Do I buy a Diesel or Stick with Petrol

[alecmascot]

My C180 CGI has the 1.6L Turbo M274 engine, introduced in 2013, and it does not suffer from the timing gear issue that plagued the M271.

Then I read that DI is causing carbon build-up on the back of the valves.....for VAG as well.
If my next car is petrol it will be an M113 I think !

 

[TeddyRuxpin]

I don't really understand the 'high milage' thing. Surely it's more about how you use the car - if you do frequent short trips when the car hasn't warmed up, or if you mainly do long trips with the car when you go out in it.

If you work from home and don't use your car much, but then go on motorway drives when you do actually use the car, that's perfect. The DPF doesn't just sit there getting knackered while your car is parked.

Assuming that the petrol and diesel are costing the same, that is. If you have to pay £2k more for a diesel, then yes, if you don't do the miles then it'll take a lot of time to save the cash on the extra fuel saving of the diesel. You could just get a petrol and use more petrol, and you'll still probably be quids in 3 years later.

 

[markjay]

Then I read that DI is causing carbon build-up on the back of the valves.....for VAG as well.
If my next car is petrol it will be an M113 I think !

I have only ever used Shell V-Power in my cars, I am hoping that the detergents added to the fuel will help keep the valves clean of carbon deposits.

 

[Bellow]

Depends.

If the 5000 miles you drive a year are for example 100 x 50 mile motorway/a-road trips then diesel would still be ok.

If you’re going around town then petrol.

I don't really understand the 'high milage' thing. Surely it's more about how you use the car - if you do frequent short trips when the car hasn't warmed up, or if you mainly do long trips with the car when you go out in it.

If you work from home and don't use your car much, but then go on motorway drives when you do actually use the car, that's perfect. The DPF doesn't just sit there getting knackered while your car is parked.

Good points. And.....

Then I read that DI is causing carbon build-up on the back of the valves.....for VAG as well.
If my next car is petrol it will be an M113 I think !

..... if there is the above with a petrol - maybe diesel shouldn't be written off as readily (as I did to it).

 

[horatio]

I've got a soft spot for MB diesels but the CLK will be the last. Too many emissions related gubbins on the newer models and the threat of ULEZ extensions. A nice big V8 is actually starting to make sense.

 

[PeteTheOldGit]

Petrol all day long if low mileage, I have w205 c200 petrol and its 35mpg all day long totting around, on a run 45mpg easily achieved.

 

[Deleted member 37751]

I don't really understand the 'high milage' thing. Surely it's more about how you use the car - if you do frequent short trips when the car hasn't warmed up, or if you mainly do long trips with the car when you go out in it.

If you work from home and don't use your car much, but then go on motorway drives when you do actually use the car, that's perfect. The DPF doesn't just sit there getting knackered while your car is parked.

Assuming that the petrol and diesel are costing the same, that is. If you have to pay £2k more for a diesel, then yes, if you don't do the miles then it'll take a lot of time to save the cash on the extra fuel saving of the diesel. You could just get a petrol and use more petrol, and you'll still probably be quids in 3 years later.

This ^^

I had a similar conversation with a neighbour who only used a car to travel long distances on a weekend and advised him to buy a diesel - it’s not the total mileage you do in the year it’s the actual journeys themselves (one of his kids did Irish dancing that could see 300 in a weekend but then the car sat idle until the next weekend)

 

[PaulPJ]

Hi All, you guys have really given me lots of info and now I am not sure what to buy. I don't understand what "DI is causing carbon build-up on the back of the valves.....for VAG as well." means but I hope someone will enlighten me. In a typical month I will drive from home to Southampton twice which is mostly at 30 mph. Super market 4 to 6 times which is only 4 miles each way and once a month I will drive to Christchurch and back (70 miles) between 60 and 70 mph. All in all around 300 miles a month mostly rural with 70 miles on the A31/A338 dual carriageway. Paul

 

[Bellow]

Hi All, you guys have really given me lots of info and now I am not sure what to buy. I don't understand what "DI is causing carbon build-up on the back of the valves.....for VAG as well." means but I hope someone will enlighten me.

DI (direct injection - of fuel into the cylinder as opposed to the inlet duct upstream of the inlet valve) loses the washing effect that keeps valves clean. Without that, carbon can accumulate on the valve heads which can then affect performance due to the engine's impaired ability to 'breathe'.

In a typical month I will drive from home to Southampton twice which is mostly at 30 mph. Super market 4 to 6 times which is only 4 miles each way and once a month I will drive to Christchurch and back (70 miles) between 60 and 70 mph. All in all around 300 miles a month mostly rural with 70 miles on the A31/A338 dual carriageway. Paul

Probably enough faster running there to make diesel viable - but being neither a diesel user or fan, I'll leave it to others to comment.
I guess you could try diesel (if enough aspects appeal) and if the DPF does need more regeneration than acceptable, sell up and revert to petrol.

 

[markjay]

DI (direct injection - of fuel into the cylinder as opposed to the inlet duct upstream of the inlet valve) loses the washing effect that keeps valves clean. Without that, carbon can accumulate on the valve heads which can then affect performance due to the engine's impaired ability to 'breathe'.



Probably enough faster running there to make diesel viable - but being neither a diesel user or fan, I'll leave it to others to comment.
I guess you could try diesel (if enough aspects appeal) and if the DPF does need more regeneration than acceptable, sell up and revert to petrol.

