Diesel vs. Gas Engines
Initial Cost
Advantage gasoline.
Because of the high compression ratios and resulting high cylinder pressure found in diesel engines, diesels must be built to withstand more punishment than gas engines.
Beefed up parts include a thicker block and cylinder heads, and stronger connecting rods, pistons, crankshaft and valves. These parts can be costly.
Fuel Economy
Advantage diesel.
Diesel fuel has a higher energy density than gasoline. One gallon of diesel contains approximately 147,000 BTUs of energy, while a gallon of gasoline only has 125,000 BTUs. This means that it takes more gasoline to equal the power output of diesel, making diesel engines more efficient per gallon of fuel burned.
Because diesel engines use the more efficient direct fuel injection method compared to the port fuel injection setup used in gas engines where gas is mixed with incoming air in the intake manifold, the diesel system has very little wasted, or unburned fuel.
Diesels also use about 1/3 as much fuel at idle as gasoline units. Even though there are no official EPA mileage figures for 3/4-ton and bigger trucks, we've seen diesels get 6-8 more mpg than similar weight gas pickups. Over the life of the truck, this advantage could be significant, especially if you drive a lot of miles.
Short Term Maintenance
Advantage gasoline.
Regular maintenance on a diesel is more costly thanks to several items, including the larger volume of oil in the engine, and the fact that fuel filters and water separators need to be serviced more often. Modern gas engines have an even bigger advantage thanks to extended service intervals on things such as spark plugs, engine oil and antifreeze.
Long Term Maintenance
Advantage diesel.
The flip side of a diesel engine's expensive initial cost is its excellent durability. Dodge, Ford and GM learned long ago that they were better off buying diesel technology from experts such as Cummins, International and Isuzu than spending tons of money developing it themselves.
These manufacturers all have years of experience building heavy-duty, over-the-road diesels that have to log 100,000 miles a year for years on end, routinely haul heavy loads and may have to idle for days at a time. Think of the diesel engines found in GM, Ford and Dodge pickups and SUVs as mini big-rig engines.
The average gas engine is only good for around 125,000 miles before needing a rebuild and isn't designed to constantly pull a heavy load. A diesel can go more than three times this amount before needing an overhaul.
Conclusion
Choosing between a gas and diesel engine really comes down to what you'll do with the truck and where you live.
If you use your truck like a car, desire quick, quiet acceleration, rarely haul a heavy load and you don't plan on keeping it past 100,000 miles, then you may want to consider a gas engine. They run smoother, fuel is easier to find and they're easier to start in cold weather.
However, if you use your truck for towing, value good fuel economy, and plan on racking up loads of miles, then a diesel is for you. In the end, the leading disappointment regarding diesels is that the price to add a diesel to a 3/4- or 1-ton pickup is still quite high versus a more powerful gas engine. But, you'll make this back in fuel savings over time.