fuel economy speed, and for most passenger cars, is the slowest speed you can hold in top gear at about 1200rpm, typically 45mph these days

only failures specifically related to the fact it is a diesel have been 2 intercooler pipes that have failed

Not diesel specific. A turbo petrol car could well have an intercooler.

That speed is the vehicles maximal fuel economy speed, and for most passenger cars, is the slowest speed you can hold in top gear at about 1200rpm, typically 45mph these days

Agree, except in my auto it is 65mph before 6th gear appears

Why is that weird?

Maxtorque, thanks. I was comparing it to the manufacturers claimed 61mpg on m/ways, which as you state is probably at 56mph in 6th or whatever appropriate combo.

Octavia 4×4 2ltr 140PD 45-49mpg, usually 47. Bikes went inside.
Vivaro 115 swb 33-39mpg, usually 37. Bikes inside

It’s not a diseasel estate, but what the heck:

My Golf .. with um, a 3.2 V6.

– 25mpg overall
– 35mpg on a gentle run
– Will not crack 30 with bikes and roof box

MPG is really not the be-all and end-all. My 2008 R32 will cost me less to run than any Eurobox 1.6d I can get through our work lease car scheme, due to low depreciation. 😀

2003 Audi A4 Estate 1.9TDI 130PD. From the inboard computer for the last 56hrs of driving at an average of 35mph my mpg has been 47.7mpg. With bikes in the roof on a long run it can reduce by approx 5mpg.

Some of these figures make my car look like it’s got a drink problem!

It’s a SMax 2.2d, lots of options / glass roof so it’s heavy, and quite an old engine design I think.

It’s only used on motorways really and if I keep an eye on the instant fuel reading, I can generally get a 40 – 42mpg average at about 65 – 75mph speeds.

Mid 40s or less out of a diesel is seriously crap

Depends on the car. If it’s a white goods car like that Vectra I bought off you I’d agree. That returned circa 50mpg in my hands.

If you have something like a 3l ~300bhp modern big diesel it’s a different story. You get around 30% more to the gallon than an equivalent petrol of the same power and lower depreciation in general so the saving long term is pretty good. Cars like these aren’t about value so much, more about the way they drive at an acceptable cost. Also there are many more to choose from 2nd hand so easier to find a well cared for example. I can’t see many of few and far between high power petrol estate cars being in as good condition as the diesels. The 335D I bought was a 1 owner rich guys family holiday car!

I also run a petrol Nissan car for around town and despite being used for short trips it does 40mpg! It will likely be replaced with a petrol. I’d agree for most people if you want a ‘standard’ white goods car that these days petrol is probably the best option, or atleast as good as diesel long term with lower risk mechanicals.

15yr old Seat Alhambra 1.9TDI so a big old lump of a bus, average 45mpg over a full tank (about 600 miles), get low 50s on long cruisey journeys.

Eh? I’m sure these ‘reasons’ are used to justify why diesels aren’t worth bothering with, but in my experience there is no real proof that they are real….

Tell that to some who’s paid for a new turbo, dual mass flywheel, DPF etc….