Diesel................Or Petrol?

[xtrailman]

When i had the Audi 1.8 turbo, 180bhp, on a run the best i would get was 33mpg, the car weighed around 1550kg.

Yesterday i did a 5 hour in total round trip, with a 2litre 170bhp turbo diesel, the computer ended on over 48mpg, pulling 1720kg.

That's why i use a rattly diesel.

 

[Gafferbill]

In 1974 I fitted a 1.5 ltr British Leyland diesel engine to a Wolsely 16/60.
The car returned 45mpg as opposed to the 28mpg of the standard petrol version.

In 1989 I purchased a Rover Montego 2ltr diesel estate.
The car was fitted with a Perkins Prima engine and could deliver 100mpg or 100 mph depending on how it was driven.
I could get 50+mpg solo and 38mpg towing an 1150kgs caravan.

I currently have a 1.4ltr Ford diesel that never drop below 53mpg with over 60mpg on the motorway and a 2.7ltr diesel 4x4 that does 30mpg solo and 22mpg towing.

…… guess what my answer to the OP’s question is.

 

[otherclive]

Yes the diesel is more economical than a petrol but you have to look at total costs of ownership not just mpg. Diesel cars are likely to be more expensive than petrol to purchase, their servicing costs tend to be higher on a like for like basis and the CRD fuelling system components are significantly more expensive than for a petrol car. So whilst mpg is one factor you have to look at total ownership costs which must include your driving style and needs too. if you are working with a company car, list price and emissions have to be factored into the tax calcs. For solo use fleet managers still recommend petrol for mileages up to 20000 miles. But few caravanners use head over heart, me included. If cost were an issue I'd have sold the van years ago!

 

[emmerson]

I'm intrigued by these "average" mpg figures. My neighbours old Honda Jazz once showed 67 mpg on its computer thing, so he used to say it did 67 mpg. Yes it did. Once.
I had a Ford Scorpio which had a fuel computer. On a long downhill straight with foot off the loud pedal this computer showed 99.9 mpg. Going up the other side it with foot on floor it showed 0.6 mpg. Does this mean that the car averaged 50.25 mpg?

 

[Gafferbill]

I can only speak for myself…………..

The Montego did 150,000 miles in my ownership from new and apart from service items only suffered one failure with a head gasket.
My Nissan Terrano has done 100,000 miles from new and has only suffered one failure with an Air mass sensor.
I do not have excessive service costs as I do my own maintenance.

I do think that the current crop off diesels are over complicated and I would be very wary of buying a diesel without at least 5 years proven design and reliability.

The mpg figures I quoted are miles driven for fuel put in the tank except the motorway figure for the 1.4ltr Ford.

 

[otherclive]

Gafferbill,
I agree totally and you have also had the experience of long and relaible service from 'older-design' diesels. As I said above pre EU3 diesels were exceptional for reliabilty, simplicity and longevity. EU5 ones are proving problematic and shudder to think what the forthcoming EU 6 ones will do! The first owner can often live with any issues as they will be covered under warranty but the second and subsequent owners may well find then expensive to keep on the road.

 

[xtrailman]

I'm intrigued by these "average" mpg figures. My neighbours old Honda Jazz once showed 67 mpg on its computer thing, so he used to say it did 67 mpg. Yes it did. Once.
I had a Ford Scorpio which had a fuel computer. On a long downhill straight with foot off the loud pedal this computer showed 99.9 mpg. Going up the other side it with foot on floor it showed 0.6 mpg. Does this mean that the car averaged 50.25 mpg?

No that's the instantaneous reading, much like the old vacuum gauge, i had one on my mk1 cortina.
You need to look at the average reading, and there not far of on a modern car.
I have never had more than 49 mpg out of the xtrail, usually its reading 39mpg around town, but that's not in town mpg, as the most i normally do is drive through Rotherham town centre.

 

[seth1]

Conserning reliability the newer diesels are never going to be as reliable as older diesels let alone a perkins prima which were excellant in everyway.But they have got more reliable in other ways for instance when was the last time you seen a head gasket getting changed on a 2.0 vw diesel.In years gone by most diesels suffered with this failure,or diesels with excessive black smoke?
On the scale of things i dont think their as bad as people make out.Take VAG group 80% of their output must be diesel powered and infact they are now dropping the tdi badge as the mainstay are diesel.I could never go back to driving a naturally aspirated petrol,so boring.

 

[otherclive]

While NA petrols might be 'boring' I have towed with 2.3litre turbo Saab and Volvo V70turbo and both more than ably coped with the caravan weighing 1400 kg and solo they were good driving cars.

 

[cooky1]

NA aspirated petrols boring - my 4.6 V8 isn't

 

[seth1]

I expect it isnt boring,but then again neither is the fuel consumption.But make a fare comparison.A X5 4.0D isnt boring either,and it has the best of both worlds,performance and fuel ecomomy.

 

[colin-yorkshire1]

NA aspirated petrols boring - my 4.6 V8 isn't

Errrmm try a 78 trans-am with twin 4 barrel hollies, boring no way but it cost a fortune to run decades ago when 5 star petrol was £1 a gallon
while it is true that modern diesels are a bit over complicated and the newer breed of petrols are catching up fast with economy and flat power curves , personally I would never go back to a petrol,

 

[emmerson]

I expect it isnt boring,but then again neither is the fuel consumption.But make a fare comparison.A X5 4.0D isnt boring either,and it has the best of both worlds,performance and fuel ecomomy.

