Why is the BMW's wading depth so low?
2 Answers
What affects a car stalling after wading through water are the air intake and exhaust outlets. As long as the exhaust outlet has sufficient pressure to expel water from the air intake, the car can generally pass through the water surface if the air intake doesn't take in water. In ordinary cars, the air intake is located above the filter, while in BMWs, it is below the filter, which is why the wading depth is relatively low. Typical sedan wading depth: Generally, the wading depth for sedans is around 20-30 centimeters because the exhaust outlet of an average sedan is about 20-30 centimeters from the ground. The method to determine wading depth is to observe the height of the exhaust outlet. Vehicle height is unrelated to wading capability: Some cars may appear tall, but upon opening the hood, the air intake is positioned quite low. For example, models equipped with turbocharged engines usually have lower air intakes, primarily to enhance cooling, which makes their wading capability weaker.
I've repaired quite a few water-damaged BMWs, and found their low wading depth is mainly determined by chassis design. Take luxury sedans like BMWs - for better handling stability, the body is intentionally lowered, which also brings down the exhaust pipes and air intake positions. The air intake sits near the front grille, so slightly higher water levels can directly flood it. Once repaired a 5 Series where the engine hydro-locked needing major repairs after just crossing a 30cm deep puddle. Moreover, its undercarriage has electronic modules dense as spiderwebs. While these components are waterproofed, prolonged submersion still risks short circuits. For actual wading, honestly I'd advise not exceeding half the wheel rim height.
