Hyundai Forums banner
1 - 16 of 16 Posts

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #1 ·
Fueled up today, a week shy of two months since the last and dumping the info into Fuelly turned up an average of 23.8 mpg. Down 8.4 mpg (!) from the last tankful. I'm used to this car's average doing a rollercoaster even though I don't drive much and 99% is city over the same roads. Might have had a little heavier foot but dang that's annoying.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #3 ·
Any other symptoms? Loss of power; hard to start; anything else. Or is it just the loss of MPG.
I noticed a little ticking, vacuum sound when getting on the throttle around 1,500rpm but only then, could be normal and it's just popped up so it's not likely a culprit.
 

·
Registered
Joined
·
4,656 Posts
Not saying this has to do with cars but on aviation, we don’t like to let helicopters or airplanes sit long with fueling not being topped. In theory due to condensation in tanks. Huey’s we topped off as soon as returning from last sortie.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #5 ·
Not saying this has to do with cars but on aviation, we don’t like to let helicopters or airplanes sit long with fueling not being topped. In theory due to condensation in tanks. Huey’s we topped off as soon as returning from last sortie.
I should probably throw some fuel stabilizer in there. I just don't drive much. Not much I can change about that.
 

·
Registered
Joined
·
1,443 Posts
I should probably throw some fuel stabilizer in there. I just don't drive much. Not much I can change about that.
Not sure if you are using a fuel cleaner like Techron, but short tripping is not good for the engine carbon wise and may contribute to less than stellar performance.
 

·
Registered
Joined
·
259 Posts
Maybe a tank of less than great gasoline could account for the sudden decline?
There are stations where I will only pay cash for gas, because of the dilapidated look of the pumps. How would I know if there were a credit card skimmer installed on a pump that is in rough looking condition? The pump could be falling apart simply from age and neglect, or else the looseness of the card swipe/ keypad inserts might mean that it has been tampered with. There are stations where I won't buy gas from at all because I don't want to risk being carjacked. And there are stations I won't buy gas from because if anyplace has leaking tanks or is deliberately watering down their gas, it's probably those places. Of course it's impossible with any of these areas of concern (bodily harm, financial harm, mechanical harm) to rule out being misled by appearances, but appearances and generalizations are all we have to go on sometimes.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #8 ·
Not sure if you are using a fuel cleaner like Techron, but short tripping is not good for the engine carbon wise and may contribute to less than stellar performance.
Maybe a tank of less than great gasoline could account for the sudden decline?
No cleaners used just top Tier Fuel, first few years Shell last couple (because of a grocery store rewards change) years have been Mobil. Both stations are less than 10 years old, the Mobil probably 5 or 6. Since I bought the car in '12 it has never not gotten Top Tier fuel (except for the first tank the dealer threw in, I tried to tell him not to put junk gas in it but they did) and of all the 73 fill-ups less than 10 have been at places other than the two that I normally go to less than 4.5 miles from here.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #9 · (Edited)
Yo-Yo'd back up 30.1mpg on this next fuel up. Someone designing rollercoasters could use my Fuelly graph for ideas. Added a bottle of Techron and filled with mid-grade to try and clear up some mild valve clatter.
 

·
Registered
Joined
·
95 Posts
Do you always use the same gas station? Just curious. I'm able to do that with my work, and in fact I almost always even use the same pump. I know others are not so lucky. Different stations may have pumps that shut off a bit sooner than others due to different equipment. If a pump at one place shut off early you wouldn't know and think it was full. The next time you fill up it will take more gas and this will throw off your mileage numbers from tank to tank. Of course this is just a guess...
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #11 ·
Do you always use the same gas station? Just curious. I'm able to do that with my work, and in fact I almost always even use the same pump. I know others are not so lucky. Different stations may have pumps that shut off a bit sooner than others due to different equipment. If a pump at one place shut off early you wouldn't know and think it was full. The next time you fill up it will take more gas and this will throw off your mileage numbers from tank to tank. Of course this is just a guess...
I've used the same Shell or Mobil station for my gas except once or twice when I was far from home and too low on gas to get to the home area. As for the pump, full is full. The receipt records the gallons to three decimal places and the pumps get inspected. I also use Fuelly to track my mileage so I know the math is right.
 

·
Registered
Joined
·
13,373 Posts
Yo-Yo'd back up 30.1mpg on this next fuel up. Someone designing rollercoasters could use my Fuelly graph for ideas. Added a bottle of Techron and filled with mid-grade to try and clear up some mild valve clatter.

