245hp vs 258hp

245hp vs 258hp

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JNW1

7,810 posts

195 months

Thursday 4th December 2014
quotequote all
Welshbeef said:
I think you'll find the very vast majority of commutes are far less than 34 miles as such its a highly representative measurement. In fact putting down a very long trip is utterly meaningless really - unless of course you do that very often.



Also to add it was 2 degrees when I set off too so a very cold start on commuting distance through have commuting traffic - possibly one of the most representative results Possible.



Clearly I could have carried on driving but guess what the mpg was increasing all the way until I came to a stop so it would actually be even higher on any longer trip -- is that the point you were making? That in fact I could have got notably higher if I'd driven 3 or 4 times the dostance which would mitigate the cold start period of low mpg plus mitigate the low mpg but of getting to the m way?
No, the point I was making was that to get an accurate representation of what average mpg a car's doing you need to measure it over a reasonably long distance in order to eliminate errors on individual tankfuls and/or journeys. So no, I wasn't suggesting you should have driven for 68 miles or even 340 miles because in isolation that's still nowhere near far enough to be truly representative; however, if you did 100 journeys of 34 miles and the average over the total mileage was still 46mpg that would be much more meaningful IMO.


gizlaroc

17,251 posts

225 months

Thursday 4th December 2014
quotequote all
ML350cdi showed 33mpg on my commute to our other place at the coast, 39 miles.

Over 15,800 miles since the last reset it is showing............25.1mpg.

It is the short 3 mile journeys from home to office that kills it, 18mpg on that run twice a day.

This is where petrol starts to make more sense, the ML500 borrowed was showing 20mpg on that short 3 mile run.




If you sit doing lots of 30mile plus trips diesel works, if you do lots of sub 30 mile or 20 minute trips it will be maybe 15% better, or in some cases as seen above actually worse.

My E39 530i got 26mpg on my old 9 mile commute in winter which was 3mpg better than the 530d it replaced.


Same with my 3.2 fsi quattro a6, 2mpg better than the 3.0tdi on that run.


However, my old 1.9tdi A4 used to see 50 average and 65 on a run no problem, but no dpf, manual 'box, 16" 205 wheels, no climate and a staggering 90bhp.

I have gone from 40k miles a year to 20k miles a year and yet I am still finding it hard to pull the trigger on a nice 6cyl petrol, I know that a diesel will cost me £700 a month and lovely petrol will cost me £800 a month and £100 in the grand scheme of things is bugger all, but it is still hard to go petrol, because I have been brainwashed.

Welshbeef

49,633 posts

199 months

Thursday 4th December 2014
quotequote all
JNW1 said:
No, the point I was making was that to get an accurate representation of what average mpg a car's doing you need to measure it over a reasonably long distance in order to eliminate errors on individual tankfuls and/or journeys. So no, I wasn't suggesting you should have driven for 68 miles or even 340 miles because in isolation that's still nowhere near far enough to be truly representative; however, if you did 100 journeys of 34 miles and the average over the total mileage was still 46mpg that would be much more meaningful IMO.
That's a fair point.




I would on a slightly different angle challenge/question why cars with the lesser powered engines and weight cannot hit over 40mpg regardless of how its driven (a bit like why do Focus ST 2.5ltr owners generally get 20ish mpg where as auto V70 estates get over 30mpg with the same engine... It is a driving style specific to certain models --- just posing that thought. ).

Fox-

13,243 posts

247 months

Friday 5th December 2014
quotequote all
Welshbeef said:
I would on a slightly different angle challenge/question why cars with the lesser powered engines and weight cannot hit over 40mpg regardless of how its driven
Because many people just get in and drive without caring, whereas you care so deeply about discussing fuel economy on the internet that even subconciously every drive is another chance to prove the internet wrong. 90% of your posts are about fuel economy. You'd have got a bigger kick out of a 520d, and I cannot for the life of me understand how you justified the money you sunk into the RS6 hehe

It is trivially easy to get way, way under 40mpg in my 530d - a car that is exactly the same age as yours, the same weight and has the same engine and the same gearbox but just one fewer turbo.

It's also very easy to top 45mpg, too, but it does require a concious effort to drive in an economical fashion.

