Gas cap Effecting Fuel Milage?

[ComancheKid45]

Alright weird question.....could a bad/leaking gas cap cause fuel milage to drop?.....like by the fumes escaping from the tank?

[BLHTAZ]

On later model vehicles it could have some effect, but minimal as it is part of the evaporative system and holds vacuum. I don't believe it would have any effect on our trucks though.

[chicofuentes0224]

How about having an air leak at the sending unit? Do you think that would affect gas mileage?

[WahooSteeler]

It's not that the fumes are leaking it's that more air is getting in.

 

Taz, couldn't it be vapor lock and therefore the ECU is whacked out on fuel/air mixture? Kid45, I assume your truck is injected?

 

Before I ran a commercial truck fleet I ran a large car fleet, and we had some that were very sensitive to loose fuel caps, Volvo in particular. If it got vapor lock, check engine came on and they ran so crappy they couldn't get ouf their own way.

[BLHTAZ]

Yea...it's possible, but I don't think it will have any major effect. The newer vehicles will pop the check engine light if the gas cap leaks just a little bit on todays vehicles, but our trucks do not have that type of monitoring system.

[FxRacing282]

i do not see how air entering and vapros leaving will effect gas milage. seeing as on a full tank of gas you get about the same as empty. and the sending unit does not suck air up.