Diesel vs petrol engines?

S

Snortan

New member
There was a car thread but don't want to necro it:) so here is a question for all the car enthusiasts, what are the main advantages and disadvantages of a petrol vs diesel engine?

I'm helping a friend buy a car but neither of us is that knowledgeable about them.
The car is most likely gonna be made before 2005, saloon body, engine size around 1.9.

Also is there any noticeable price difference between parts of the two when having to do repairs?
I always used to hear that petrol engines are hard to start on a cold morning, but UK is not that cold imo, would it still apply?
What else should I keep in mind ?
 
simply put..
diesel have higher torque so can go up hills, tow things easier, and are harder to stall.
petrol tend to have a higher top speed and better acceleration so are better for over taking.

then diesel work with compression. where as petrol works with a spark. (diesel is combusted by the pressure of the pistons causing it to combust. petrol uses a spark to ignite the fuel)
In generall terms these days they are very similar. they use injection and so on. most will have some sort of turbo, but both can go without.
Diesel will need a better battery with higher cranking amps.

then you have heater plugs in a diesel that is used to warm up the fule in the cylinders so it can start easier.
where as petrol uses spark plugs..
Spark plugs will need replacing more often than heater coils in general..

a diesel engine is less susceptible to issues due to water entering the engine bay. but honestly these days without distributors petrol cars dont really have the issue either.

On avarage. a diesel car will use less fuel per mile than a petrol car due to the torque. however a small diesel engine is probably less efficient than a larger petrol engine as you would have to smash the throttle to get the acceleration out of the diesel.
but generally if you have the correct sized diesel engine for the weight of the car it will be more efficient than the correct sized petrol engine for the size of the car.

hope that helps some.

p.s

these days a petrol engine would not be that difficult to start on a cold day. however a diesel engine with a slightly flat battery would be more difficult to start on a cold day compared to a petrol car with the same slightly flat battery.
As for the price of parts..

thats much more of a car on car basis..
a petrol ferari would be much more expensive to get parts for than say a diesel land rover. but the land rover is probably more expensive than a petrol golf.. and the petrol golf may be more expensive than a diesel mondeo..
 
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I don't know how taxes work in your country, but in ger you have to pay more taxes for a diesel car, in turn diesel is less expensive to buy and usually more efficient. Petrol fueled cars are usually quicker and generally sound better if you are into that sort of thing.
Hence, if you don't drive much or want to have fun with the car -> Petrol
If you travel a lot, mainly on highways -> Diesel
 
Diesels tend to resell better for equivalent mileage to petrol.

FYI, people are quoting nowadays but OP is looking at cars pre-2005, is that nowadays?
 
in terms of how engines work.. 2005 is still well post injection as standard.. so i think the basics lay'd out are accurate enough.
if we were talking early to mid 90's " and sooner" then there would be considerable differences that needed to be mentioned.
 
I don't drive but remember seeing somewhere that Diesel engines have less wear and tear so last longer, not sure if true just something I saw
 
Thanks guys! Appreciate the long post!
shambles1980 said:
in terms of how engines work.. 2005 is still well post injection as standard.. so i think the basics lay'd out are accurate enough.
if we were talking early to mid 90's " and sooner" then there would be considerable differences that needed to be mentioned.
Click to expand...
I had a chat with him and he says something between 2000 and 2005 due to them not being that expensive, so I guess everything you said still applies?

Any ideas on a make/model that is easy to maintain? His current one is a VW Passat from 2000 and any time something had to be changed we've done it ourselves, plenty of guides on youtube/google and it wasn't that hard or complicated, it was fun honestly so ideally with the new one we'd do the same instead of letting a shop do it.
 
I'd look at another passat tbh. A volvo is also another option too. If you're feeling a bit brave (not that they are too hard to work on) you could get a BMW 3 series for cheap. If you shop around for a while you'll find a good car. I have a bmw e46 coupe and its reliable, comfy and quiet. its a small engined model so its actually only a few mpg off my old Corsa.

The car thread isn't THAT old is it?
 
