I'm Stumped (Poor MPG)
 

Hi guys,

I thought I'd ask the forum before I break down and commit the ungodly act of paying someone else to work on my car.

I'm having issues with my r56 cooper s (N14). I recently moved from Colorado to St. Louis, and have noticed that efficiency of my car has fallen off a cliff. In Colorado I would struggle to get below 37.5 mpg, even while taking it on a few spirited drives through the canyons. Now that I'm here, even when I try to drive efficiently, I'm struggling to see 31 mpg on flat (by Colorado standards) highways. The service that I've done since owning the car (bought last July) has been pretty simple, just keeping up with oil changes, and I've installed the timing chain tensioner for a stretched chain since it was starting to rattle. I've had an issue with the turbo inlet after getting here, it blew off a couple of times (maybe that issued a stored code in the ECU, making it run a little rich to be safe?) but now that I've cleaned the hose off properly before tightening the hose clamp, I'm not having that issue anymore. The car just ticked over 131000 mi.

Anyways, I know this isn't a lot to go on, but if anyone has a suggestion as to how I can tackle this issue, I'd greatly appreciate it

Altitude. Don't know how high you were (no pun intended) in CO but Lambert field altitude at St. Louis is 605', greater air density. Has a hell of an effect on a golf ball too. That's something to look in to (not the golf balls). The MPG you are now reporting is about what most of us here at 1176' are getting.

Thanks for the reply! I think you might be onto something with having more dense air here. I plugged in values from the engineering toolbox (7000' in Colorado) into the fluid drag equation, and found out that I should be getting around 29.5 mpg if I'm ignoring all types of mechanical drag. I think I'll still try cleaning the MAF just to see if there's any potential for improvement there

You can also check the air filter, spark plugs, tire pressure to make sure they are all up to spec. Or just get a tune and forget about mileage muahaha, jk.

Glad to be of service. I used Lambert as an example. A little flying experience teaches that the average Cessna gets much better MPG at a higher altitude as well.

Not only does lower altitude increase drag, but the higher air density going into the engine means you run a lower throttle angle which also hurts efficiency (contrary to what CAI ads claim). Higher air density also means you make more power, but this also increases fuel economy. So if you tend to drive spiritedly or lightly, either way gets hit.

When's the last time the intake valves were decarbonized??


-Kevin