List of common mechanical problems that hurt fuel economy

[Phantom]

Bad fuel filter and stuck/dragging pulleys can kill mpg.

[Daox]

I'm bumping this old thread. Its worth a look through as its fall and working on cars during the winter isn't quite as fun as summer. Might as well get it fixed up now.

[bobdbilder]

After 12 years of useful life the airconditioning compressor gave out on me in a spectacular fashion. The whole compressor seized and the pulley stopped spinning while the engine still did. This caused smoky conditions in an underground car park. Finally the belt broke lose and I also lost power to the hydraulic pump assisting my steering. It was 2 days of hard driving but i gained great mileage. I had the compressor replaced but it showed better results than when I was using the old compressor. The bad compressor caused high parasitic loss at the pulley. It pays to look out for funny noises from the engine bay.

[cRiPpLe_rOoStEr]

Originally Posted by radioranger

I read that in WW2 some pilots found by running a bit less oil in their planes a good amount of HP was gained

That's because the oil in the sump still generates some drag that the crankshaft has to overcome. No wonder so many high-performance engines have been resorting to dry-sump lube systems...

[101Volts]

Some time ago Dad's 2000 3.0 Caravan had a sticking rear brake. I had difficulty getting the MPGs up beyond 20 on the ScanGauge II when it was like that, after it was fixed the MPGs went up by 2-4 at least. We also had low quality fuel a few times and it tanked the MPGs; gone from 24 to 16 - and that's not city driving, it's more rural and HWY driving.