In Summary
  • The Society of Automotive Engineers SAE have carried out several tests on the road and in wind tunnels which confirm that when driving at medium speeds use of AC decreases fuel economy more than opening windows does.
  • However when driving at higher speeds opening windows increases drag (air fluid resistance against moving objects) which creates a bigger load on the engine and reduces fuel economy more than AC does.

Hi Paul, is it true that turning on the AC when driving is better for fuel economy than driving with the windows open? Gabriel Mwanga

Hello Gabriel, it is widely acknowledged that running the AC on your car adds a load to your engine which causes a drop in fuel economy.

How much fuel economy is lost will depend on how big the vehicle is, how hot it is, the air conditioning technology (manual or automatically controlled), how well serviced the air conditioning system is (correct level of AC coolant and lubricant) or how efficient the technology of the car is.

What is not in dispute is the fact that running the AC as you drive does put a toll on the fuel economy. What is in dispute, however, is whether cooling with AC is more fuel efficient than cooling off with the wind from open windows as you drive.

The Society of Automotive Engineers SAE have carried out several tests on the road and in wind tunnels which confirm that when driving at medium speeds use of AC decreases fuel economy more than opening windows does.

However when driving at higher speeds opening windows increases drag (air fluid resistance against moving objects) which creates a bigger load on the engine and reduces fuel economy more than AC does.