Disputes about how long it is permissible to keep the engine running while stationary have been going on for years. Some drivers claim that after just five minutes of idling, the engine begins to "die": supposedly, coking and accelerated wear appear. Others cite taxi drivers and truckers who may not turn off the engine for days in winter — and their cars still travel 400–500 thousand kilometers without any problems.
The truth, as usual, lies not in extremes. To understand it, it is worth separating established garage legends from real engineering logic.
The Myth of Oil Starvation
One of the most common fears is related to the assertion that oil pressure drops in the engine at idle and oil starvation begins. This thesis has long been passed from conversation to conversation and is often presented as an axiom.
In practice, this is not true for a working modern engine. The performance of the oil pump is designed by engineers with a significant margin. Even at a standard 700–800 rpm, the pump steadily pumps oil through all channels of the lubrication system. The crankshaft, camshafts, and other loaded elements are constantly in an oil bath.
If "dry" friction really occurred at idle, engines would massively fail in city traffic jams. This does not happen. From the point of view of mechanics and lubrication of friction pairs, prolonged standing with the engine running is not dangerous — even for an hour or two.
Where the Real Harm Lies
The key problem of idling lies not in mechanics, but in chemical processes. While the car is stationary, the mileage does not increase, but the engine continues to run. At this moment, operating hours accumulate.
The oil oxidizes, the additive package is gradually used up, and fuel combustion products accumulate in the system. As a result, with frequent and prolonged stops with the engine running, relying solely on mileage when changing the oil is a serious mistake.
For example, in 10,000 kilometers of city driving, the engine can work as many hours as it would accumulate in 20,000 kilometers on the highway. In this mode, the oil loses its properties much earlier than the regulated period, turning either into a too liquid substance or, conversely, into a thick mass.
If the car regularly idles or spends most of its time in traffic jams, it is reasonable to reduce the oil change interval by one and a half to two times. A more accurate guideline is 250–300 operating hours, not the numbers on the odometer.
Fuel and Engine Type Matter
The consequences of prolonged idling largely depend on what fuel the car runs on and how the injection system is designed.
Gas (propane or methane) is considered the most gentle option. It burns almost without forming carbon deposits. When running on gas, the engine can be at idle for a long time, remaining relatively clean inside.
Gasoline requires a more careful approach. With distributed injection (MPI), where the injectors are located in the intake manifold, contamination occurs slowly: the injectors are constantly washed by the fuel mixture. In systems with direct injection (GDI, TSI and similar), where the injector works directly in the combustion chamber, the situation is more complicated. At idle, combustion is less efficient, which is why the nozzles become covered with carbon deposits faster.
Diesel engines are by their nature "cold". At idle, they warm up poorly, the fuel does not burn completely, and the formation of soot increases. Modern diesels with particulate filters are especially sensitive to prolonged stops: the filter becomes clogged, and without load, the system cannot start an effective regeneration. At the same time, serious deposits in the engine itself, as a rule, appear only on mileages far beyond 100 thousand kilometers.
A Simple Remedy Against Carbon Deposits
It is impossible to completely eliminate the formation of deposits — this is a natural side effect of the operation of any internal combustion engine. However, with frequent driving with prolonged idling, there is a simple prevention that does not require costs.
At least once a week, it is useful to go to a highway or a free section of the road and let the engine run for 15–20 minutes at speeds of about 3000–4000 rpm. In this mode, the temperature in the combustion chamber increases, and loose carbon deposits burn out and are removed through the exhaust. This has a beneficial effect on the condition of the spark plugs, piston rings and catalytic converter.
The operation of the engine at idle does not in itself destroy the "iron". The price of comfort is not in the accelerated wear of mechanical parts, but in the faster aging of engine oil.
In the cold season, it is more reasonable to let the engine run for 10–15 minutes in place and start moving with warmed oil and normal thermal clearances than to immediately load a "frozen" engine. With this approach, it is only important to observe three conditions: reduce oil change intervals, use high-quality synthetics and regularly give the car a load on a free road.