But it's a BMW!. My 4.2 Range Rover on LPG sure isn't boring, and it's reasonably economical

 

[seth1]

Right ok your 4.2 may not be boring but now we might as well compare electric cars for what its worth.I understood we were discusing reference petrol from a garage forecourt not LPG.How long before LPG rises in price?Are we saying for a normally aspirated petrol to have some go about it,it has to be over 4litres?Please compare like for like.

 

[emmerson]

Seth, I've been running LPG for about 15 - 20 years, and ever since I bought my first LPG car, people have been saying " ah but wait till it goes up". I'm still waiting! As for the OP not including LPG, the question was to compare petrol and diesel. I simply suggested that there is a third alternative.

 

[seth1]

No thats fair comment.Lpg is something ive never considered really.The reason being were we live the availability of the stuff,i dont recall ever seeing it in the garages i use.I once got involved with the conversion of a set of Scania industrial diesel engines to LPG,that was a very interesting job.It was also a success.When a person thinks how crude the conversion was,you would think it wouldnt work but it did.

 

[JonnyG]

Diesel driven vehicles compaired like for like with petrol driven vehicles, will always be over 20% plus, better on fuel consumption, that isnt going to change. What i find amazing is how chineses whispers works. DMF! 10s of millions fitted to both diesel and petrol cars! they do go wrong at times, in both types of vehicles, but from what you read on forums one would imagine it was a foregone conclussion to effect everyone! same applies to DPF maf and every new latest ad ons... Amazingly they dont, it is extremely rare,[ and rare means as a percentage so even a 1000 going wrong is nothing when compaired to a million units] 1% Wow...... interestingly that is lower than the chance of an LPG kit failure.or a cambelt snapping on a petrol engines............

 

[xtrailman]

Diesel engines can have cam belts too.
I recall a moderator on HJ site that had the v6 audi 2.5 diesel, years ago, the belt snapped which resulted in a new engine.

 

[RogerL]

Diesel engines can have cam belts too.
I recall a moderator on HJ site that had the v6 audi 2.5 diesel, years ago, the belt snapped which resulted in a new engine.

Fiat and Vauxhall diesels have belts.

 

[Sedo]

Concerning modern diesels we run a 54 plate Fiat Panda 1.3 turbo diesel for 'knocking around' and a 56 plate Sedona TS for towing.
As with other people have with their towcars, the Sedona only goes out seriously for towing or when we need the room.
The Fiat has 91k on the clock and still goes like a train, unfortunately the only problem we've had is the EGR valve, which has now been on for a while. According to the paperwork we inherited when we bought it, it had, had a new EGR fitted 10 months before.
If and when we change it'll be a petrol.
The Sedona's great for towing and overall we're very pleased with the Panda but petrol is our future choice for a town run around.

 

[xtrailman]

The last petrol i had came with a HT coil/pack for each spark plug.
At the time VAG was having a massive failure rate with coils going, that was back in 2000.
So don't forget with a petrol, you have those that can potentially fail, and the plugs to replace when due.
A lot of faults i had with petrol were often spark ignition problems.
In fact the last time i had a breakdown was due to damp on the HT coil.

 

[seth1]

Seriously i think the only petrol out there at the moment to tackle a diesel for fuel economy is fiats twin air 800cc supercharged unit.Even qualifies for 0 VED.Its only draw back is the retail price.About £2500 more than the closest 1.2 petrol,that to me is quite a few years worth of VED,i think it worked out at 66 years at the price we pay for the 1.2 engined petrol.
As regards to EGR failures its mainly down to low quality fuels.Speaking for the Fiat/Alfa/Lancia/Vauxhall Diesels the actual EGR valve is able to be cleaned out and rarely ever needs replacing.There is also a mod that no one bothers with which involves fitting a blanking plate in place of the tin metal gasket.The blanking plate has a 6mm hole instead of a 40mm hole.

 

[otherclive]

DMF flywheel/clutches only tend to go if the clutch is 'ridden' or let out slowly as a noorm when driving. If you push the clutch in when halted annd put in neutral and the put in gear and let it out smoothly then the DMF will (should) last as long as the non DMF clutch asssembly. But along with DPFs the car development engineers don't drive like lots of Joe Publics that is when faults start to appear.

 

[JTQ]

As regards to EGR failures its mainly down to low quality fuels.Speaking for the Fiat/Alfa/Lancia/Vauxhall Diesels the actual EGR valve is able to be cleaned out and rarely ever needs replacing.There is also a mod that no one bothers with which involves fitting a blanking plate in place of the tin metal gasket.The blanking plate has a 6mm hole instead of a 40mm hole.

Well first we run all our UK mileage on Shell and still had both fail at 27k so I personally doubt the fuel association.
I am also inform that as from this year it will be an immediate MOT failure for blanked EGRs certainly I was told that for my Euro 4 equipped engine where their operation is 'seen' by the engine management system.

 

[seth1]

Who mentioned blanking EGR valves off?My post refers to a factory mod which basically is a reduction in size of the hole in the gasket for a particular make of vehicle.I would not advise anybody to "blank" off an EGR mechanism with out seeing problems arise.Instead repair the problem.As a matter of course for the amount of time the EGR actually opens and also when it opens it wouldnt make a great deal of difference disabling the feature.