I was wondering if any else had a similar experience?



I have a HCH 05 CVT. Yesterday after filling up my second tank ever (I've owned the car since 08.31.05) I was getting exceptional readings off my instantaneous MPG o-meter. There is about a 1 mile stretch of road leading to my home that has a very slight incline (basically flat, but definitely not a decline!). The meter was maxed out the entire time after I finished accelerating from a stop light up until I braked to enter my development.



My average for the 2 MI trip back from the gas station was 80+ MPG. Normally I'm happy to get over 50MPG, and I'm just beginning to get a feel for the 'sweet spot' in gas pedal depression. However, the fact that I was able to go 120+ MPG, while staying at the same speed, if not accelerating a little bit up a slight incline for an entire mile seems to me a bit strange.



Has anyone else experienced this? Does anyone have any plausible explanations? Perhaps my gauge is broken?

 

If you overfill at the pump and get gas into the evaporative emission canister then you can get funky FE readings, this is because the FE gauge is based on the amount of gas added via the fuel injectors. Gas or fumes that come from the evaporative emission canister are not counted towards the total fuel used, and increase your displayed FE.

If your state does not mandate the use of vapor recovery systems on the fuel pump, then the evaporative emission canister will absorb a small amount of gas fumes when you fill up, these fumes are then used by the engine and will artificially inflate your FE display temporally. This usually doesn’t last very long, but dumping liquid gas into canister will have a significantly bigger impact and will last longer too.

States that do use an advanced vapor recovery system (such as CARB compliant states) remove the vapor from the gas tank and do not have nearly the FE impact since the vapor recovery canister inside the car is used very very little.

Be careful not to overfill (don't top up), it can damage your car and may not be covered under warranty. The people who can get significantly more gas in their car then the gas tank size are actually filling their evaporative emission canister with gas, and their displayed FE can be wildly different then the hand calculated number. This might be convenient because they don’t need to fill up as frequently, but it does have significant risks associated with it as well.

~Droid

 

This could also explain those who talk about getting better gas mileage on a full tank. It wouldn't affect gas mileage figured by hand, of course (miles driven divided by the gallons that came out of the pump, probably the only reliable way to figure mpg).

 

droid, i'm with you on this one. i've never topped off my hch and don't intend to anytime in the future for the reasons you gave.

i know people top off all the time with just a couple clicks, and that's fine, shouldn't matter too much. but the drivers that fill their tank until it literally almost overflows out of the filling tube are the ones i'm mainly concerned about. i don't think the tank was made to hold that many gallons (13.2 gallons intended, filling it up to 15 or 16 gallons) nor was the evaporative emission canister designed to handle so much overflow. of course, it's all up to the driver.

 

Uh oh, now I am REALLY worried!

Droidicus, how do you fill up your tank, might I ask?

I don't top the gas off. Well, if by 'topping off' you mean pumping until the pump stops, then yes, I was topping it off. But if you mean going 'a couple [extra] clicks', I didn't do that, nor have I ever in my life for any car.

So, should we be 'guessing' how much gas to put into the tank based on the number of 'bars' left on the gas gauge?

RRGY2k...If 'guessing' is how we're SUPPOSED to fill up our tanks (say if I have 3 bars left on the gauge and I pump 10 gallons to avoid 'topping off the tank' when in actually 11 gallons of gas were used since the last fillup), we would grossly over estimate our 'by hand' MPG (which, by the way, is how I happen to enter my MPG into the GH database). For example, if I drove 550 miles on this tank, and I guessed I needed 10 gallons to avoid 'topping off the tank', I would come up with 55 MPG by hand. However, if the number of gallons used during said tank were actually 11 gallons, my actual MPG for said tank would be 50, and my calculated MPG would be off by some 10%! So, I'll assume the 'guessing' technique of filling up your tanks is not what people do.

So this issue is not bring me grave concern! Is there something wrong with my gas tank? Based on what I've read, you all seem to be in agreement that I am 'topping off' my tank. However, all I do is merely fill the tank till the pump stops pumping, I don't add any extra 'clicks'. So, the only logical conclusion is that there is something wrong with my tank...it causes the pump to pump further than it is supposed to and this will 'damage [my] car and may not be covered under warranty', according to Droidicus. I'm sure the insurance adjuster wouldn't take my word that I am not 'topping off the tank'.

Should I take my car back to the dealership to have this matter looked into? Please help! Extremely worried now!!!

 

Woah, settle down...

The "Proper" way to fill up the tank is to wait until the gas pump clicks off by itself, then just put the gas cap back on ;-) You might hear people around here refer to that as filling up to "the first click".

Sometimes when filling the tank up to the first click a small amount of liquid gas will get into the vent for the evaporative emission canister, a small amount isn't something to be worried about. This will artificially inflate the FE for a short period of time after filling up, I usually see it for 10 miles or so. The thing that could be damaging is to keep putting in more and more gas after the first click (or 3rd, 5th, 20th, etc), some people actually put gas in until it is about to spill out of the filler neck... that can damage the car as the gas system was not designed to operate that way...

If I were you I wouldn't worry to much if I were you unless you see the FE pegged at 120 mpg at times you wouldn’t expect and for extended periods of time (like over multiple days), or if the check engine light turns on as that could indicate if there is a problem with your car's emission control system.

Hope that helps,
~Droid

 

As Droid said, you can put your mind at rest. Your car is fine. Just fill the car until the pump shuts off. Overfilling is when you go past that point.

On your 120 MPG adventure, I would say that as capabile as our hybrids are, they cannot overcome the laws of physics. A car cannot move uphill without energy being applied. In the 45K miles I've driven my Civic, I've learned that it takes a reasonable grade downhill to coast at 120 on the display and maintain speed. You still need to overcome wind resistance and friction from the tires. I believe what you experienced is from the fact you just filled the tank.

There are many times where you'll get brief runs or even a tank where the mileage is very high or low. I've posted before on the dozens of variables at play that will affect your mileage (wind, rain, hot, cold.....). Don't get too worried about what happens over 1 mile. I suppose if you had a 40 MPH tail wind you might be able to go uphill on 120. :-) In general, what your car does over a month or a season is a better measure.

 

environmental wakko

Sounds like it may be a good candidate for FAS?

 

sorry environmental wakko for making u panic

Topping off is when you add extra gas after the gas pump stops pumping. What you did was fine, and just an eccentricity. No worries

 

on another note, i was amazed today at getting 50.3 mpg over an 11 mile trip that involved a 3.3 mile hill I pulled up @ 2500-3000 rpm with 66-80% assist. the whine i get from the electric motor + engine at 3000 rpm is great. I love how the cvt selects just the right rpm for climbing hills. (hch cvt hits peak torque at 3000 rpm. while manual hchs hit peak torque at 1500 rpm)

the rest of the trip was just traveling on level roads in the city, with no FAS. usually i make this trip and get around 40-42 mpg, but today my car had been warmed up after driving 16 miles back from another place. its a wonder what having a warmed up engine can do for your mpg.