Diesel or petrol?

[Alex240]

Ok, I was sure this must have been discussed at some point and so I searched for a thread on it. If there is one already, I couldn't find it. If there is one that I missed could someone please direct me to it so this thread can be ignored or deleted.

I'm simply interested in the views people have on diesel & petrol engines. I'm not a mechanically minded person but I am interested in the reasoning behind people's choice to buy a vehicle with either a diesel or a petrol engine.

-Why do we even have these two different forms of fuel?
-What's the difference between the two?
-How do each of them affect vehicle performance & longevity?
-Why would you choose one over the other?

These are just a few questions on the subject that I'd really be interested in seeing discussed.

 

[L John]

-Why do we even have these two different forms of fuel?
When crude oil is separated into its component parts, two of those parts are diesel and petrol, you cant make petrol by thinning the thicker diesel part.

-What's the difference between the two?
Diesel has more energy per gallon but burns slower.

-How do each of them affect vehicle performance & longevity?
Diesel is an oil so it lubricates as it's used but petrol engines last well without the need to re-bore these days. Diesels may still have the edge though.

-Why would you choose one over the other?
Diesel was very popular due to the extra energy per gallon and lower price than petrol. These days diesel is around the same price so the benefit is just on MPG, lower RPM and grunt. Diesel burns slow for great torque (pulling power). Petrol burns faster leading to higher RPM engines and can develop more HP but again diesels these days are well up there in the HP for the same CC engines, the diesel engine is still a heavier engine though so not as nimble.

Some info in the quote.

 

[Alex240]

Some info in the quote.

Thanks, that's great information. That leaves me a bit more open to the possibility of choosing a diesel.

 

[L John]

Also a petrol engine needs electrics to run, a diesel can run without any electric if it has a mechanical fuel pump and a mechanical movement to give the engine an initial spin.

Diesel is a simpler design but costs more to service.
Diesel ignites by heat caused by compression alone (glow plugs help when the engine is cold)
Petrol needs a spark at exactly the right time.

There's a lot more to it, e.g. petrol engines generally run cleaner and sound nicer.

People say diesels don't rattle these days but even the best do at tickover due to very high compression.

You will find some people prefer petrol engines, some prefer diesel, some used diesel for better MPG but would otherwise buy a car with a petrol engine.

Diesels are getting a bad name these days due to VW and other manufacturers are worried about their emissions.

VED has been based on CO2 emmisions for decades but that may change in the not too distant future.

America has very few diesels, around 5% if memory serves.
There are good reasons for that and we may follow.

 

[Alex240]

Also a petrol engine needs electrics to run, a diesel can run without any electric if it has a mechanical fuel pump and a mechanical movement to give the engine an initial spin.

Diesel is a simpler design but costs more to service.
Diesel ignites by heat caused by compression alone (glow plugs help when the engine is cold)
Petrol needs a spark at exactly the right time.

There's a lot more to it, e.g. petrol engines generally run cleaner and sound nicer.

People say diesels don't rattle these days but even the best do at tickover due to very high compression.

You will find some people prefer petrol engines, some prefer diesel, some used diesel for better MPG but would otherwise buy a car with a petrol engine.

Diesels are getting a bad name these days due to VW and other manufacturers are worried about their emissions.

VED has been based on CO2 emmisions for decades but that may change in the not too distant future.

America has very few diesels, around 5% if memory serves.
There are good reasons for that and we may follow.

Even more great information, thank you. I've never had a diesel, & I've always totally discounted having one as even a possibility when choosing a car. I think the rattling -'I'm about to drop out onto the road'- sound the old ford work vans used to make, put me off diesels forever.
Thanks for all the information. I think I'll still stick to petrol. I'm not concerned wth MPG & I want as quiet and smooth a drive as possible.

 

[Taffy7hfa]

Reasons I love Diesel engines…….
They have superb torque curves, which leads to effortless power delivery, they can cruise at motorway speeds at less the 2000 rpm. They laugh at hills and towing, they use less fuel, they sound awesome, they are more reliable and they are capable of intergalactic mileages.
Have a look on auto trader and see how many petrol engine cars you can find that are worth anything at all once above 200k. By contrast there are several hundred diesel engine vehicles with in excess of 300k miles that are still fetching strong money.:smile:
http://www.autotrader.co.uk/classified/advert/201609308304705?make=mercedes-benz%26model=cla-class%26utm_source=Email_a_Friend%26utm_medium=Email%26utm_campaign=Email_a_friend_car

 

[Yugguy]

Thread number 987585486 on petrol vs diesel.

 

[Alex240]

Thread number 987585486 on petrol vs diesel.

Sorry to bore you, but a search for "diesel or petrol" didn't bring up the other 987585485 for me to read. I'm glad I started this thread, it's given me & perhaps others who might look, some great information.

