Q: Airconditioning system off before start & warming up the engine before driving

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Hi Mechanic,

I own a mercedes ML 350 from 2013. I have 2 questions!

1: Is it true that it's better for the engine of the car to start up the engine and idle it for 1-2 minutes before driving away? What about cold conditions? What about hot conditions, lets say summer temperatures of 25 degrees Celsius and up?

2: Is it necessary to turn off my fan and A/C system before shutting down the car? Also when I start up the car the A/C + fans should be turned off before starting as this is better for the engine/ car since the A/C compressor is directly connected to the engine.

This is what somebody told me but I think it's not true. Please provide an answer with an explantion.

Thank you much!

My car has an automatic transmission.

A: I always recommend allowing the car to run ...

I always recommend allowing the car to run until warm in cold or hot conditions. I wait for the engine to run until the idle hits the base idle speed (around 700-800 RPM) before driving it. This allows the oil pressure to build and the engine block to warm up before driving it.

Turning off all loads on the engine like the A/C system is better for the engine on start-up as well. The A/C system heats the condenser in front of your radiator and runs the fan, which creates a load on the engine. So in 25 Celsius, I recommend letting the vehicle idle for a few minutes to allow the cooling system to balance out and regulate engine temperatures. Rolling down the windows a little will give some air flow until you turn on the A/C.

You can prolong the life of your engine by allowing your engine to warm up without loads before driving it. It will also allow your transmission fluid to warm up to normal temperature.

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