Dangers of Cheap Diesel: Threat of Engine Deposits in Modern Diesel Machines

JAKARTA, KOMPAS.com - The recent rise in non-subsidised fuel prices, particularly for diesel, has prompted many diesel vehicle users to seek ways to reduce operational costs. As of 4 May 2026, the price of Dexlite in the Jakarta region increased to Rp 26,000 per litre from the previous Rp 23,600. Meanwhile, Pertamina Dex surged from Rp 23,900 to Rp 27,900 per litre. One common measure taken is to use lower-quality fuel, including subsidised Biosolar, or to mix it with non-subsidised diesel to keep refuelling expenses from becoming too high. However, it turns out that long-term use of low-quality diesel has the potential to accelerate the formation of deposits in modern diesel engines. A lecturer in Mechanical Engineering at Gadjah Mada University, Jayan Sentanuhady, stated that fuel quality greatly influences the combustion process inside diesel engines. According to him, using poor-quality diesel can impact vehicle performance decline, dirtier exhaust emissions, and more frequent maintenance needs. “If the fuel quality is not good, the combustion is also not optimal. The effects include reduced engine performance, worse emissions, and more frequent maintenance,” Jayan told Kompas.com on Thursday (7/5/2026). Deposits in diesel engines generally arise from incomplete combustion processes. Low-quality diesel typically has higher sulphur content, lower cetane number, or even contamination with water and dirt. As a result, combustion in the engine chamber does not proceed optimally and leaves behind carbon deposits. In the long term, deposits can accumulate in the injectors, pistons, valves, and EGR (Exhaust Gas Recirculation) channels. In modern diesel cars that already use common rail technology, this problem can be more serious. This is because modern injection systems operate at high pressure and with very precise component tolerances. When injectors start to get dirty due to carbon deposits, fuel supply becomes imperfect.