Are diesel engines more reliable than gasoline engines?

I was watching a video about the US military adopting the JLTV to replace some of its Humvee fleet.

Being a military vehicle of this sort reliability is an important design feature. They said it was using a diesel engine.

I thought that was odd since diesel fuel is a lot less common than regular gasoline. I get these vehicles are not pulling into the nearest BP gas station to fuel up but still…regular gas stations are everywhere and, in a pinch, they could make use of them. Instead, they will need diesel fuel brought to them (or find a fuel dump).

Also, I thought diesel engines have real problems starting in cold weather. I remember sitting in my friend’s car holding a plunger in the dashboard out for a long time to get a glow plug glowing before you could start the diesel engine. I realize modern diesel engines are much better about this but still…(when I went skiing with my ski group the bus would leave its engine idling all night because starting a cold diesel engine was such a problem).

Is diesel really the best choice for a vehicle which is meant to be general purpose and could end up anywhere? Only thing I could figure is the diesel engine was simply more durable/easy to repair and that was enough to recommend it.

I believe Diesel engines can run on jet fuel in a pinch. Also, many military vehicles have Diesel engines – including HMMWVs, though there are gasoline-powered ones too.

In the US Army, as of 20 years ago, ALL the tactical gear ran on JP8, generators, humvees, trucks tanks aircraft boats. It was the occasional civilian TMP car or van that ran on gasoline (oh and lawnmowers ran on “mogas” mixed fuel/oil).

JP8, while having some similarities to diesel, is NOT (as any fueler will tell you) in fact diesel. As a former mechanic, I can tell you that in order to run on deisel all those trucks tanks humvees and generators need several adjustments, tuned, if you will, to run on diesel.

Well, what is JP8? You ask? Jet Petroleum 8, or so the fuelers would say. Sounded ok to me so I never questioned it.

Woops forgot to answer the actual question. The reason the US military uses “diesel” instead of gasoline is because it’s less volatile. Safer to transport large quantities in bulk, less explosive when getting shot at. You gotta work pretty hard to get diesel to burn compared to gasoline

I’m puzzled by this - I can’t remember ever seeing a gas station where diesel was not available?

Although googling, I’m astonished to discover how few cars in the U.S. are diesel. 3% vs 50% in Europe. I guess most of the diesel in the U.S. is used by trucks.

There are several reasons that militaries worldwide use diesels.

One is the significantly lower flammability of the fuel diesel engines run on- gasoline fueled tanks and vehicles have a tendency to catch fire very easily relative to diesel powered ones.

Second is the fact that in general, large engines are almost all diesels. So your armored vehicles, heavy trucks, bulldozers, and all sorts of assorted heavy equipment are going to be using diesels anyway. US M1 Abrams tanks use gas turbines, but they’re the exception to that rule; most other countries’ tanks use powerful diesels to get similar performance- see Germany’s Leopard II, Britain’s Challenger series, France’s LeClerc, and the Russian T-90 for examples.

Third is that logistics is significantly eased if everything uses the same fuel. JP-8 is what the US military uses for diesel vehicles- it’s basically Jet-A with anti-icing and anti-corrosion additives. It’s similar to kerosene, which is a little lighter than regular #2 diesel. They run fine on it, and everything uses JP-8 these days- tanks, helicopters, trucks, HMMWVs, and so on, which is the point- the logistics units only have to move one type of fuel for everything.

The only diesel car options in Canada were European - mostly VW, MB, and BMW - and the diesel emissions scandal pretty much killed the small market here.

These days it is rare to see diesel available in a gas station in the US but that can vary by where you are. Gas stations near a highway will likely have a diesel pump. In the middle of a big city…a lot harder to find one.

I obviously just haven’t been paying attention, because I have never driven a diesel car in the U.S. As you suspect, my awareness of diesel is entirely from dual price gas station displays on highways, and I suppose I just always assumed there was at least one diesel pump at all gas stations as there is in other countries.

Anybody remember the awful 5.7L/350 in^3 diesels manufactured by Oldsmobile, used in large GM cars from the late '70s-early '80s? It was so bad that it prompted many states to pass “lemon laws”.

I’m not in the military but I’m pretty sure when they deploy somewhere they bring everything they need with them, including food, ammunition, and fuel - plus - the means and intention to deliver/ration it out without relying on any local infrastructure. Doing so isn’t a weakness but a feature of the system… if you’re relying on scavenging local basic supplies either something went very wrong in the field, or you shouldn’t have gone in there in the first place.

