Yes, it is very bad to your engine. Your engine will be heat soak and your engine oil will be degraded faster than normal, thus reduce the protection. Besides, it will accumulate more carbon in your exhaust system, because there is no loading when the car is station. Even your radiator hose and all the rubber components inside the engine compartment will be soaking in the heat and caused damage sooner than normal usage. Do you feel that your car always feel more lethargy whenever caught in a bad traffic jam?
Most important is this will contribute to global warming! With the engine idling, it generated additional heat and produce carbon monoxide, not only consume additional natural resources like oil. Everyone should turn off their engine if they are waiting for more than 1 minute in the car park. This will not only save you money, it is also responsible to our mother nature. Something you might also want to consider, this is also a safety precaution because you do not know whether there is any leakage in your exhaust system that might leak the carbon monoxide into your car cabin, and the result can be fatal over long period!
Last word of advice, leaving the engine running in the car park for long period (I can not remember exact timing, could be 5 minutes) is actually against the law. The NEA officer can summon the driver for polluting the environment.
So there are more cons than pros. Let's do the right thing by switching off our engine whenever the waiting is more than 1 to 2 minutes. We can always wind down the windows for better air circulation, park our car under the shade, or even get out of our car and wait at nearby shaded areas.
I hope everyone can adopt the right practice and make our world a better place to live.