JNW1

7,810 posts

195 months

Friday 5th December 2014
quotequote all
gizlaroc said:
ML350cdi showed 33mpg on my commute to our other place at the coast, 39 miles.

Over 15,800 miles since the last reset it is showing............25.1mpg.

It is the short 3 mile journeys from home to office that kills it, 18mpg on that run twice a day.

This is where petrol starts to make more sense, the ML500 borrowed was showing 20mpg on that short 3 mile run.




If you sit doing lots of 30mile plus trips diesel works, if you do lots of sub 30 mile or 20 minute trips it will be maybe 15% better, or in some cases as seen above actually worse.

My E39 530i got 26mpg on my old 9 mile commute in winter which was 3mpg better than the 530d it replaced.


Same with my 3.2 fsi quattro a6, 2mpg better than the 3.0tdi on that run.


However, my old 1.9tdi A4 used to see 50 average and 65 on a run no problem, but no dpf, manual 'box, 16" 205 wheels, no climate and a staggering 90bhp.

I have gone from 40k miles a year to 20k miles a year and yet I am still finding it hard to pull the trigger on a nice 6cyl petrol, I know that a diesel will cost me £700 a month and lovely petrol will cost me £800 a month and £100 in the grand scheme of things is bugger all, but it is still hard to go petrol, because I have been brainwashed.
There's little doubt in my mind that diesels make don't make much sense if you're doing lots of short journeys; the mpg is poor (as you say it can be worse than a petrol equivalent in those circumstances) and on newer ones you're likely to run into DPF problems as well. My other half has a commute which is 5 miles each way and we've just bought her an A1 with the 1.4 cylinder on demand petrol engine and S-tronic gearbox; still running-in but it seems to be doing the job quite nicely so far!

In terms of your petrol v diesel dilemma for 20k miles a year, I think it's as much about the type of car you want as anything else. I was a bit torn between 335i or 335d for my F31 but in the end I decided an F31 wasn't a sports car so I might as well have the better economy and 4WD and go for the 335d. I do think it probably loses a bit in refinement compared to the petrol but to be honest the 335d is pretty good in that respect and on balance I'm happy I made the right choice. However, if you want something that's engaging to drive IMO you need less weight, petrol and (probably) a manual box; if my circumstances were different I'd much prefer to be driving something like an M235i or a Cayman S but in fairness the F31 335d makes for a very acceptable daily driver!

converted lurker

Original Poster:

304 posts

127 months

Friday 5th December 2014
quotequote all
A friend of a friend works for Bmw power plant at hams hall as a design engineer. We had a chat recently and he said that the biggest hidden killer of mpg is cold temperature. Now I like to think I have a well developed sense of mechanic
Sympathy. I start my car, let it idle for ten second, gently move off, keep it on a light throttle and below 2200 rpm for a mile or two, speed up a bit but avoid flooring it until the water temp is in the normal range after a couple of more miles etc etc.

Apparently that's entirley the wrong approach.

Mate reckons it's fine to start, give it ten seconds at idle but after that you want to have it in sport mode gearbox and drive briskly to get heat into the engine block as quickly as possible. Avoiding the top 1000 rpm for the first five minutes would do no harm but basically the quicker you warm the the engine the quicker it is going to start delivering it's design consumption.

It's also better for the cat/dpf.

JNW1

7,810 posts

195 months

Friday 5th December 2014
quotequote all
converted lurker said:
A friend of a friend works for Bmw power plant at hams hall as a design engineer. We had a chat recently and he said that the biggest hidden killer of mpg is cold temperature. Now I like to think I have a well developed sense of mechanic
Sympathy. I start my car, let it idle for ten second, gently move off, keep it on a light throttle and below 2200 rpm for a mile or two, speed up a bit but avoid flooring it until the water temp is in the normal range after a couple of more miles etc etc.

Apparently that's entirley the wrong approach.

Mate reckons it's fine to start, give it ten seconds at idle but after that you want to have it in sport mode gearbox and drive briskly to get heat into the engine block as quickly as possible. Avoiding the top 1000 rpm for the first five minutes would do no harm but basically the quicker you warm the the engine the quicker it is going to start delivering it's design consumption.

