MPG loss from Roof Vents and Covers??

[LMTLMT]

I thought maybe some of you who track MPG can enlighten on this subject.  I try to search but didn't find any that relates to MPG and Roof Vents.

I plan on installing 2 non-fan roof vents.  I also have two roof covers as well (still thinking about if I'll put both covers on or just one).  

Question 1, any MPG loss with roof vents?  If yes, how much?  (and I have two if that makes any difference.  Most likely it'll be installed in the center, one front, one back)

Question 2, any MPG loss with roof covers?  If yes, how much?

Thanks much.

 

[poncho62]

Just a guess, but I would say no difference. I would think that changing your air pressure in your tires (rolling resistance) would make more of a difference

 

[MrNoodly]

I would think that changing your air pressure in your tires (rolling resistance) would make more of a difference

The weight (or lack thereof) of the stuff you haul in the van would have a greater effect.

 

[closeanuf]

You might take off your outside rearview mirrors; they create a lot of resistance.

 

[Optimistic Paranoid]

To my mind, the increased comfort and livability that roof vents and covers (for the ability to have the vents open in inclement weather) FAR outweigh whatever gas mileage penalty they may incur.

 

[flying kurbmaster]

they will only cause mpg losses over 50mph It would be minimal. if you install an air dam under your front bumper you will likely gain back those losses and then some. At speeds lower then 50mph weight is the issue not aerodynamics so if your drive around the city you will not loose any mpg if you drive on the highways you will loose some, two will be worse then one, unless they are placed very close together. if you built a small sloping wing on the back side at 12 to 15 degrees you would minimize the losses some more. A better place to ask this question is at ecomodders.com I am sure someone there has tried it with all the numbers.

 

[Spaceman Spiff]

. . .

Question 1, any MPG loss with roof vents?  If yes, how much?  (and I have two if that makes any difference.  Most likely it'll be installed in the center, one front, one back)

Question 2, any MPG loss with roof covers?  If yes, how much?

Depends . . . on the shape of the front of your vehicle, where they are placed, how high they stick up.

I have a pop-up camper on a pickup.  Using the poor man's wind tunnel (bugs, of which we get a lot of in the summer) I get lots on the front  of the truck and camper.  I get none on the front face of my solar panels on the roof 1 ft. back from the front, I get none on my MaxxFan cover 2/3 of the way back, I get none on a 4" high antenna mount that sits next to the fan cover.

IMO, one would have to run a very careful experiment to measure the MPG loss of a standard RV roof vent back from the leading face of a vehicle..  I don't know about the covers as they stick up ~ 8" above the roof.

 -- Spiff

 

[Gary68]

your basic roof vent that sticks up 1'1/2' ,nothing,the air will flow above it

those 8" covers, a touch

 

[LMTLMT]

Thanks everyone who chimed in. Appreciate the comments. I'll be using the van for road trips only and stealth camp at Hospitals, Truck Stops and etc. Most of the time I'm driving on the interstate and steady @65mph . My major expenses are fuel and food. If the roof vents will loose MPG to 3 or more, I might think about not doing it.

The van currently gets 20.282 MPG doing steady 65mph on the interstate.

The need for roof vents have been debated and everyone has their ways. I think I'll be more comfortable with two roof vents so the van won't be all musty and condensation build up. And the Covers will help a lot when sleeping during rain. I know I can't have it all but one can wish right? lol

 

[flying kurbmaster]

you will never loose 3mpg you might loose the .282