Awful Mileage

[HokieZHP]

So recently I've noticed that my gas mileage is going down. For instance, I drove back to school today and my average was around 23mpg at 75mph... Normally it's at least 28mpg. I've noticed it around town as well. But on the highway the instantaneous mpg gauge in the cluster rides much lower than normal at constant speed. It has a K&N drop in filter with not even 5k on it. Any ideas guys as to why my mileage sucks all the sudden?

[danewilson77]

AFE helped my gas mileage a lot.

Could be tires, plugs, I dunno. You still have rack on your car? I would put stock paper back in. That K&N is oiled....correct?

[JohnnyGraphic]

I'm just throwing out ideas-but if this drop in mileage happened after the new K&N filter, it could be that oil from the filter element got on the mass air flow sensor and is causing some erroneous readings??? If it's a dry filter, then I would check the usual culprits-air pressure, fuel filter, spark plugs etc to see if they are within spec and or if they have been recently serviced/changed. Gas type would also be an issue? Is your roof rack recent?

That's about all I can think of for the moment.

Hope you find out. In any case, 23 is about average for me-combined city/highway and I do mostly highway. 28 at 75mph would be great for me.

Johnny

P.S. Maybe it needs a good wash and wax? LOL!

[HokieZHP]

I'm just throwing out ideas-but if this drop in mileage happened after the new K&N filter, it could be that oil from the filter element got on the mass air flow sensor and is causing some erroneous readings??? If it's a dry filter, then I would check the usual culprits-air pressure, fuel filter, spark plugs etc to see if they are within spec and or if they have been recently serviced/changed. Gas type would also be an issue? Is your roof rack recent?

That's about all I can think of for the moment.

Hope you find out. In any case, 23 is about average for me-combined city/highway and I do mostly highway. 28 at 75mph would be great for me.

Johnny

P.S. Maybe it needs a good wash and wax? LOL!

I just washed and waxed before I left haha

It's oiled but never had issues when I had it in there before, no reason why there should be now. Will probably go back to stock paper this week. Which size do we use again?

Plugs were replaced ~8k ago. No weird gas. Roof rack normally is only a 2mpg or so hit at the MOST.

I'll replace the filter and see how that goes.

[az3579]

^^ Or you could just clean your MAF and try your mileage then. Don't necessary have to replace the air filter... perhaps it's just finally gotten to the point where the readings are being affected from the usual gunk that gets in there.

[HokieZHP]

^^ Or you could just clean your MAF and try your mileage then. Don't necessary have to replace the air filter... perhaps it's just finally gotten to the point where the readings are being affected from the usual gunk that gets in there.

I just replaced the MAF like 2k miles ago so there shouldn't an issue there either.

Then again, the drop could just be from my racks and weight in the car...I don't think it would cause that kind of drop though.

[brettbimmer]

Hmmm...could it be in part because you are driving into a headwind? Or uphill, esp. on the highway? Sounds like two minor points, but given the wind this winter, I have seen it affect my mileage a bit.

[az3579]

I just replaced the MAF like 2k miles ago so there shouldn't an issue there either.

Then again, the drop could just be from my racks and weight in the car...I don't think it would cause that kind of drop though.

Those two things absolutely will affect your mileage, potentially to a great degree. The rack increases drag, and the weight makes the car work that much harder to 1) maintain speed and 2) carry its own weight. 23mpg is what I would expect from someone averaging 75-80mph if they drive in an area with frequent inclines. That's one reason I keep it at 65-70; the mileage is vastly better when you take hills into consideration. How much weight are we talking here? It could be the weight that's dragging you down; do you have extra junk in your trunk or something?

Also, do you drive a lot on the highway when the engine is cold? My mileage is easily 10mpg less when I get on the highway in the morning going to work as opposed to me taking the same route with a warmed up engine. The engine runs rich when cold.

I'm feeling that my mileage has overall been worse since it got cold. During the summer I could easily get 31-32mpg on the highway but this winter the highest I've been able to hit average was 30.x mpg. This has been the case with my previous car as well, for some weird reason. Of course, the higher the speed, the more pronounced the effect.



If you've been stressed recently, or started listening to music (or a different type of music), then these could affect your driving style and you may not realize it. Is anything different about the car, you, or your environment than when you were getting about 28mpg?

[HokieZHP]

Maybe 40-50lbs. Ski racks on top with 1 set of skis.

It just seemed weird since I normally get high 20s at that speed on that route.

New starter motor on the car is the only difference recently.


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[M0nk3y]

Wash and Wax doesn't do anything...except for the few centimeters on the hood of the car. Gotta love fluid mechanics

I'm going on the basis of just bad driving weather. I've had good days where I've averaged 28 mpg on my S54 just tailing cars and respectable distances and as low as 24 mpg just driving on my own.