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Gas Consumption SLK230 top up/down results

3K views 9 replies 7 participants last post by  Tummy 
#1 ·
Ok, as promised in an earlier thread, here's the final results of my 'research' regarding gas consumption while driving with top up and top down.

In order to keep things as consistent as possible I use the same gas station [QuikTrip, 93 octane] for both tanks of the test. I also ensured the tire pressure was the same for both tanks [30 front / 33 rear]. I didn't run the tank all the way empty on either test, but I tried to refill as close as possible, so for the top up test I drove 301 miles and for the top down I drove 259 miles. I don't have any modifications to the engine/air intake/etc. It's all stock.

On both tanks, I drove maximum of 70 mph, using cruise control as much as possible to maintain the same speed.

With the top closed up I used 11.371 gallons for 301.0 miles. That equates to 26.471 miles per gallon.

With the top down I used 9.677 gallons for 259.0 miles, which equates to 26.764 miles per gallon. Slightly better! :)

The week I drove with the top down was slightly cooler than the week with the top up, so I don't know how much that affects gas mileage, but all in all it appears as though I get almost exactly the same gas mileage regardless of whether the top is up or down.
 
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#2 ·
Interesting comparison, I'll have to try that with mine. I'm actually glad to see the price of oil has actually gone down the last couple of days, we'll see how long that lasts... BTW, I can't remember if I told you or not, my wife and I will be SATX the week of 18 August, any chance you'll be around?
 
#6 ·
Interesting comparison, I'll have to try that with mine. I'm actually glad to see the price of oil has actually gone down the last couple of days, we'll see how long that lasts... BTW, I can't remember if I told you or not, my wife and I will be SATX the week of 18 August, any chance you'll be around?
How long will you be there? I won't be off work until that Wednesday & Thursday. Maybe we could meet halfway, depending on your schedule? I think Kevin [DesignoSLK] is also going to be in the area around the same time if I remember correctly.
 
#3 ·
That's interesting. On my previous car, an Audi TT roadster, we got around 25% better MPG with the top up. I haven't done a formal test on my current car, but I think it does better with the top up. We're going on a 2000 mile roadtrip in August and I'll try it then.
 
#8 ·
I'll be around the 18th of Aug for sure, as I live in SA :biglaugh:.

For the top up/top down mpg comparison, I think the top down decreasing mpg really only comes into play at highway speeds over 65mph so if you did any city driving at all, even if it was just 20% of the total miles driven, it could skew your numbers down to make top up/top down appear more even. At any rate, the SLK has a relatively low profile and small footprint, especially the kompressor version, so top down driving would only alter wind resistance slightly. The mpg should be pretty darn close, within 1-2mpg tops I would say, even for 100% highway driving. Wind screen could come into play as well (having vs not having one that is).

The only way to get a "truely" accurate comparison would be to pick the same 150-200 mile stretch of highway, going the same direction, approximately the same temp/heat index (affects road temp therefore tire "stickyness"/traction which *could* in theory affect mpg), with the same amount of wind within a mph or 2 coming from the same direction. Real world tests are very difficult to make very "scientifically accurate". Personally, I'll just take your results and run with them as my reason to drive with the top down!
 
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