It's also better for the cat/dpf.
I've noticed that for the first few miles from a cold start my 335d tends to avoid selecting top gear and I'd assumed that was to help it warm-up faster. There's obviously a temptation to flick the paddle to select top manually but based on the above that's probably best avoided!

theboss

6,926 posts

220 months

Friday 5th December 2014
quotequote all
gizlaroc said:
ML350cdi showed 33mpg on my commute to our other place at the coast, 39 miles.

Over 15,800 miles since the last reset it is showing............25.1mpg.
I get similar figures from my E70 40d - 33-34mpg on a sedate run is achievable but throw in the short journeys and more realistic 'M40 pace' motorway travel and its about 28mpg overall over nearly 40k miles.

It's still a damned good motor - I'm not sure how I'd fare with a 4.8i - probably 20mpg also.

I've had too many diesels over the years and its getting to the point now where I care less and less about outright fuel consumption at the expense of enjoyment. I bought a 125d on the basis I'd save a few hundred quid a month on the household fuel bill and I've just replaced fuel spend for astonishing deprecitation.

gizlaroc

17,251 posts

225 months

Friday 5th December 2014
quotequote all
theboss said:
I get similar figures from my E70 40d - 33-34mpg on a sedate run is achievable but throw in the short journeys and more realistic 'M40 pace' motorway travel and its about 28mpg overall over nearly 40k miles.

It's still a damned good motor - I'm not sure how I'd fare with a 4.8i - probably 20mpg also.

I've had too many diesels over the years and its getting to the point now where I care less and less about outright fuel consumption at the expense of enjoyment. I bought a 125d on the basis I'd save a few hundred quid a month on the household fuel bill and I've just replaced fuel spend for astonishing deprecitation.
The guy up the road from me swapped from the 535d to the 550i and he went from 34mpg combined to 29mpg combined.
The say he was chuffed is an understatement.

Mind you I keep seeing a 750i up the road and not had a chance to bump into him to ask if he has swapped again. Be interested to see what he is getting from that.

But he said he was getting 15% hit economy wise but was expecting far, far more of a difference.


Every single diesel I have owned I have been a bit disappointed with the mpg, every petrol I have owned I have been impressed with the MPG, but I still find it hard to pull the trigger on a petrol for some reason. If I bought a petrol and got what I expected to get, and know I will get, I would be chuffed, but if I bought it and got less I would be gutted and kicking myself for not going diesel.


Having said all that, I have started considering a 2 litre diesel where I know I will get 40+, even in an X3.
I took out a 20d xdrive X3 auto and saw 46mpg on my test run, the car was showing 42mpg on the obc with only 3000 miles on it, and being a demo car I think that is good.
Problem for me is the fact it is a 4cyl 2 litre diesel, but that is me just being a snob more than anything else.

But, I could save proper money each month on fuel with that, I spend around £380-450 a month at the moment, that would drop to £220-270 a month in the above.
I have found with the ML I am not fussed about having loads of power, never use it, all I want is decent comfort levels, nice sound system and job done.





Edited by gizlaroc on Friday 5th December 11:07

Wills2

22,968 posts

176 months

Friday 5th December 2014
quotequote all
converted lurker said:
A friend of a friend works for Bmw power plant at hams hall as a design engineer. We had a chat recently and he said that the biggest hidden killer of mpg is cold temperature. Now I like to think I have a well developed sense of mechanic
Sympathy. I start my car, let it idle for ten second, gently move off, keep it on a light throttle and below 2200 rpm for a mile or two, speed up a bit but avoid flooring it until the water temp is in the normal range after a couple of more miles etc etc.

Apparently that's entirley the wrong approach.

Mate reckons it's fine to start, give it ten seconds at idle but after that you want to have it in sport mode gearbox and drive briskly to get heat into the engine block as quickly as possible. Avoiding the top 1000 rpm for the first five minutes would do no harm but basically the quicker you warm the the engine the quicker it is going to start delivering it's design consumption.

It's also better for the cat/dpf.
I'd also say it's oil temp not water temp that you need to worry about before you floor it, also I've never understood people that idle their cars as there is no need.

For me the two biggest issues are cold oil and low oil pressure, idling a car gives you both. As your friend says get the engine up to temp as quickly as possible without ragging it.

Welshbeef

49,633 posts

199 months

Friday 5th December 2014
quotequote all
Wills2 said:
I'd also say it's oil temp not water temp that you need to worry about before you floor it, also I've never understood people that idle their cars as there is no need.