Every gas station I see has Diesel fuel.

Diesel engines tend to be more efficient at converting fuel into motion, but only at certain RPMs. For something like a tractor trailer hauling freight, a diesel engine will easily outperform a similar gasoline engine. Similarly, a diesel car driven mostly on the highway will outperform a gasoline car.

Around town though, it’s generally the opposite. Since you aren’t using the diesel engine in its “sweet spot”, the gasoline engine tends to outperform it.

With modern diesel and gasoline engines (and transmissions), the difference isn’t as pronounced as it used to be, and in some cases the diesel can even beat the gasoline engine around town.

Diesel engines also have a disadvantage that they don’t like to start when they are cold. I have to plug my diesel pickup truck in during the winter.

Diesel engines have lower gaseous emissions than gasoline engines, but much higher particulate emissions. If you look at an old diesel engine’s exhaust, it looks like it pollutes more, even though overall it is polluting less, because you can easily see the diesel’s soot but you don’t easily see the gases that the gasoline engine emits.

Diesel trucks are the standard in the U.S. because of the cost/mileage difference, but diesel cars were a rarity until recently. Part of the problem is the narrower power range of diesel. Not only are diesels less efficient around town, but they tended to have much more sluggish acceleration with older transmissions. Also, even though their overall emissions are less, the higher particulate emissions make them seem “sooty”. Earlier diesel cars also tended to be noisier than their gasoline equivalent. This gave diesel cars a reputation for being noisy, sluggish machines that spewed black smoke wherever they went.

With better technology, most of that isn’t an issue any more. With a modern transmission, a diesel car is no longer sluggish, and the fancier transmission is able to keep the diesel engine in its power range a lot better, which increases diesel’s efficiency around town. All of the diesel cars that I have driven have been downright peppy, weren’t any noisier than their gasoline equivalents, and did not spew clouds of black smoke wherever they went. And since younger drivers don’t remember the sluggish, smoke-spewing beasts of the 70s, diesels are starting to lose their bad reputation and are becoming more popular.

VW didn’t do diesel cars any favors though with their fraudulent emissions tinkering. A lot of folks don’t trust diesels because of that mess.

As for Europe, there are a lot of reasons that Europeans prefer diesels for cars. Europeans have smaller roads and therefore drive smaller cars, so Europe never had those big clunky smoke-spewing diesel cars of the 1970s that gave U.S. diesel cars such a bad reputation. A major part of it though is taxes. A lot of countries in Europe tax vehicles based on engine displacement, and you get the most bang for your buck (or the most bang for your cubic centimeters) with a turbodiesel.

As for reliability, it’s hard to get an apples to apples comparison. Even if you compare the old Oldsmobile 350 diesel to the old Chevy V8 in cars that used both engines, it’s not an apples to apples comparison because the diesel engine had some design flaws that made it much less reliable for early models. Once they got the kinks out of it, the Olds diesel was actually very reliable. But that’s a classic example of a diesel being less reliable than its gasoline equivalent. On the other hand, there are numerous examples of diesel engines being more reliable than gas engines in other cars.

Part of a diesel engine’s reliability though often comes from the fact that they use thicker cylinder walls, heavier crank shafts, sturdier valves, and just generally more robust parts. If you designed a gasoline engine with similarly stronger parts, it would be more reliable too.

Often, a diesel is used in an application where ruggedness and high torque is needed, where a gasoline engine will be used in applications where the emphasis is on performance. This makes the diesels more reliable, because that’s what they were designed to be.

Diesels don’t like to start in cold weather, but it’s not as much of an issue as it used to be. I have to plug my pickup truck in during the winter so that the block heater keeps the engine warm, but if I forget there’s no fiddling with anything on the dash. When you turn the key it automatically activates the glow plugs, and you just have to wait a couple of seconds for the light on the dash to go out before starting the engine. If I have forgotten to plug the truck in during cold weather, I just turn the key, wait for the light to go out, then turn the key back off, turn it on again, wait for the light to go out a second time, then start the engine. The truck has never failed to start on me. While it’s true that a gas engine would just start up no matter what and also never needs to be plugged in at night, the diesel is nowhere near as fiddly as it used to be on older vehicles.

A friend had one. You’re right; it was awful. IIRC, he and his father replaced the diesel with a gas engine.

How do trucks fill up if diesel is rare?

