What's your least efficient mod?
 

I'm betting there are a few of us here that have done MPG-unfriendly mods. Maybe it's a heavy sound system, a lead foot, heavier wheels/tires, or neglecting maintenance.

What have you done? How bad did it hurt your mileage? Were you able to get your mileage back, or did you care?

I'm running sticky summer tires that are heavier and wider than stock. I went from an easy 43/44 MPG to a difficult 40. She looks really good.....for a commuter.

I started with the heaviest and least aerodynamic 1991 Civic body style. Does that count? :)

Electric water pump.
Its expensive, I don't think it helped MPGs any, caused some cooling system problems and it will make a alt delete more difficult due to the added electrical load.

Honestly? Getting new spark plugs. While I'm still in the 40s for mpg, it's dangerous knowing I now have some leeway in applying the go-pedal :D

Hard to say how much it's actually costing me since I'm in the unusual position of using this as my only family car. I'd say I'm still doing pretty well since a year ago maintaining over 40 using the car as the family car would have been laughable.

Swapping my '88 Civic wagon that died for a '98 Grand Cherokee 5.9 Limited. Went from 40ish MPG to about 11. I don't know if that counts as a mod, but I still regret it, even years later ha ha :snail:

I was the opposite of that with my old Mercedes to my Honda, so I could imagine how you feel. :eek:

I got a block heater and notice 0 effect on mpg. Next to that would of been doubling my starter battery capacity from 35 to 70 amps. Using heel fuel additive didnt help any. Going for cheaper gas actually lowered mpg.

Trading my 96 Civic for the Fit. Overall it's worth it, but I lost some mpg. Best tank in the Civic was 90 mpg, in the Fit is only 73, average down from 70 to 60.

But I gained:
New(er) car reliability
MUCH better cargo capability
Tighter driving dynamics
Working AC (that I don't use :p)

The mod that drives me crazy but I need it for my turbo compound system
(for racing) is my Tilton 40-527 external oil pump. It doesn't help at all with FE and takes away FE from the extra load on the alternator. So I decided to add a secondary deep cell battery to run it most of the time and charge this battery at home and work. I pulled around 200lbs of weight off the car so the extra weight from the deep cell won't be to bad.

Least efficient mod: Taking my truck on road trips instead of the GF's Cruze...

Personally, I'm fine either way. But she says my truck is more comfortable, has better leg room, and she can bring her many "necessary" bags... If we took the Cruze she'd have to pack sensibly... and we just can't have that now :rolleyes:

I buy the gas, she pays for the hotel, food and she carries her many bags herself!

As for the truck itself, I'd say the studded winter tires suck a good 1.5-2 mpg... stupid cold for 5 months of the year doesn't help either...