I gave mine a taste of Techron, and some more seasonable weather has brought it around to 33MPG.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #13 ·
I gave mine a taste of Techron, and some more seasonable weather has brought it around to 33MPG.
I threw in a bottle of Techron and used mid-grade on the fill up before my drive to Kissimmee (150 miles a lot above 70mph). Will see what I get on this tank in a week or two. I'm used to the yo-yoing but that mega dive was disturbing.
 

·
Registered
Joined
·
95 Posts
I've used the same Shell or Mobil station for my gas except once or twice when I was far from home and too low on gas to get to the home area. As for the pump, full is full. The receipt records the gallons to three decimal places and the pumps get inspected. I also use Fuelly to track my mileage so I know the math is right.
I trust your math and I don't doubt that the pump is accurate in terms of you getting the amount of gas it says it pumped. Neither of these is what I was trying to explain.

Here is an explanation of how the pump know when to shut off:

https://auto.howstuffworks.com/gas-pump5.htm

".......As anyone who's ever operated a gas pump knows, the pump will switch off automatically. But how does the pump know when to stop pumping?
As the gas level in the tank rises, the distance between the dispenser nozzle and the fuel grows smaller. A small pipe called a venturi runs alongside the gas nozzle. When the end of the venturi pipe becomes submerged in the rising gas, it chokes off the air pressure that holds the nozzle handle open and shuts down the flow of gas. Unfortunately, this shutdown can sometimes happen before the tank is full as the rapidly flowing gas backs up on its way into the tank. This can cause the gas handle to spring open before pumping is complete, leaving the annoyed customer to squeeze the handle again and risk the possibility of overflow. "


The bold is by me, and is what I'm trying to explain.

No matter when the pump shuts off, the amount you get is what you pay for. Yes, the pumps are calibrated and inspected, but you always assume that the tank is full and shuts off the same when you fill it up. That may not be the case. It could have shut off a bit early, maybe 1/2 gallon or so early, maybe more. I'm just guessing here. The point is that it may not be full.

The next time you fill up, maybe it does fill up all the way, so what the pump will show is the amount of gas you really used, plus it had that extra 1/2 gallon of space from the previous fill up, or maybe more.

Now to MPG. The miles on top of the equation are what they are, but the gallons are not correct. The gallons you think it took are higher, so the mpg will be lower. Take your mpg calculation with a grain of salt.
 

·
Premium Member
Joined
·
2,262 Posts
Discussion Starter · #15 ·
I trust your math and I don't doubt that the pump is accurate in terms of you getting the amount of gas it says it pumped.
I'm sorry, I don't get your reasoning. If the pump shuts off the pump shuts off. The math is run based on the gallons sold. If the pump output is accurate so it the mileage calculation.
 

·
Registered
Joined
·
95 Posts
I'll try one more time before giving up. This time I'll use examples.


Starting point:

Tank is full, trip odometer reset to zero


Fill up #1
Trip Odometer: 210.0 miles
The pump shut off at the proper time, so the tank really is full.
Gas pump reading: 7.000 gallons
Calculated fuel economy: 30 mpg


Fill up #2
Trip Odometer: 210.0 miles
The pump shut off too soon this time. See explanation above again. There was 1 gallon more that could have been added to the tank to make it full, but it's just empty air space now.
Gas pump reading: 6.000 gallons
Calculated fuel economy: 35.0 mpg
You think the car is doing great, but if the pump had filled the tank properly it would have been the same fuel economy as Fill up #1.



Fill up #3
Trip Odometer: 210.0 miles
The pump shut off at the proper time, so the tank really is full, but remember last time? At the last fill up, it wasn't full because the pump shut off a bit soon. 1 gallon of space was empty. That gets filled this time.
Gas pump reading: 8.000 gallons
Calculated fuel economy: 26.25 mpg
You think something is horribly wrong with the car, but in reality it's the same fuel economy as Fill up #1.


When I fill my car the needle is typically a bit over full. I can drive roughly 30 miles before the needle even comes down to full. I have a mix of driving and average near 30 mpg, so that extra amount of gas above full must be around 1 gallon. If the pump shuts off 1/2 to 1 gallon early I probably wouldn't even notice. It would still show full on the gauge by my estimates. I don't think anyone else would notice either. Does anyone have a special scope or tool to inspect or measure how full the tank gets each time they fill up? Does anyone check this religiously?
 
1 - 16 of 16 Posts
Top