What Causes High Fuel Consumption in Diesel Vehicles?

[SanValeria]

The reasons for high fuel consumption in diesel vehicles may include insufficient compression, poor atomization, and mechanical failures. Insufficient compression: The main cause of incomplete diesel combustion is insufficient compression, commonly referred to as air leakage. The reasons for air leakage include wear and tear of the cylinder liner, piston, and piston rings, leading to poor sealing, as well as valve leakage due to wear on the valves or valve seats. Poor atomization: This is mainly caused by aging of the fuel injector, plunger, or delivery valve, or improper adjustment of the injector. Mechanical failures: Incorrect fuel injection timing, clogged air filters, and restricted air intake can lead to inefficient engine operation, slow performance, and incorrect intake and exhaust valve clearances.

[DiStella]

After driving a diesel pickup for over a decade, I've found that sudden increases in fuel consumption usually boil down to these issues: First, aggressive driving habits—constantly flooring the accelerator and slamming the brakes, with engine RPM frequently soaring above 3000. Second, neglected maintenance—the air filter clogged up like a facemask, the diesel filter unchanged for half a year, and the fuel injectors blocked by debris. Third, driving on underinflated tires—tire pressure below 2.0 bar causing full tread contact, forcing the engine to work 30% harder. Last week, my truck had a leaking turbocharger hose, and I ignored the dashboard warning light—fuel consumption jumped from 8L to 11L instantly, but returned to normal right after the repair.

[ORiley]

The worst nightmare is when a diesel fuel system acts up! When the high-pressure fuel pump lacks sufficient pressure, the fuel atomization deteriorates, causing droplets to form and leading to incomplete combustion. If the injector gets stuck in the open position, it’s even worse—diesel leaks straight into the cylinders, and thick black smoke pours out. Once, after disassembling an engine, I found the EGR valve stuck open, causing excessive exhaust gas recirculation and lowering combustion temperatures—sometimes without even triggering a fault code, yet fuel consumption secretly jumped by 20%. My advice: clean intake manifold carbon deposits every 50,000 km—that sludge soaks up fuel worse than greasy pan residue.

[DeKimberly]

The key to diesel engine fuel efficiency lies in complete combustion. Insufficient cylinder pressure is the most common issue; when piston rings wear out, sealing deteriorates, leading to inadequate compression ratio and incomplete diesel combustion. Incorrect valve clearance can also cause air leaks, often sounding like a hissing exhaust. I've tested the same model, and those with SCR urea systems consume 5% more diesel than those without, due to excessive back pressure in the aftertreatment system. The worst is using cheap diesel from small stations in summer—excessive gum content clogs the fuel lines, causing the engine to roar without power and waste fuel.