I have been getting ***-like mileage recently, 12-13 mpg. I haven't really changed my driving style or anything else for that matter.

I brought it into the dealership for this reason (risking labor if they didn't find anything).
So of course they found nothing, except that the battery failed the load test, meaning the alternator could be working overtime to charge it and killing mileage. They told me my battery was 26 months old and that in the hot weather down here this is just over the expected 24 month lifespan of the battery.

Sound plausible?

 

No, but the hot weather being bad for a battery is not new news. So getting a new one is not a bad idea. Also don't expect much help from the dealer in regards to MPG. Threads about the dealer fixing bad MPG are rare.

 

Sound plausible.

 

Well, I was working on a friend's RX-8 here in Phoenix last week and his battery was toast. When his fans would kick on, the load went straight to the generator and pulled his idle pretty hard. Putting in a different battery helped fix that, so I wouldn't be too quick to dismiss the idea that the added load might cost power/fuel.

 

Pieter, how many miles on the car? What was the mpg before? What flash level? Any loss in power? What grade gas - still use the same gas station? Using AC more often now? Is it strong or is so weak, it has to stay on all the time (lowering the mpg)?
Simply having a weak battery can maybe cost 1-2mpg, so if you lost more, try answer some of the above (i.e., I lost 4-5 mpg when dealer reflashed it last time... to save their weak cat, they dump unburned fuel into it to cool it down... what a great fix ! too bad I have to pay for it for the rest of my ownership... I have 15-16 mpg in mix driving)

 

It will definitely cost power/fuel.

It won't cost five mpg though, pieter3d. What sort of mpg have you obtained in the past?

 

If the bad battery had to do with the low MPG then a new alternator and/or starter won't be far behind. The entire starting and charging system works as a team.

CRH

 

Just thought I'd post an update. So I got a new battery and mileage seems like its back to normal.
Keep this in mind