7 seat SUV for motorway use - switch to petrol?

[kmpowell]

New car time and with a large young family (4 kids) I need practical & usable 7 seat space. I won't go into which car we've chosen (that's a different discussion for which we considered hugely, and are more than happy with our choice), so the only decision here is engine choice.

80% of its life will be on the motorway doing 200-400 round trips c15k miles a year, and we have another car for nipping about in and doing the school(s) run etc.

The car in question weighs circa 2.3tonnes, so it's never going to be a screamer, but I want smooth power that make the long journeys effortless.

Both engines are brand new MHEV 3.0 in-line units linked to a ZF8, producing:

Diesel
- Power: 300hp / 4000rpm.
- Torque: 650nm / 1500-2500rpm.
- 33mpg (WLTP)

Petrol
- Power: 360hp / 5500-6500rpm
- Torque 500nm / 1,750-5,000rpm
- 26mpg (WLTP)

I am naturally drawn to the diesel, mainly because I've had the non MHEV 3.0 diesel in the car it's replacing, and I know that's smooth and enough torque for motorway stints. At the same time I'm conscious of the growing war on diesels (wether I agree with it or not) and the gov't decision to outlaw fossil fuels in 2030 (but in my mind will be mainly Diesel focused). Can the MHEV tech really plug the torque gap in the petrol and see a MPG close to the WLTP figure, and can the extra 60hp make up for the 150 less torque.

I can see positives and negatives in both, and without a crystal ball I know it's a tough question to answer, but in reality the overall economics have to add up which are, residuals and MPG, all whilst satisfying the 'oomph' for my brain.

A 'Long range' Tesla MX has been totally discounted on affordability, so there's no pure electric choice. And due to the long journeys a plug-in hybrid has been discounted because I don't want to lug around all that flat battery weight with a 2.0 engine, after 70-80 miles or so.

As final food for thought, the Diesel has a 1% higher quoted RV after 4 years, and with exactly the same spec the diesel is 1% cheaper than the petrol.

After spending several hours on the internet 'researching', and at the dealer, I'm really no further forward deciding, so, if it were your money, what would you do, Petrol, Diesel?

I look forward to reading the sarcastic, angry, whimsical, but hopefully some sensible, replies this thread will bring...

[Pica-Pica]

This is a plot of F30 340i and 335d for ps per tonne (vertical axis) against rpm (horizontal axis)
The diesel produces greater ps per tonne at lower rpm, but the 340i takes over above about 4500 rpm. Driving style will determine which you prefer. I assume your comparison is on BMW Xs. I cannot comment on EVs

[Dohnut]

Personally I would go for the relaxed power delivery characteristics of a diesel in a large SUV as for me it’s all about low RPM grunt over high RPM power.

Disco by any chance?

[Sheepshanks]

Will the hybrid system be much help on motorway trips? BIL has a Lexus 450 that he does a lot of long trips in and I don't think it occured to him that on the motorway he's driving a brick with a 3.5 litre V6 petrol, so the MPG is horrible.

I like the efforltess feel of auto-diesels but I'd be nervous of buying one now. Have you looked at leasing? Could well end up more expensive but someone else would be taking the downside risk.

[kmpowell]

Pica-Pica said:

This is a plot of F30 340i and 335d for ps per tonne (vertical axis) against rpm (horizontal axis)
The diesel produces greater ps per tonne at lower rpm, but the 340i takes over above about 4500 rpm. Driving style will determine which you prefer. I assume your comparison is on BMW Xs. I cannot comment on EVs

Thanks, the low down grunt of the Diesel is the major sway for me. If only the power curves were available for the new units i'm comparing.

Dohnut said:

Disco by any chance?

Yup, in HSE S-Dynamic spec it has so much as standard that when comparing to competitors it works out cheaper (Q7 is £7k more!), and the facelift tech/engines adds alter things that were previously lacking. Very impressive package IMO that moves the Disco closer to Range levels of comfort and above the Q7/XC90 which are its only 'true' 7 seater rivals.

Sheepshanks said:

Will the hybrid system be much help on motorway trips? BIL has a Lexus 450 that he does a lot of long trips in and I don't think it occured to him that on the motorway he's driving a brick with a 3.5 litre V6 petrol, so the MPG is horrible.

MHEV isn't 'hybrid' like the Lexus is, this is Mild-Hybrid, it grabs and uses the once lost energy(from braking, deceleration etc) to fill acceleration torque gaps by using 48v tech.

Sheepshanks said:

I like the efforltess feel of auto-diesels but I'd be nervous of buying one now. Have you looked at leasing? Could well end up more expensive but someone else would be taking the downside risk.

It works out 25% more expensive leasing, but like you I am nervous, and more-so now it's actually decision time with my own money...

[Mouse Rat]

For motorway journeys diesel all the way.

On the motorway our 3.0tdi Touareg does better mpg than my 1.4l hybrid Golf GTE.

[Pica-Pica]

kmpowell said:

Pica-Pica said:

This is a plot of F30 340i and 335d for ps per tonne (vertical axis) against rpm (horizontal axis)
The diesel produces greater ps per tonne at lower rpm, but the 340i takes over above about 4500 rpm. Driving style will determine which you prefer. I assume your comparison is on BMW Xs. I cannot comment on EVs

Thanks, the low down grunt of the Diesel is the major sway for me. If only the power curves were available for the new units i'm comparing.

I am sure other petrol v diesel graphs will be similar when comparing identical engine capacities, assuming top range of both ignition modes.

[Volvolover]

Diesel for me in the OP's circumstances, nothing like a big diesel for relaxed motorway driving for those of us with relatively normal sized wallets

[ZX10R NIN]

Diesel in this case it suits the car better also the gap on fuel will be bigger on the Motorway as that's when the diesel comes into it's stride.

Also torquey engines suit SUV's.

[Summit_Detailing]

ZX10R NIN said:

Diesel in this case it suits the car better also the gap on fuel will be bigger on the Motorway as that's when the diesel comes into it's stride.

Also torquey engines suit SUV's.

Exactly this..

Cheers.

[vikingaero]

Definitely diesel.

Torque talks. I went to pick Vikingette1 up from University on Saturday in our new family bus (Passat Estate Diesel DSG). It was so comfortable and effortless. 330 mile round trip used £30 of fuel - admittedly on the way up to collect her I left early and sat in Lane 1 at 50-60mph listening to music.

In a petrol car when traffic clears it takes a lot more revs to make progress.

[henrycrun]

Evil diesel.