My C240 (M112) 2.6L V6 engine recently develops a strange noise when it is cold. As long as the engine operating temperature is below normal, the engine makes a vacuum-like (woooooo) noise when the car is traveling between 40km/h and 60km/h. The noise appears to be coming from the left side of the engine. The noise is more obvious or louder when the weather is colder. But once the engine reaches its normal operating temperature at 80 celcius, the noise disappears.

Also, when the engine is cold, I can feel the vibration from steering wheel when it is idling and when the transmission is in “Drive” mode. The vibration is transmited from the shaking of the engine when it is cold. I could also hear the engine makes this “duh-duh-duh-duh” noise when it is cold while idling with the transmission is “Drive” mode.

I took it back to dealer, and the dealer could not locate the problem. I appreciate for any invaluable inputs you give me.

Thanks,
Johf

2001 C 240X
54,000km (34,000 miles)