Why are there oil stains on the car chassis but no oil on the ground?
2 Answers
Oil stains on the car chassis but no oil on the ground may indicate oil leakage. Below is a partial introduction about the car chassis: Definition: The car chassis consists of four parts: the transmission system, the running system, the steering system, and the braking system. The function of the chassis is to support and install the car engine and its various components and assemblies, forming the overall shape of the car, receiving the power from the engine, enabling the car to move, and ensuring normal driving. Function: The power generated by the car engine is transmitted to the driving wheels through the transmission system. The transmission system has functions such as deceleration, speed change, reversing, power interruption, inter-wheel differential, and inter-axle differential. Working in conjunction with the engine, it ensures the normal driving of the car under various working conditions and provides good power and fuel economy.
The other day when I was washing my car, I also noticed an oil stain on the undercarriage, but the parking spot ground was completely clean. This situation is actually quite common—it's usually caused by slow oil seepage due to aging sealing gaskets or oil pan gasket wear. When the oil seeps extremely slowly, it clings to the undercarriage guard plate or bolts, forming sludge that doesn’t even drip onto the ground. Last time with my own car, it was the transmission vent valve leaking, leaving dark, sticky oil stains on the exhaust heat shield. If you’ve just had maintenance, it could also be from an oil filter not tightened properly or a reused drain plug gasket. I’d recommend using engine degreaser to clean off the stains first, then check the seepage point again after two weeks—this way, the mechanic can pinpoint the issue faster.
