Long Distance MPG

[STS134]

Are we filling the EVAP system???!!! Attached a schematic picture, not PHEV.

https://www.moparmagazine.com/2018/07/too-much-in-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!

 

[twosout]

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.

 

[STS134]

Well I got new data points.

December 30, 2019: Going southbound, I topped off the tank to the brim with a gas can before leaving home. With a 100% full battery and a topped off tank, and with traffic moving slower than usual on I-5, I got as far as Glendale, CA (a distance of around 330 miles) at which point, there were around 30-35 miles left on the range meter.

January 4, 2019: Coming northbound, I put the vehicle into Charge mode and got the battery up to around 80%, and stopped in the Northridge neighborhood of Los Angeles, just off of I-405, where I topped off the tank to the brim. I got about 3.5-4 additional gallons into the tank, and drove for approximately 120 miles before the PHEV Watchdog showed the fuel level tick down from 99% to 98%. Fuel warning light came on when I was on CA-152, between I-5 and US-101, with 280 miles on the trip meter since I last refueled, and when I stopped in Gilroy for fuel, I had around 37 miles left on the range meter, 4 of which were from the battery. Eco Information screen was showing 22.9 mpg (although this included some driving on battery power and driving in slow LA traffic which means that for the I-5 section of my trip through the San Joaquin Valley, I was probably getting 20-22 mpg) and had I not topped off and started with an empty battery, I estimate that the fuel warning would have come on after approximately 180 miles (subtract approximately 85-90 miles for not topping off and 10 miles for not being able to use battery power). Which is, well, grotesquely inadequate, even for a PHEV. Of course, the tradeoff for higher gasoline range would be a shorter EV range, since the tank is physically sandwiched between the battery and the rear motor, which is why it's so darn small, and I'm not sure that's such a good tradeoff to make either.

 

[ThudnBlundr]

If you feel that badly about it, maybe you should trade it in for something you like rather than boring us by repeatedly telling us how much you disagree with the compromises the engineers chose in its design.

 

[Tai626]

My wife has the car 99% of time. Her commute is 4 miles each way. She doesn't need to gas station for long time (every 2 ~ 3 months) and just to top off which she usually do. If the PHEV has a bigger tank, it will weight more to hulling around.

Tai

 

[STS134]

My wife has the car 99% of time. Her commute is 4 miles each way. She doesn't need to gas station for long time (every 2 ~ 3 months) and just to top off which she usually do. If the PHEV has a bigger tank, it will weight more to hulling around.

Tai

You know you don't have to actually fill the tank all the way right? For example, planes only carry enough fuel to reach their destination, plus a small amount for reserve. But they're not going to install a 750 mile tank in a B738 that's usually used for short hops, since that would limit its utility for longer range flights. The operator is just expected to only fill the tank enough to get the plane to its destination.

 

[Tai626]

Tell that to my wife and I will get a smack...from her (ex-LV) bag. She considers 3/4 tank empty and 1/2 tank really gets to her nerves Call it an extreme case of range anxiety!

Now she is very happy with two full bars every morning. It is only time I am glad that our PHEV has a small tank.

Tai

 

[jaapv]

My wife has the car 99% of time. Her commute is 4 miles each way. She doesn't need to gas station for long time (every 2 ~ 3 months) and just to top off which she usually do. If the PHEV has a bigger tank, it will weight more to hulling around.

Tai

You know you don't have to actually fill the tank all the way right? For example, planes only carry enough fuel to reach their destination, plus a small amount for reserve. But they're not going to install a 750 mile tank in a B738 that's usually used for short hops, since that would limit its utility for longer range flights. The operator is just expected to only fill the tank enough to get the plane to its destination.

There is a difference between stopping in a petrol station to refuel and having to land on an airport which charges hefty landing and departure fees.
Having said that, I have been in quite a few light aircraft where the pilots had established fuelling points by keeping canisters of fuel in the Bush surrounding the dirt strips.

 

[twosout]

You could always carry a jerry can in the back (20l extra).

 

[ThudnBlundr]

I find it annoying enough that it starts flashing warnings when there's a third of a tank left. It's hard to ignore the warnings, and I've very seldom been able to put more than 40l into the car

 

[twosout]

I've gone until it refuses to provide a "miles remaining" but only put in 39litres. I fill 'til the pump stops, then continue to a whole number of litres, so not to the brim. Last time it was showing empty, I added 25litres and it took the gauge to 3/4.
I always add easy amounts to remember, to aid completion of my consumption records. So far 2421kW of electricity + 537litres of fuel have taken me 8725miles and there's still 25litres in the tank.

 

[Tai626]

For my gas only cars, I have been doing the same: only fill 10 gallons each gas stop. But with an add on intention: easy MPG. After each 10 gallon, I run the car until the reserve fuel light is on. At this point, the trip odometer should show the MPG x 10 (easy math) because it is when I reset the trip odometer to zero, find a gas station before the the car really run out of gas, and refuel only 10 gallons again. In my credicard, I can also track the actual gas price fluctuation $ per gallon, just divide by 10 (another easy math)

It is the extreme opposite of range anxiety I am taking unnecessary risk to really run out of gas and I have notice that I burn the reserve fuel light way too fast because it is NOT designed to be used this way. But I get the fuel mileage for every tank easily

Needless to say, it doesn’t work on PHEV if I plug in every night.

Tai

 

[Tai626]

Double post.

 

[Tai626]

I've gone until it refuses to provide a "miles remaining" but only put in 39litres. I fill 'til the pump stops, then continue to a whole number of litres, so not to the brim. Last time it was showing empty, I added 25litres and it took the gauge to 3/4.
I always add easy amounts to remember, to aid completion of my consumption records. So far 2421kW of electricity + 537litres of fuel have taken me 8725miles and there's still 25litres in the tank.

Just to play a little your numbers:

1MPGe is defined as 1 mile/33.7 kWh.

https://cars.usnews.com/cars-trucks/what-is-mpge

meaning 2421kWh = 71.8 US gallons of fuel (in terms of energy)

Real fuel burnt in US gallons = 537/3.6 = 149 US gallons.

The MPGe = 8725/(71.8+149) = 39.5 MPGe or 16.8km/l or 6l/100km.

And there are still 25 liters in the tank and probably 10kWh in the batt to spare

Pretty good for an utility vehicle!

Tai