Why are diesel engines considered more reliable than petrol engines.

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BurnitBlue

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I have always been told that this is because of the ignition system on a petrol engine is not waterproof and can fail at sea.

However, my neighbour who drives heavy trucks for a living said that diesels are much more reliable on the roads as well.

Any reason why, because this, to me, is anti-intuitive in that a diesel is more complicated than a petrol engine with higher compression, and complex fuel pumps and precise timing controls.

I am just curious.
 
I thing what people are saying is that on the whole diesel engines have a longer life providing they are looked after, take a HGV for instance, or a London Bus, 300,000 miles nearly non stop, imagine doing that in your family car.
 
I'm not that well up on it but I think petrol combustion products are more corrosive, at least in the exhaust system they are.
 
I think older diesels were def more reliable than older petrol engines esp in marine environments. They were also usually marinised car engines which doesn't help.

However in terms of reliability I'm not so sure these days, I'd presume them to both be much more equal.

I used to know an old fishing guy who swore rancid about outboards and loved his old perkins which was always going wrong (although seldom admitted).

My "new" Yamaha 150 o/b couldn't be more reliable or less problematic compared to the petrol and diesel engines of various ages I have experienced. This includes same year large diesels.

So IMHO it depends on age, although I do appreciate why there's other reasons people prefer diesel, but that's another matter.
 
For sure petrol engines suffer a relatively high degree of unreliability due to damp on the ignition. On the contrary, a diesel will run underwater as long as it has a snorkel. Beyond that, I think it's largely a question of durability rather than reliability. Traditionally diesels have been designed for lorries and other "industrial" applications whereas petrol engines have been designed for private cars. The needs and expectations of the end-user are very different and the result is that they get very different products.
 
I thought it was because the explosion within a diesel engine is much more violent, therefore the engine has to be built stronger to withstand the stresses.

Also, you don't have all that high tension stuff to go wrong.
 
BlueTwo said:
I have always been told that this is because of the ignition system on a petrol engine is not waterproof and can fail at sea.

However, my neighbour who drives heavy trucks for a living said that diesels are much more reliable on the roads as well.

Any reason why, because this, to me, is anti-intuitive in that a diesel is more complicated than a petrol engine with higher compression, and complex fuel pumps and precise timing controls.

I am just curious.
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No a Diesel is NOT more complicated. It is inherently simple. Most petrol engines have direct or indirect injection just like a diesel anyway these days and there is nothing more "precise" about it either! The lack of ignition systems is a big bonus, but both are inherently reliable these days. The main reason to avoid petrol engines on boats (apart from ignition systems) is you don't have to carry gallons of highly volatile fuel.
 
michael_w said:
I thought it was because the explosion within a diesel engine is much more violent, therefore the engine has to be built stronger to withstand the stresses.

Also, you don't have all that high tension stuff to go wrong.
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I'm never sure about that argument which was around a lot when cars were beginning to go diesel. I would assume that they'd both be designed against failure to the same safety margin. More convincing, I think, is that diesel fuel is inherently a better lubricant than petrol and so gives the top piston ring and the cylinder bores an easier time thus promoting longevity.
 
michael_w said:
I thought it was because the explosion within a diesel engine is much more violent, therefore the engine has to be built stronger to withstand the stresses.
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Yes, much stronger to survive higher compression and most are lower revving higher torque. The diesel is not as flexible a power source as a petrol engine so isn't as good for cars but is excellent for trucks and boats that tend to plod very long journeys at fairly stable speeds. Keep the stresses low, the revs low the speed constant the oil and fuel clean and the outside free from corrosion. Potentially limitless life (50 years +++) for the enthusiast who can do the pots valves and bearings every decade or so and send the injectors to a specialist when needed.

Petrol (gasoline) is a horrid solvent that washes oil off the cylinders, knocks, and other nasty things. Gentlemen prefer diesels.
 
Modern automotive diesel engines have electronic boxes for injection control and the injectors themselves are either solenoid or piezzo electric activated.They still are very reliable but the no electrics doesn't apply any more.
 
Some really good and logical answers above and thanks. So if as some imply, the gap between diesel and petrol reliability is getting narrow(er) will we see a return to petrol especially in race boats to save weight?

Looking at MOBO's it is significant that a diesel engine boat seems a lot more expensive than a petrol engine boat or have I got that wrong as well? Maybe that difference in boat prices is more to do with fuel consumption and Red Diesel fuel.
 
Don't forget diesels rev much lower than petrol engines, so a 250,000 mile diesel engine may have done the same total number of revs as a 150,000 mile petrol engine.

Also diesels are unthrottled. A petrol engine needs to be throttled to keep the petrol/air mixture constant (is it at about 14.5:1 ?) or it won't spark ignite, but a diesel just burns much leaner at low power as what we all call the "throttle" actually just controls how much fuel is injected and leaves the air unrestricted, and this, I believe, means the gases produced under those conditions are more "diluted" and hence less corrosive.
 
My preferance (depending on boat type) would be a diesel with prop (not stern drive) for a combination of reasons, but I'm also very happy with the new Petrol Outboards that are being produced today.
 
billcole said:
Don't forget diesels rev much lower than petrol engines, so a 250,000 mile diesel engine may have done the same total number of revs as a 150,000 mile petrol engine.

Also diesels are unthrottled. A petrol engine needs to be throttled to keep the petrol/air mixture constant (is it at about 14.5:1 ?) or it won't spark ignite, but a diesel just burns much leaner at low power as what we all call the "throttle" actually just controls how much fuel is injected and leaves the air unrestricted, and this, I believe, means the gases produced under those conditions are more "diluted" and hence less corrosive.
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Brilliant, but I am definitely getting out of my depth as the answers are more complex than I imagined. What I thought was a simple question has many, not so simple answers, and they all seem correct. So excuse me if I just read the posts from this point on.
 
One factor which no-one so far seems to have mentioned is that - provided you can start it - a simple yacht diesel does not need an electrical system in order to run. So a complete electrical failure does not necessarily render a vessel without engine power.
 
Just like to correct one bit ... posts here mention Petrol Engines usually based on car ... diesels not.

mmmmmm Perkins 4 series engines powered London Cabbies, 50's school buses etc. etc. as well as industrial stuff. Perkins were not only to do it. BMC - based on car engines like Marina / Montegos etc. Whole batch actually ...

Funny thing is many petrol engines were a lot smaller HP than the diesel replacements ... Vire 6 replaced often by Petter 12's etc. Never saw a car with small Vire or Dolphin engine ....

:D:rolleyes:
 
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