What’s the Difference Between Gas and Diesel Truck Maintenance?

Diesel trucks are quite different from gasoline ones. That means home mechanics have to keep a few things in mind before wrenching on them. That’s in addition to the other considerations required for pickup truck maintenance. But diesel truck maintenance isn’t terrifyingly-complicated, as long as you keep a few things in mind.

Glow plugs, not spark plugs

Diesel trucks don’t need spark plugs. They run on compression-ignition, squeezing the diesel-air mixture until it heats up and explodes. The lack of spark plugs does make diesel engines easier to work on, and more reliable. Until, that is, it gets cold outside.

If the outside air temperature drops too low, the diesel can’t get hot enough to ignite. That’s why modern diesel engines come with glow plugs. Think of these as tiny space heaters or toasters. By warming the combustion chamber, they let the engine run even in the winter. Gem State Diesel recommends regularly inspecting your glow plugs, especially during the critical winter months.

Two batteries

Diesel trucks need a lot of juice to start. This is partly because of the glow plugs’ power draw, but mostly because of the compression-ignition system. The pistons have to squeeze really the incoming diesel-air mix really tightly, significantly more than in a gasoline engine. To make sure there’s enough power for everything, diesel trucks have two batteries.

Diesel exhaust fluid

Diesel trucks produce a lot of soot and NOx emissions. Soot in the exhaust is cleaned up by particulate filters (which coal-rollers usually delete). NOx gases, the ones that cause harmful smog, require something more.

Modern diesels use DEF to clean up their exhaust gases. A combination of water and urea, it’s injected into the exhaust gas stream. There, it reacts with NOx and air to turn the harmful gases into safer emissions. DEF does eventually run low, although according to Cars.com, many trucks can go up to 10,000 miles between refills.


As Car Talk explains, diesel engines are harder on their oil than gasoline engines. Diesel truck oil doesn’t just lubricate, it also cleans and cools. Because of all the soot diesels produce, these engines need both more oil, and more frequent oil (and oil filter) changes. Otherwise, Gem State Diesel warns, you could clog the engine and cause significant damage.

Because of the need to keep the engine clean, diesel truck oil contains more detergents and additives, says Oil Specifications. That, plus the quantities needed, raise the cost of the average oil change. But it’s a necessity to keep the engine running smoothly.

Fuel filters and water separators

Because of how diesel engines function, it is absolutely vital that only pure diesel fuel goes into the engine. If water got in, it could cause significant damage to the entire engine. Adding to the purity problem is the issue of the diesel fuel itself. Diesel combustion is inherently dirty, and even low-sulfur diesel carries more impurities than gasoline.

For these reasons, as CarID explains, diesel trucks have both a fuel filter and a water separator (also called a water filter). Every car and truck has a fuel filter, but a diesel truck’s fuel filter has to be replaced more frequently. As with the oil change, each manufacturer has its own fuel filter replacement schedule. And as for the water separator, PickupTrucks.com mentions that many new diesel trucks have a warning light for when it has to replaced.

Diesel truck maintenance has a few differences compared to gas truck maintenance. But now you know what to look out for.