Is New Exhaust Hurting Gas Mileage?

[rllovett]

I recently had new pipes and mufflers installed on my (new to me) 94 Eldo (126k) and have noticed a drop in around-town mileage from around 17-18 to about 16...could it be the cold weather we've been having in the NE? The reason I suspect the new exhaust is cuz it was done with ribbed not smooth pipes (AT THE BENDS) and was left a little lower to the ground than the old, i.e., not a perfect installation...any thoughts/experience in this area would be greatly appreciated...Would an increase in back pressure lower the mpg? Would a lousy install make a significant difference?

[Dasher]

Not sure about the exhaust but cold weather certainly drops your mileage. I'd say you are lucky to be only losing 1+ mpg between warm weather and cold. You probably won't know if the exhaust is involved until it warms up.

[JasonA]

Yes, I think an increase in backpressure would affect the efficiency of your engine, but just the difference between the crimped/ribbed pipe vs. factory shouldn't be 2 mpg. The mufflers, if replaced, would make more of a difference I think. Also consider warmup time and such during colder weather when you're comparing fuel mileage. The colder weather itself shouldn't directly affect the mileage, but if you let your car warm up more in the morning, that'll certainly affect it.

[rjhat]

Did you put performance exhaust on? Generally speaking, perf. exhaust should increase your gas mileage as long as your foot doesn't get too happy with the new pipes. This is not true in all cases, but holds up in most. If you replaced your mufflers with an aftermarket brand that is more restrictive, then you may see a difference in mileage. Usually, engines run better with cold air. If you visit dragstrips, some racecar drivers will put bags of ice on their intake manifold to promote cooler air intake and will actually make a little more power. It is unlikely that cold weather is effecting your mileage, as your probably not running the AC compressor during the winter. If the mufflers are the problem, it stands to reason that you should have seen at least a small decrease in performance, especially if the engine is having to burn more fuel to go the same distance. If all else fails, i would just try a general tuneup for starters, making sure to change the air filter, which could rob you of gas mileage.