For me the two biggest issues are cold oil and low oil pressure, idling a car gives you both. As your friend says get the engine up to temp as quickly as possible without ragging it.
Generally to defrost and demist the screen before they set off.

gizlaroc

17,251 posts

225 months

Friday 5th December 2014
quotequote all
Welshbeef said:
Generally to defrost and demist the screen before they set off.
But that is instant these days.
Well, unless you turn the climate off sometimes I suppose.

converted lurker

Original Poster:

304 posts

127 months

Friday 5th December 2014
quotequote all
Well we only get a water temp gauge so you have to use that as a proxy for oil temp.

I was brought up as a pilot to be very gentle with engines in the first thirty seconds after start. The thermal stress, the cold oil the manifold heat shock etc. But of course that was always on low tech, high capacity gasoline piston engines.

It seems with modern diesels the thermal shock isn't so great, the tolerances are higher and you want to be using plenty of revs within a few seconds of normal starting. I tend to sit, start, seatbelt on, small throttle blip, engage gear and drive off. Then within thirty seconds put it in sport for the first couple of miles.

One other thing he was pretty adamant about was not parking the car on full lock. Potential huge problems with the electric steering gubbins lies that way,

Welshbeef

49,633 posts

199 months

Friday 5th December 2014
quotequote all
gizlaroc said:
Welshbeef said:
Generally to defrost and demist the screen before they set off.
But that is instant these days.
Well, unless you turn the climate off sometimes I suppose.
Took a couple of mins this morning with a mild frost - I can see it taking ten mins on heavily frosted up days (same as my previous cars).

Heated screen/quick clear would be very useful

pilchardthecat

7,483 posts

180 months

Friday 5th December 2014
quotequote all
theboss said:
gizlaroc said:
ML350cdi showed 33mpg on my commute to our other place at the coast, 39 miles.

Over 15,800 miles since the last reset it is showing............25.1mpg.
I get similar figures from my E70 40d - 33-34mpg on a sedate run is achievable but throw in the short journeys and more realistic 'M40 pace' motorway travel and its about 28mpg overall over nearly 40k miles.
It's almost as economical as my 997.2 C2S rofl

JNW1

7,810 posts

195 months

Friday 5th December 2014
quotequote all
gizlaroc said:
The guy up the road from me swapped from the 535d to the 550i and he went from 34mpg combined to 29mpg combined.
The say he was chuffed is an understatement.
Sounds like he needs to talk to Welshbeef to learn how to get decent economy from a 535d!

gizlaroc said:
Every single diesel I have owned I have been a bit disappointed with the mpg, every petrol I have owned I have been impressed with the MPG,
That's been my experience as well although having said that the average in my F31 335d is around 30% better than my E92 335i despite it being a bigger and heavier car. The problem is the official figures say it should be more like 50% better so at "only" 30% is the glass half-full or half-empty?!!

gizlaroc said:
Having said all that, I have started considering a 2 litre diesel where I know I will get 40+, even in an X3.
Hmm, but with the 2 litre diesel you're probably taking a significant step backwards in terms of refinement. Ok, it will be fine at 70mph in top on a motorway but sitting at traffic lights and accelerating through the gears might be a different story!

anonymous-user

55 months

Friday 5th December 2014
quotequote all
converted lurker said:
A friend of a friend works for Bmw power plant at hams hall as a design engineer. We had a chat recently and he said that the biggest hidden killer of mpg is cold temperature. Now I like to think I have a well developed sense of mechanic
Sympathy. I start my car, let it idle for ten second, gently move off, keep it on a light throttle and below 2200 rpm for a mile or two, speed up a bit but avoid flooring it until the water temp is in the normal range after a couple of more miles etc etc.

Apparently that's entirley the wrong approach.

Mate reckons it's fine to start, give it ten seconds at idle but after that you want to have it in sport mode gearbox and drive briskly to get heat into the engine block as quickly as possible. Avoiding the top 1000 rpm for the first five minutes would do no harm but basically the quicker you warm the the engine the quicker it is going to start delivering it's design consumption.

It's also better for the cat/dpf.
Little of that makes sense.

For a start, if your driving in sport mode and going close to 1000rpm of maximum, fuel consumption isn't relevant, it's going to be poor.

