Why does the RPM increase after changing the engine oil?
3 Answers
Here are the reasons for the RPM increase after changing the engine oil: 1. The vehicle previously used winter engine oil, which has higher viscosity. This time, all-season engine oil with lower viscosity was used, resulting in reduced engine resistance and consequently higher RPM. 2. It is possible that counterfeit engine oil was used. Using counterfeit engine oil can cause significant damage to the engine, ranging from accelerated engine aging to complete engine failure. Therefore, it is essential to change the oil at reputable automotive maintenance facilities. Here is additional information: Engine oil, also known as engine lubricant (English name: Engine-oil), has a density of approximately 0.91×10³ (kg/m³). It serves multiple functions, including lubrication and friction reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion protection, and shock absorption. It is often referred to as the "blood" of a car. Engine oil consists of base oil and additives.
I've also experienced higher RPMs after an oil change, which is quite common. First, it could be due to the different viscosity of the new oil. For example, switching from old oil to a thinner oil reduces internal engine resistance, causing the ECU to briefly adjust the RPMs during adaptation. Alternatively, overfilling the oil can submerge the crankshaft, reducing additional resistance and increasing RPMs. Secondly, during the oil change, sensors or the air filter might have been accidentally disturbed, leading to unstable air intake and affecting idle control. Additionally, if you switched to a different brand of oil, inconsistent additives can trigger an ECU adaptive learning phase with fluctuating RPMs. It's advisable to immediately stop and check the dipstick to ensure the oil level is between the marks. Monitor the situation for a few days to see if it stabilizes; otherwise, quickly return to the repair shop to scan for trouble codes to avoid prolonged engine overload and part damage. Regular maintenance with the correct oil specifications is crucial.
Last time after I changed the engine oil, the tachometer was jumping up and down scarily. Later I figured it out: the new oil was too slippery, reducing friction, so the engine ran lighter and the RPM naturally increased. Or maybe the oil level wasn't adjusted properly - overfilling caused high pressure making idle unstable. Alternatively, during the oil change, some wiring harness connectors might have been accidentally loosened, causing ECU readings to go haywire with automatic RPM compensation. I later rechecked the oil level, ensured the air filter wasn't dusty, took a few drives to let it adapt, and the performance improved significantly. Oil changes are no trivial matter - buying the right brand and specification prevents issues. Otherwise, floating RPM not only wastes fuel but also damages the engine. Address it early to avoid long-term problems.
