Mitsubishi Outlander PHEV Forum

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 Post subject: Re: Long Distance MPG
PostPosted: Sun Feb 03, 2019 6:01 pm 
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Joined: Wed Jul 11, 2018 4:35 pm
Posts: 170
Location: Saratoga, CA
Tai626 wrote:
Are we filling the EVAP system???!!! Attached a schematic picture, not PHEV.

https://www.moparmagazine.com/2018/07/t ... -the-tank/

Tai

So I looked up exactly how the EVAP system works, and the short answer is, NO, it's impossible to fill the EVAP system lines and canisters with fuel, unless there is something wrong with the system itself.

For filling the tank, there are TWO lines that go from the filler cap to the tank: the fuel line, and the return air line. The fuel inlet has a sort of "check value" on the end of it that prevents fuel from flowing backwards, and the return air line is a tube that extends downward into the tank. When fuel in the tank rises above a certain level, air can no longer escape through the return air line; all remaining air in the tank is now trapped, and cannot leave, as the end of the return air line extends so far down, the tip is immersed in fuel instead of air. This is what causes the pump to click off when the Venturi pipe starts to suck up gas instead of air. Now, what happens from this point on is that you actually start filling the two lines (the fuel filler line and the return air line) with fuel. The air that was trapped at the top of the tank however, remains trapped there. As you pump fuel into the fuel inlet line, fuel will also start to move back up the return air line to the nozzle until the level of both is equal. This explains why the speed at which the fuel drains gets slower and slower as you you keep pumping; initially, the filler line is full and the air line is empty, and fuel will quickly drain into the tank and push fuel back up into the return air line, but as more and more fuel fills the return air line, the difference in pressure gets lower and lower and it drains slower and slower.

Will this harm the EVAP system? No. First of all, there is ALWAYS air trapped at the top of the tank, because that return air line extends downward into the tank and the system cannot remove all of the air from the tank. Second, the EVAP system contains a liquid-vapor separator between the tank and the EVAP lines. This would actually be necessary even if you didn't top off the tank at all, because fuel sloshes around when you drive. Furthermore, the EVAP system does not operate unless the tank is between 15%-85% full; at other times, the EVAP solenoids remain shut at all times. The only way you could possibly get gasoline into the EVAP canister is if the EVAP solenoids malfunction and the engine draws a vacuum with the tank full AND the liquid-vapor separator also fails (or wasn't designed to handle such a strong vacuum).

So...the capacity of that filler line and the return air line is apparently around 10L or so!


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 Post subject: Re: Long Distance MPG
PostPosted: Mon Feb 04, 2019 4:41 am 
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Joined: Sat Oct 06, 2018 3:24 pm
Posts: 89
Location: West Midlands, UK.
STS134 wrote:
Tai626 wrote:
So...the capacity of that filler line and the return air line is apparently around 10L or so!

I agree with everything except the conclusion in your last sentence.
10 litres is a large capacity for a bit of (even chunky) pipework.
I think it more likely that most of them were still in the (bottom of the) tank before refilling.


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