Diesels also give much better fuel economy than petrols. If you need a reliable workhorse that just keeps on going and going and is economical, a diesel makes sense. But if you want performance, high revs, and top end power, then you want a petrol.
 
Diesels are more efficient and have better torque (hence trucks use them) They tend to rev lower as the max Torque is produced quite low in the range. Great for towing and acceleration. HP is for show - Torque wins races. Of course most of them have turbos which helps a lot. If you're going 2005 watch out for emissions. They can get really dirty black smoke and sound like an old bus.

I drove an '06 1.4 Audi A3 TDI (diesel) a few years ago and I've just today got back from a holiday where I hired a 2016 1.4 Golf 90 Tsi (petrol) and for the engine size the Audi was punchier (accelerated quickly with little lag) and the Golf was more revvy and fun to drive. What can I say I like to wring it.

All in all though - they're both really good engines. Just make sure you buy one that's well maintained.
 
It seems like a diesel engine would be the better choice, he's going to use it for work too, just carrying some tools and stuff like that.
I'll point him towards this thread and see maybe he has any other questions.
 
When I was a taxi driver I bought a 1.6 petrol engine after workng out the overall running costs per year, whilst the diesel certainly returned more miles to the gallon the other running costs were much more
 
shambles1980 said:
As for the price of parts..

thats much more of a car on car basis..
a petrol ferari would be much more expensive to get parts for than say a diesel land rover. but the land rover is probably more expensive than a petrol golf.. and the petrol golf may be more expensive than a diesel mondeo..
Click to expand...
If you were to take the same car, roughly same engine size, any that you're familiar with, and if you were to compare repairs/running costs, which would be higher petrol or diesel and why if you can?

RobM said:
When I was a taxi driver I bought a 1.6 petrol engine after workng out the overall running costs per year, whilst the diesel certainly returned more miles to the gallon the other running costs were much more
Click to expand...
How did you do the math? I'd like to know what we're the costs for both
 
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As a professional opinion (Mechanic), there are pro's and con's to both sides. There is an age long debate over petrol vs diesel.

Personally, I like both for different reasons. But the winning argument is almost always down to economy. Diesel engines are far more economical to run. Look for a decent sized turbo diesel with no smoke and you are onto a winner for economy.

I'm assuming you are UK based, so be aware that tax for any vehicle registered on or after 1 March 2001 is based on emissions and you can be stung for higher Tax rates easily if you don't check first.

Beware of high mileage turbo diesels as turbos can be a very expensive repair. Every car comes with some expense when you are looking at 10 years plus vehicles. Make sure you check any car thoroughly for both mechanical and electrical issues.
 
The most important thing with a diesel engine is oil and filter changes MUST be done regular they are not as forgiving as petrol, if you drive short distances petrol is the way to go if you drive longer the diesel will serve better but that being said if you do drive the diesel short distances mostly you can avoid troubles by taking it for a long drive once a fortnight along a motorway or freeway whichever you have in your country to get everything nice and hot and blow out any excessive carbon
 
Avoid any car that is labelled as a "city diesel", such as 1.1 or 1.4 sized engines. Diesels are really meant for the reasonably long drives in order to give their efficiency. There was a raft of these city diesel car being borked by DPF failure (diesel particulate filter) getting blocked because they had never gone above 50mph. The solution is to go for a blatt and clear the exhaust system of all the crap.

If you're doing the maintenance yourself I'd say petrol as it's easier and cleaner to maintain.
 
It depends on the budget he is spending.

Cars of that age will tend to have high milage, making diesels more of a gamble.
Another question is what journeys is it being used for ?
Short hops i would go for a petrol.
Long runs can bring the diesel back as a choice.
Dmf (dual mass flywheel) will be fitted to most diesels of that age, only recently have petrols had them fitted.
The cost of the parts (dmf) is not to bad, its the labour for the tame spanner man to get to it.

I would stick to something mainstream, ford, vauxhall etc as parts will be readily available, plus should have a good selection to choose from in your area.
 
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