What are the effects of overfilling engine oil in a truck?
4 Answers
The following are the effects of overfilling engine oil in a truck: 1. Reduced engine power output: Excessive engine oil can reduce the engine's power output. When the engine is running, the crankshaft and connecting rod big end move rapidly. If there is too much oil, the crankshaft and connecting rod will cause intense agitation. Agitating the oil consumes a certain amount of energy, which indirectly leads to a reduction in engine power output and also increases fuel consumption. 2. Excessive engine oil can cause blue smoke from the exhaust pipe: Too much oil will inevitably lead to oil splashing due to the rapid movement of the crankshaft and connecting rod big end. A large amount of splashed oil can enter the combustion chamber and burn, resulting in blue smoke from the exhaust pipe, also known as "oil burning," which is a method to determine excessive fuel consumption.
Let me make this clear. I've seen too many drivers thinking that adding extra engine oil is safer, only to end up damaging their engines. The biggest problem with too much oil is that the crankshaft will whip the oil as it rotates, churning it into foam—like whisking eggs. Once this foam enters the lubrication system, it's game over. Oil pressure fluctuates wildly, and precision components like bearings lose their stable oil film protection, leading to instant scoring. Even worse, the engine's running resistance increases, making it feel like dragging your feet—fuel consumption spikes while power drops. I once worked on a car spewing blue smoke; when we opened it up, the valve stem seals were all blown out. The repair cost was enough to buy two years' worth of oil. Remember, the safest level is between the middle and upper marks on the dipstick. If it's over, drain the excess immediately.
With over 20 years of experience in auto repair, nothing worries me more than improper engine oil filling. Overfilling oil is like force-feeding someone—when the oil level in the crankcase gets too high, the rotating crankshaft directly whips the oil. This not only needlessly saps engine power (making the vehicle sluggish) but also generates excessive foam. When this aerated oil enters lubrication passages, critical components like pistons and cylinder walls get starved of lubrication, causing visible scoring within just a few thousand kilometers. Telltale signs include weakened acceleration post-oil change and flickering dashboard oil warning lights. Recently, we handled a FAW light truck where an apprentice added 18 liters (16L required)—resulting in severe oil seal leaks, with the front crankshaft seal dripping persistently.
The most distressing thing about engine repair is seeing overfilled oil. The crankshaft splashing in excessive oil creates significant resistance, immediately increasing fuel consumption by 5%, not to mention the more dangerous issue of aerated oil. Foamy oil entering hydraulic lifters can cause valve noise, and if it gets into the VVT system, it may jam the timing adjustment. Last winter, a refrigerated truck suddenly developed unstable idle; inspection revealed it was 1.5 liters overfilled. The foam entered the PCV valve, froze, and caused a blockage, leading to excessive crankcase pressure that blew out the rear crankshaft seal. It's advised to strictly follow the manual's specified quantity when refilling—better to be 0.2 liters short than over.
