Effect of fuel cap on fuel consumption

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Feb 26, 2009 | 08:30 PM

Jim314

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Effect of fuel cap on fuel consumption

A relative of mine recently bought an XF Supercharged and remarked to me that he was getting less than 15 mpg in town. Then he noticed some instructions (maybe on the gas tank door, I didn't get this detail) that the fuel cap is supposed to be tightened at least three clicks, and he had only been tightening one click. He changed to three clicks and immediately got 21 mpg on his trip to work.

What is the explanation for requiring three clicks, and could this make this much difference in mpg without the message center alerting the operator? On my Volvo a failure to properly seat the gas cap gives a warning light and maybe a message.

Feb 26, 2009 | 09:06 PM

Brutal

Joined: Sep 2008

Posts: 7,255

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From: Damon /Houston, Texas

each click = 3mpg over 13 mpg, if you go 5 clicks youll get 28!........

\
coincidence. 3 clicks to make sure its close

Feb 27, 2009 | 09:39 PM

jagular

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Joined: Nov 2008

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From: Calgary Alberta Canada

This is to ensure that the cap is on tight. If it isn't then the tiny air leaks can throw a code which triggers the CEL (or MIL if you are British). In fact, if the cap is sealed then the CEL will not go on. Three clicks ensures that the seal is tight is all.

Feb 28, 2009 | 02:12 PM

Jim314

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Thanks for the replies. Probably the higher mpg achieved after the cap being tightened three clicks was due to the remainder of that trip being started with a fully warmed-up engine and the trip being mostly freeway. I'm guessing that the low mpg values obtained before that were due to a large proportion of very short trips.