What Causes the Loud Cold Start Sound in BMW 640gt?
3 Answers
Introduction to the reasons for loud cold start sound in BMW 640gt: Engine Carbon Deposits: The reason is that as old engine oil becomes thinner with use, carbon deposits accumulate more and more. Thinner oil is prone to leakage, leading to increasing carbon deposits and significant power loss. When new oil is replaced, the engine may not adapt to the oil's viscosity immediately, potentially causing higher RPMs and resulting in increased engine noise. Incorrect Engine Oil Specifications: Or excessive oil quantity. When there is too much oil in the engine, it creates unnecessary resistance to the crankshaft rotation, affecting power output and increasing fuel consumption. Carbon deposits in the combustion chamber, when red-hot, can also cause pre-ignition. Moreover, carbon deposits accelerate wear on cylinders and pistons and negatively affect oil quality. In summary, excessive oil increases the stirring resistance of the crankshaft and connecting rods, leading to louder noise.
I've driven the BMW 640GT for a while, and the sound during cold starts is indeed louder. This is mainly because, in low-temperature environments, the engine needs to warm up quickly to protect its components, so the RPM temporarily increases. BMW's design is quite clever—it lets the engine roar to heat up the exhaust to an ideal state. If you live in a cold region, this will be more noticeable on winter mornings. Don't worry, this is usually normal as long as the sound isn’t persistent or drastically louder. However, if the loud noise continues after the cold start, you might need to check for exhaust system leaks or see if the engine oil needs changing. Similar models like the Audi A7 may also exhibit this behavior. Regular maintenance and listening to experienced owners' advice will help you drive with peace of mind.
As someone who enjoys delving into cars, I've studied this phenomenon with the BMW 640GT. During a cold start, the engine control module increases RPM to accelerate catalytic converter warming and reduce exhaust emissions. The GT series' high-performance engines feature enhanced exhaust acoustics for a more sporty sound. This isn't a defect but part of the vehicle's intelligent optimization. However, if the sound is accompanied by vibrations or warning lights, potential component failures like exhaust manifold leaks should be ruled out. In daily use, avoiding frequent cold starts can reduce noise, and driving after warm-up is more worry-free. Compared to the Mercedes CLS, BMW handles this aspect more proactively. Ultimately, understanding vehicle mechanics leads to more confident driving.