Scary stuff!

Solving Gasoline Direct Injection Issues: The facts and fictions of GDI - Engine Builder Magazine


...but different opinion here:

Mercedes Direct Injection engines - carbon buildup

 

[SW18]

Hi All, you guys have really given me lots of info and now I am not sure what to buy. I don't understand what "DI is causing carbon build-up on the back of the valves.....for VAG as well." means but I hope someone will enlighten me. In a typical month I will drive from home to Southampton twice which is mostly at 30 mph. Super market 4 to 6 times which is only 4 miles each way and once a month I will drive to Christchurch and back (70 miles) between 60 and 70 mph. All in all around 300 miles a month mostly rural with 70 miles on the A31/A338 dual carriageway. Paul

Thanks for sharing your usage info. Reading it made me wonder: could you be radical and go electric?! On the assumption you have a driveway to charge in, your trips out could each be managed on a single charge. Admittedly, the choices of electric car are rather limited at the moment (maybe only the Leaf is a realistic option) but the running costs would be minimal. If it were me I might seriously consider a Leaf and use the savings to find an old Mazda MX-5 as an occasional fun car!

 

[Deleted member 6183]

My old 5 series was a 3.0 DI engine and I had no end of trouble with it, my mechanic would mutter about DI being crap and claimed Mitsubishi tried it and failed.

The upshot was that it ate coil packs for fun and would run very hot and lumpy, not great going around Trafalgar Square on a hot Friday afternoon which was when I made the final decision to get rid of it.

It would only run on premium fuel and hated BP of any description.

I'm hoping that it was either a duff car or that it was just BMW DI around 2007 wasn't their finest hour.

 

[unimog]

Short trips in a diesel and traffic in cities will shorten the working cycle of the particle filter/DPF. I personally wouldn't do it as the a diesel won't even get warm on those shopping runs, and even with the motorway runs you do, the extra cost of buying and servicing a diesel and for no real fuel saving I would stick with petrol. That said, diesel residuals do seem to have suffered of late...

 

[PaulPJ]

Thanks Guys, I sure did start a healthy debate by asking which would be better. I was always erring towards Petrol but the tax was lower on a diesel but I think I will go with plan A and get another petrol but make sure it has the M274 engine. I love big cars so a Leaf would be way too small for me despite the savings.

 

[jdrrco]

Good decision. I was in the same boat this time last year. Most of my trips are 2-4 miles max and I was in a 2015 CDI. Decided the options were either sensible electric/hybrid or fun petrol.

One year on in a 4.7TT V8 and I know I made the right choice.

Every driven inch is so rewarding aurally and who knows how much longer a great and a great big engine like that might even be viable. Enjoy them while you can.

Btw, off to France for the annual pilgrimage next week and delighted that the CLS500 falls into category 1 of the new French emission standards! Maybe it'll be viable for longer than I feared!!

 

[markjay]

This ^^

I had a similar conversation with a neighbour who only used a car to travel long distances on a weekend and advised him to buy a diesel - it’s not the total mileage you do in the year it’s the actual journeys themselves (one of his kids did Irish dancing that could see 300 in a weekend but then the car sat idle until the next weekend)

This is true, though the pattern you describe is uncommon... as a rule of thumb, a low-mileage car is likely to have been driven mainly short journeys, while a high-mileage car is likely to have been driven mostly on Motorways.... but there are exceptions of course.

 

[Deleted member 65149]

Regarding the possible Direct Injection issue. I’ve had my 3.5 litre DI V6 C-Class for seven years now and so far not aware of any performance impairment that could be attributed to carbon build up on the valves. There’s never been a hint of any problem, whether during periods of just very short local trips or long high-speed blats across Europe.

What may be helping is that I’ve always had the car serviced by MB where hopefully they will have always used the correct oil. Apparently DI engines are very sensitive to this.

 

[GM87]

Similar position to yourself - work from home so not doing big miles with mixed use trips as well...in the end I went 5.5l v8 petrol because you might as well enjoy the little driving you actually do as much as possible.

Cost to run vs per mile v residuals etc isn’t gonna see one head and shoulders above enough to make the call for you; for me it’s what you’ll enjoy driving the most!

 

[Alex225]

Short trips - Petrol

Long/motorway drives - Diesel

Doesn’t have to be high mileage just the type of driving that’s suited better to one or the other.

I have an E320 diesel and only do 12k a year but I do that in 250 mile stints on the M25/M4 so it’s ideal. Round town when it’s not fully warmed up it is way less efficient. Not considering DPF issues in more modern cars.

My cousin was looking at getting a new car and was looking at a diesel A Class. He hardly drives and lives in Clapham but despite my advice he bout it anyway because the salesman said, “go on the motorway occasionally and it’ll be fine”. He won’t ever do that and is the perfect candidate for potential issues. Hopefully he doesn’t experience problems but it’s simply not the right car his usage. Mileage aside.

 

[PaulPJ]

Thanks for sharing your usage info. Reading it made me wonder: could you be radical and go electric?! On the assumption you have a driveway to charge in, your trips out could each be managed on a single charge. Admittedly, the choices of electric car are rather limited at the moment (maybe only the Leaf is a realistic option) but the running costs would be minimal. If it were me I might seriously consider a Leaf and use the savings to find an old Mazda MX-5 as an occasional fun car!

I had a MX-6 as a company car back in the mid 90's. My wife loved it.