Secondly, any IC engine is going to experience greater levels of wear if it is driven hard with cold oil.

My 530D doesn't have a water temperature gauge, just oil and it's up at its normal running temperature in 4 or 5 miles, so I doubt it's running at what might be considered a low temperature, from the fuel consumption point of view, for long enough to be relevant.

Why don't you give your mate's method a go for a year or so and let us know how you get on? wink

Fox-

13,243 posts

247 months

Friday 5th December 2014
quotequote all
gizlaroc said:
The guy up the road from me swapped from the 535d to the 550i and he went from 34mpg combined to 29mpg combined.
The say he was chuffed is an understatement.
I think what happens is that most people buy diesel for economy and then find it quite difficult to accept that perhaps the economy isn't all that.

From cold my 530d simply isn't an economical car, it's almost as thirsty as my 530i. It's really that simple.

Get it warmed up and on a long trip and it's fairly impressive and will touch 50mpg. But unless you do mostly long trips like that there is almost no real economy benefit from a diesel and a heap of refinement disadvantages versus a petrol.

If only people actually understood this, perhaps there would have been more used 535i for me to purchase hehe

Roo3Stuart

288 posts

161 months

Friday 5th December 2014
quotequote all
gizlaroc said:
theboss said:
I get similar figures from my E70 40d - 33-34mpg on a sedate run is achievable but throw in the short journeys and more realistic 'M40 pace' motorway travel and its about 28mpg overall over nearly 40k miles.

It's still a damned good motor - I'm not sure how I'd fare with a 4.8i - probably 20mpg also.

I've had too many diesels over the years and its getting to the point now where I care less and less about outright fuel consumption at the expense of enjoyment. I bought a 125d on the basis I'd save a few hundred quid a month on the household fuel bill and I've just replaced fuel spend for astonishing deprecitation.
The guy up the road from me swapped from the 535d to the 550i and he went from 34mpg combined to 29mpg combined.
The say he was chuffed is an understatement.

Mind you I keep seeing a 750i up the road and not had a chance to bump into him to ask if he has swapped again. Be interested to see what he is getting from that.

But he said he was getting 15% hit economy wise but was expecting far, far more of a difference.


Every single diesel I have owned I have been a bit disappointed with the mpg, every petrol I have owned I have been impressed with the MPG, but I still find it hard to pull the trigger on a petrol for some reason. If I bought a petrol and got what I expected to get, and know I will get, I would be chuffed, but if I bought it and got less I would be gutted and kicking myself for not going diesel.


Having said all that, I have started considering a 2 litre diesel where I know I will get 40+, even in an X3.
I took out a 20d xdrive X3 auto and saw 46mpg on my test run, the car was showing 42mpg on the obc with only 3000 miles on it, and being a demo car I think that is good.
Problem for me is the fact it is a 4cyl 2 litre diesel, but that is me just being a snob more than anything else.

But, I could save proper money each month on fuel with that, I spend around £380-450 a month at the moment, that would drop to £220-270 a month in the above.
I have found with the ML I am not fussed about having loads of power, never use it, all I want is decent comfort levels, nice sound system and job done.





Edited by gizlaroc on Friday 5th December 11:07
To add to this discussion and in particular the longer journey point, my 535d has done 42 mpg over 45k miles from new but I only really use it for commuting so nearly all journeys are 50 miles and it does very little town work. On any decent drive it is hard to get below 40 but equally I've never been in the 50s. I think the economy is amazing for the grunt on offer and I would guess I'm saving plenty from the economy.

I would also add that my wife has an X3 with the 30d engine and it gives away 5+ mpg on a run to the 535d by pushing that big front through the air, plus a lot more road noise. But I actually think it is a really nice drive, certainly better than the 5 in some aspects.

Wills2

22,968 posts

176 months

Friday 5th December 2014
quotequote all
Welshbeef said:
Wills2 said:
I'd also say it's oil temp not water temp that you need to worry about before you floor it, also I've never understood people that idle their cars as there is no need.

For me the two biggest issues are cold oil and low oil pressure, idling a car gives you both. As your friend says get the engine up to temp as quickly as possible without ragging it.
Generally to defrost and demist the screen before they set off.
That's not what I'm talking about, some people think it's a good idea to warm the engine up at idle, I disagree.