I noticed a bad odor when passing lately and took my 740 to the mechanic twice. The mechanic said that he does NOT think it is the heater core. He advised us on getting the inside detailed thinking that we may have tracked something in on our feet. I got the car cleaned today but when I passed a car, the smell came back, not as bad as it had been but it was clearly there. It smells to me like biology class when we were disecting frogs (formaldehyde?) but my husband thinks it smells like antifreeze (which is what made us think it was the heater core). Our mechanic, on the other hand, thinks it smells like a mixture of cow manure and baby diaper. I neither live on a farm nor have a child in diapers. I'm not sure our mechanic has ever really smelled the odor since it happens when passing and I don't know if he has driven it out of the city. Does this sound familiar to anyone? I would very much like to find the culprit and rid my car of it forever. Thanks!