Hi guys,
I've posting this thread because I've been having a concern about my AVG MPG that I don't know if I should be concerned about it or not, that's why I want to share to see if the same is happening to some of you.
Twice a week I drive to a clinic for working reasons which it is about 60 miles away my job's headquarter.
My Avg MPG meter shows between 30.2 and 30.9 (usually 30.5 mpg) when it doesn't rain, I always check it when I arrive. The last 2 times that it rained (the last one was today) I've noticed a significant drop of avg MPG.
The first time I thought that maybe I drove differently from usual by pushing a little more than usual, but today I drove just the same as when it doesn't rain to see if the result was the same.
When I arrived, I've checked it and it said 24.3mpg just like the previous time (the previous time was actually 24.5mpg).
Now, everything was the same as when I drive with no rain, such as outside temperature, traffic condition and the way I drive.
Is it something I should be concerned about? I mean, droppign of about 6 MPG just because of the rain? Does it sound right or it may be the beginning of some kind of problem?
I have the AEM filter that came with the AutoWerks kit, it is not a CAI.
Thank you guys for reading this thread.
Christian

 

Does it happen to some you guys? Or did you ever heard about it? Any idea of why it happens?

 

Could be many things, notice a difference in performance?

 

No, not at all. The only difference I can think of, other than the fact that it was raining, is that maybe there was a difference of outside humidity. But even if it the reason ,damn!! 6mpg?

 

I hope that either whyyoumadson or someone at ZZP chimes in. They may know of something about thid

 

did u ever check your intake filter to see if it is wet or damp?

 

Yes I did, the air filter is just fine

 

something has to be getting wet/damp obviosly that the rain is making u lose mpgs. i would just check under the hood to see if any splashups r leaking in or water is getting in somehow

 

With rain comes bad air, bad aerodynamics, more rolling resistance, etc. Not to mention, wind direction will kill or add, depending on direction, a few mpg on top of that also, which you would never notice unless you stopped and determined the wind direction in relation to your travels. Most likely, it was raining and you were going into the wind, and theres nothing wrong with your car.

 

No, it wasn't windy at all. Damn it is really hard to believe that bad air and aerodynamics would bring me down so much! Holy damn!! Does your car do the same? Did you ever check the difference of your mpg between dry and wet weather? I'm so curios to get some input from some other guys.

 

I have 106k on my 07 and constantly watch mpg and what affects it. Not a turbo, but it doesnt matter when discussing aerodynamics and rolling resistance. Aero is huge to get mpg. It doesnt have to be "windy", a light 5-10mph breeze you would hardly notice will knock a mpg or two off when going into it at highway speeds compared to going WITH the same wind.

 

If that's the only time you noticed a drop in MPG then It's the difference in temp/conditions that affected MPG, It's the only thing that makes sense generally in the rain you may not push her hard but the colder weather/atmosphere makes the motor work harder to get the car down the road, The poster above pretty much sums it up! Rolling resistance and dont forget in the rain you may be using defrost and wipers which is a drain on the motor!

 

At this point the only thing I can think is the resistance, because this decrease happened both times when the outside temperature was the same as when I get 30.5mpg with no rain.

 

The temperature may be the same, but the air density is what makes a difference in engine performance. It is a function of the temperature, air pressure, and vapor pressure.

 

Up to the point to drop by 6mpg? Well, that sucks but if it is true it makes me feel better because at least there is nothing wrong with my engine, that's what I was fearing

 

Your drop in mpg is a combination of things I've listed, not just one.

 

No no, I think you misunderstood my original post. I said that everything was the same as when I drove that car as I usually drive it when it doesn't rain: I said that my driving style, the traffic and the outside temperature was the same as when I drive it when it doesn't rain. The only difference was the rain. I never wrote that something was different

 

And still, I see the possible reasons you gave me, but Damn! Dropping 6mpg over a 50miles route? It seems really weird

 

I hope there is nothing I should worry about

 

Do you reset the mileage in the dic every trip?

 

Usually I reset it every fill up to see how I do on a full tank, but when I have to drive all the way there I reset it as well. I reset it right before I pull out of my drive way and I check it when I arrive to destination.

 

I normally get 24.5mpg back and forth to work but its been raining a TON and i'm down to 21.5... I've just figured it was due to added rolling resistance

 

Mine almost him 31mpg on highway, and 26-28 in traffic

 

Road surface conditions have an effect upon fuel efficiency, and this includes driving in rain. Although I'm not sure of the science behind it, I suspect that you are correct when you mentioned the resistance created by water on the road.

Sarah
GM Customer Service

 

You actually could be getting worse mpg due to rain. There is more rolling resistance on very wet roads due to the density of the water the car has to displace/move to get traction, plus you'll spin easier, so the engine has to work harder, resulting in worse mpg.