I have a diesel car (Subaru Outback), it out performs my partner’s petrol powered Ford Focus for fuel economy in every area (town, open road, mix etc). Just one data point, I know.

“Rare” is relative and certainly there are places with diesel.

I live in Chicago and gas stations in Chicago rarely have a diesel pump.

But, if you are driving a truck, you are not filling in a gas station in Chicago.

Highway stations almost always have a diesel pump. That said, they probably have only one diesel pump while having a dozen gasoline pumps. (If they have a truck fueling area, and many do, that is likely reversed.)

How does diesel fuel compare price-wise?

Sometimes higher than gasoline, sometimes lower. Doesn’t seem to be any pattern to it, at least not around here (southern PA).

As a rough approximation, fuel prices tend to reflect the effective energetic content. However local taxes and logistics can overwhelm things. Oil and gas are internationally traded commodities, and in the end price reflects bang for buck in a pretty close manner. Diesel can command a slight price premium because, in general, it delivers better efficiency in the engines it is used in.

Diesel engines can be made to run on nearly anything in a pinch. They may not be totally happy, and may not give full power, but they will run. Ships run on stuff so thick they have to heat the tanks and feed lines to make the stuff flow. Making old cooking oil suitable for use in a diesel isn’t hard. The exhaust smells like fried potatoes.

It used to be that restaurants would just toss out their old cooking oil. Then folks realized that it wasn’t that hard to run a diesel vehicle off of it. The restaurants used to give it away for free to these folks since it saved the restaurant money (they didn’t have to pay to dispose it). Then the demand got so great that the restaurants started charging money for it. So the days of free fuel are unfortunately gone.

There are two basic approaches to this. One is to modify the fuel, the other is to modify the vehicle. If you don’t do either then the cooking oil will freeze solid when it gets cold and your diesel vehicle isn’t going anywhere.

Modifying the fuel is easy and can be done at home. You heat up the oil, add methanol and a catalyst to it, stir it up and then let it settle. The glycerin will settle out and poof! You have biodiesel that won’t congeal when it gets cold.

Modifying the vehicle isn’t that hard either. All you need to do is add a second small fuel tank, and a switch so that you can switch from one to the other. You put your cooking oil in the big tank, and diesel from ye ol local gas station in the small tank. You need some way of heating up the big tank, so most folks route the heat from their exhaust to the tank to thaw out the cooking oil for when it has congealed. You operate the vehicle by starting on the small tank of diesel, then switch over to to the big tank of cooking oil once everything has heated up. You have to be careful to switch back to the small diesel tank before shutting the vehicle off, and let the engine run long enough to get all of the cooking oil out of the fuel lines so your fuel lines don’t clog. A lot of people who do this try to switch over to the cooking oil before everything is fully heated, and they end up with carbon deposits in their engine due to the cooking oil being too cold and clumpy and not fully burning during engine combustion. As @Francis_Vaughan said, the exhaust smells like fried potatoes. With this method though, other than straining any french fries or food bits out of it, you don’t need to do anything to the oil. Most diesel engines run perfectly fine on unmodified used restaurant cooking oil.

Not disputing what you said, but as always Emissions are nuanced :

  1. NOx Emissions : Higher the engine combustion temperature, higher the efficiency (simple thermodynamics). Higher the Combustion temperature, higher the NOx.

So if you have engines without emissions control, the Diesel engine will produce more NOx. With emissions control (like catalytic Converters), both engines have equal emissions

  1. SOx emissions : Sulfur emissions are pass through - i.e. an engine doesn’t make sulfur, whatever sulfur is in the fuel, shows up in the exhaust. Depending on where you are in the world, you have have Ultra Low Sulfur Diesel or high sulfur diesel.

  2. Greenhouse Emissions : Diesel engines emit Black Carbon (soot or Particulate matter). Black Carbon has about 3000 times greenhouse gas potential as CO2 (Figure 2 https://www.smartfreightcentre.org/pdf/GLEC-BlackCarbonMethodology-SFC-Sep2017.pdf).

Two studies, I am aware of, point towards Diesel engines having far bigger greenhouse gas footprint, despite their efficiency
I. " Despite lower carbon dioxide emissions, diesel cars may promote more global warming than gasoline cars" - Despite lower carbon dioxide emissions, diesel cars may promote more global warming than gasoline cars :10/02).

II. Europe’s car fleets have been persistently transformed from being petrol-driven to diesel-driven over the last 20 years. …We conclude that global warming has been negatively affected, and air pollution has become alarming in many European locations.