Petroleum vs. Diesel: Which vehicle is more suited for you?

by Mark Lorenzana

In the advent of rising oil prices, choosing a vehicle based on engine type (petrol or diesel) might prove to be a very wise decision. Each engine type has its own advantages and disadvantages and your decision on what to purchase might well boil down to the vehicle’s purpose (i.e. for city driving, for hauling cargo, for heavy duty use, etc).

Let us compare a petrol and diesel engine and see how they stack up against each other, based on the facts:

Fuel Economy
Diesel has a higher energy density than petrol. This means it takes more petrol to equal the power output of diesel, therefore diesel engines are more efficient per liter of fuel burned. Diesel units also use about one third as much fuel at idle as petrol units. Over the years, this advantage could be significant, especially if you drive a lot of kilometers.

Noise/Vibration
Despite huge improvements in engine-noise technology in the past 10 years, diesel engines are still generally louder and shake more than their petrol counterparts. At idle, the clatter and shake of a diesel vehicle is clearly noticeable, while it's tough to tell if the petrol engine is even running. Under low-speed acceleration, a diesel engine is still noisier.

Fuel Cost
Because diesel fuel is easier to refine, taking less time to get from crude oil to final product, it's usually priced lower than petrol.

Short-Term Maintenance
Regular maintenance on a diesel engine is more costly, due to larger volume of oil in the engine and because fuel filters and water separators must be serviced more often. Modern petrol engines have an even bigger advantage thanks to extended service intervals on spark plugs, engine oil, etc.

Long-Term Maintenance and Durability
A diesel engine has an expensive initial cost but the flip side is its excellent durability. The average petrol engine is good for only around 200,000 kilometers before needing a rebuild and isn't designed to constantly pull a heavy load. A diesel engine can go more than three times this amount before needing an overhaul.

Exhaust Smell/Emissions
Despite oil companies’ best efforts at producing diesel fuel with lower sulfur levels, burned diesel fuel still smells much worse than burned petrol. Beyond the smelly tailpipe, diesel lags behind petrol in the areas of Nitrogen Oxide emissions.

Power/Torque
Petrol engines have the advantage in horsepower, while diesel engines produce more torque. By design, petrol engines rev faster and are able to reach higher rpm peaks than diesel engines. This allows them to attain greater horsepower numbers.
However, for towing capacity and pulling force, a diesel owns a petrol engine. The torque advantage of a diesel vehicle is suited for pulling heavy loads, even up steep inclines. Because of the relatively high-compression ratio necessary to ignite the diesel fuel (17:1 diesel versus 9:1 petrol), a diesel engine makes all its torque and power low in the rev range.

Conclusion:
As stated in the beginning of this article, choosing between a petrol or diesel engine comes down to what you'll do with the vehicle and where you live. If you want quick, quiet acceleration, rarely haul a heavy load, and you don't plan on keeping the vehicle past 170,000 kilometers, you may want to consider a petrol engine. However, if you are going to use your vehicle for towing, value good fuel economy, and plan on racking up loads of mileage, diesel is for you.


About the Author:
Mark Lorenzana is a fulltime copywriter for IBC Japan. He has written a regular column and articles for various newspapers and moonlights as a copyeditor and freelance writer.