 

[Taffy7hfa]

https://youtu.be/UiiqiiTDj0A

 

[Alex240]

Reasons I love Diesel engines…….
They have superb torque curves, which leads to effortless power delivery, they can cruise at motorway speeds at less the 2000 rpm. They laugh at hills and towing, they use less fuel, they sound awesome, they are more reliable and they are capable of intergalactic mileages.
Have a look on auto trader and see how many petrol engine cars you can find that are worth anything at all once above 200k. By contrast there are several hundred diesel engine vehicles with in excess of 300k miles that are still fetching strong money.:smile:
http://www.autotrader.co.uk/classified/advert/201609308304705?make=mercedes-benz%26model=cla-class%26utm_source=Email_a_Friend%26utm_medium=Email%26utm_campaign=Email_a_friend_car

Thanks for the input. It's great to read people's thoughts on the matter. I've always wanted to understand the differences, & pros & cons of diesel & petrol engines, & I've gained a much better understanding of it from the responses so far.

 

[L John]

Sorry to bore you, but a search for "diesel or petrol" didn't bring up the other 987585485 for me to read. I'm glad I started this thread, it's given me & perhaps others who might look, some great information.

It's a forum not a library.
If there's a useful previous thread I'm sure someone will put a link up to it.

In the meantime, chat away.....

 

[Alex240]

https://youtu.be/UiiqiiTDj0A

Thanks. That's some seriously old-school presentation. It's actually quite fun listening to that narrator talk, they don't make them like that anymore.

 

[shine]

I have to say glad MB don't put the diesel engine in the CL and SL range...But why don't they?

 

[malcolm E53 AMG]

The big issue for me when buying my 212 estate last year was that the choice of secondhand car was heavily restricted when looking at petrol engines only in the 3.5 litre capacity. In the end I went with diesel which hasn't disappointed and I was able to find the spec I wanted without any trouble.

I don't do a big mileage in the car circa 5k pa and provided you include some longish runs you won't have any dpf issues, MB seem very good in this respect compared to some other manufacturers mainly because their Diesel engines warm up very quickly. DPF purge usually takes place every 500-700 miles

 

[Yugguy]

Behave, there's literally 1000s of petrol vs diesel threads out there.
https://www.google.co.uk/search?as_..._occt=any&safe=images&as_filetype=&as_rights=

 

[Frontstep]

Why not have a few test drives.

 

[Ken_R]

Petrol for me every time. I only do about 4k mileage each year so MPG is not a consideration. Servicing for Petrol cars is (reputedly) cheaper.

And I couldn't be arsed with, every time you fill up, you'd have to look around for plastic gloves before handling the the Diesel pump.

Many moons ago, I had a Pug 206 Diesel as a replacement car. Six speed, but I was forever having to change gear. The 'power curve' on a Diesel is more constricted than that of a Petrol engine. Hence more gear changes. With an Auto, the driver probably wouldn't notice but, the gearbox would be making more changes than with a Petrol engine.

Would such wear parts of the gearbox greater than with a Petrol engine, or would such wear be carried over a greater number of gears/components, and therefore of little/no significance?

I really don't know the answer.

 

[geraldrobins]

Petrol for me every time. I only do about 4k mileage each year so MPG is not a consideration. Servicing for Petrol cars is (reputedly) cheaper.

And I couldn't be arsed with, every time you fill up, you'd have to look around for plastic gloves before handling the the Diesel pump.

Many moons ago, I had a Pug 206 Diesel as a replacement car. Six speed, but I was forever having to change gear. The 'power curve' on a Diesel is more constricted than that of a Petrol engine. Hence more gear changes. With an Auto, the driver probably wouldn't notice but, the gearbox would be making more changes than with a Petrol engine.

Would such wear parts of the gearbox greater than with a Petrol engine, or would such wear be carried over a greater number of gears/components, and therefore of little/no significance?

I really don't know the answer.

I disagree on the gear box issue and is not my experience at all. The reduced power band is usually compensated by higher overall gearing, and the higher torgue but at lower rpm makes gear changing less necessary at lower speeds.
If driving for maximum performance all the time you may have a point though.

 

[brianbrian]

I have to say glad MB don't put the diesel engine in the CL and SL range...But why don't they?

I have a 129sl with a Diesel engine 40 plus to the gallon, very reliable, enjoyed it for the last eight years.

 

[Noelmc]

Diesels are smelly dirty engines that need a huge amount of tech to work with "pollution limits" and even then they have been sold on a lie. Witness the VW debacle, and the other engine manufacturers are not far behind, in real life they pollute like f**k
They will be banned from most cities within the next decade. I'd stick to petrol until electric cars become economic.
Even the hybrids they are selling are based around the flawed tests that cars are subjected to, is it any wonder the batteries only last as long as the test do?
Test drove a Tesla earlier this year, now that is the future.
(I must state an interest, I drive a 5litre V8 petrol)