Rear Hatch Spoiler Has MAJOR Detrimental Effect On MPG!

35 Yr Dsl Veteran

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Jul 19, 2019
Location
Ft. Pierce & Lake Placid, FL
TDI
2012 Touareg TDI Sport
I ordered vent visors for my 2012 TDI. Included was a nice spoiler/deflector for the skyroof, which I do not have. I mounted it on the top of rear hatch, to see what effect it has on rain, road spray, and dust on rear window.

Well, today going down a flat, level highway at 65 MPH actual (67 indicated), I was surprised my MPG was especially low, consistently only in the upper 20s. So I pulled over and ripped off said spoiler, and resumed trip at same speed, same flatness of road. Without spoiler, it read OVER 30 MPG, and consistently as I experienced before; 33-35 MPG!!! Plus, one stretch of the two-lane road, there was a line of slow vehicles, and backing off to 60 MPH, my MPG approached 40 MPG!
 

goodmonkey

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Anchorage, AK
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2014 Passat TDI, 2011 Touareg TDI
So are you 33-35 MPG ratings from the computer or from calculation of miles driven divided by gallons used? Just a few thousand of our miles on our '11 and we've averaged 22-25 (best 25) from fill up data.
 

35 Yr Dsl Veteran

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Joined
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Location
Ft. Pierce & Lake Placid, FL
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2012 Touareg TDI Sport
So are you 33-35 MPG ratings from the computer or from calculation of miles driven divided by gallons used? Just a few thousand of our miles on our '11 and we've averaged 22-25 (best 25) from fill up data.
Comparing apples & apples - several miles on flat road (elevation steady at 46 feet) at cruise @ stead 65 MPH with and w/o spoiler strategically observing instantaneous MPG display. Never went over 30 MPG w/spoiler, never went under 30 MPG w/o it. Quite obvious is made quite a difference.
 

goodmonkey

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Anchorage, AK
TDI
2014 Passat TDI, 2011 Touareg TDI
I'm thinking more about your 33-35 MPG comments elsewhere you are getting. I do get you could see the difference through instantaneous readings.
 

Fourdiesel

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May 19, 2003
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SW Wash. USA
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'04 Touareg V10 TDI
Agree w/ '35'. If the car computer showed "upper 20s" with the spoiler installed and later the same day, same road, same computer (duh!), same temp, same wind, etc the computer showed low "30s" then there really is a measurable difference attributable only to the spoiler removal. Now, if he had gotten behind a convoy of semis all going 50mph for 50 miles THAT wouldn't count! But that isn't what happened.
 

35 Yr Dsl Veteran

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Joined
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Location
Ft. Pierce & Lake Placid, FL
TDI
2012 Touareg TDI Sport
Agree w/ '35'. If the car computer showed "upper 20s" with the spoiler installed and later the same day, same road, same computer (duh!), same temp, same wind, etc the computer showed low "30s" then there really is a measurable difference attributable only to the spoiler removal. Now, if he had gotten behind a convoy of semis all going 50mph for 50 miles THAT wouldn't count! But that isn't what happened.
Wasn't just later that same day. Was immediately.
 

Fourdiesel

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SW Wash. USA
TDI
'04 Touareg V10 TDI
Sorry, "later the same day" is intended to be a somewhat vague term but with emphasis on the same day - just not specifying how MUCH later. 'Immediately' fits within the 'later in the same day' data set.
Even if it were a different day it wouldn't make any important difference as long as none of the engine parameters changed.
 

35 Yr Dsl Veteran

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Jul 19, 2019
Location
Ft. Pierce & Lake Placid, FL
TDI
2012 Touareg TDI Sport
And why's it on the spoiler instead of in front of the sunroof? lol
Was explained already; the vent visor kit included skyroof wind deflector along with four window shades. Vehicle does NOT have have said roof opening.

An experiment was conducted to observe effect (positive or negative) on aerodynamics/airflow on rain, road spray, and dust on rear window.

 
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