I have a 2018 Nissan Sentra with 25k miles. I did an oil change about 2 months ago my tire pressure is good and there are no check engine lights and air filter was also replaced. I have noticed and have noticed before any oil change that the car mpg will go down drastically when the fuel gauge shows 150-190 miles coverage left on the remaining amount of fuel. Now everyone is telling it's because my driving style. I know it's not that cause when the tank is full my car will give me excelent milage. I drive the same way when tank is full and when tank is half. It's when the tank is half that the mpg decreases drastically. What can be going on? Is something wrong with MAF should I reset it. It almost feels like the computer kicks in at around half tank thattriggers the mpg drop. Any advice would be appreciated.
Fuel gauges are analog, not digital. Try setting your trip meter and then dividing by the gallons you put in to fill up.
You may be expecting your fuel gauge to be more accurate/linear than it is. My Matrix goes 200 miles on the indicated first 1/2 a tank, then 100 miles on the indicated second 1/2 tank, and pretty much every Toyota has been like that. But my Matrix is getting 30 mpg all the time (more like 38 on the freeway).
I will try that however it's just such a drastic drop. For example. I drop my daughter off to school a mile away the tank when full at 370 miles range will barely move however when the tank is half the gauge would show as if I drove 10 miles. For example today when I turned my car on it's was showing 199 miles coverage. I barely drove 20 miles and now the gauge is at 125 miles. Makes no sense.
You may have a problem with the sensor that sends the fuel level signal - many cars, it's part of the fuel pump assembly.
Woildt I get a check engine light or something. I connected it to a code reader and there were no codes and would't the sensor send bad signal when the tank is full?
No, it wouldn't throw a code. I suppose you could check it with a multi meter, but it sounds more like it might be a case of the float/bearing or sensor sticking ( it is sitting in gunk from our wonderful ethanol-laced gas).
But why would it do it half tank are u saying that as fuel level reaches near the gunk the mpg drops? Will fuel injector fluid clean it up ?
No, I'm saying that there is a physical float that move up and down (like the float in a toilet), and then that turns a potentiometer up and down that changes the analog signal to the meter. There may be some cars with higher end sensors that send info into a trip computer, but the Sentras I've rented didn't appear to have that level of sophistication.
Look at this to get an idea of what I'm talking about
https://www.youtube.com/watch?v=5c5du1FanzA
Looks way more complicated as a DIY but with only 25k miles and fairly new car will I have an issue like this
I got in the habit (motorcycles didn't use to have fuel gauges) of setting my trip meter to 0 when I filled up. I have accurate info on how full the tank is, and if I'm getting good gas mileage. Cheap, accurate, reliable.
You have a relatively new vehicle.
I would check the mpg using the method Glen provided (full tank to full tank).
Refuel when the fuel gauge reads 1/4th tank and reset your trip meter to 0.
You can try it two times, once all city driving and once all highway driving.
Remember the range (distance to empty) values are only a guesstimate and should never be taken as gospel.
I understand that the gauge is not accurate and not considered as gospel but that guage is what I rely on when it comes time to fill up. What will reseting the meter do though? I mean the fact remains that something is up when the tank goes to half tank I watch the needel on the gas gauge and I definitely see the tank heading to empty much quicker then when it's full
That happens in most vehicles. Justin explained it in his post. Resetting the trip meter is to check your real world gas mileage on a full tank.
Your car's gas tank probably isn't a nice, rectangular container like in a truck, or an old school, large American car. They had to cram a 12-16 gallon tank into the body of a subcompact car and mold it to fit around other parts/ below the trunk. The tank is probably wider up top than down low, which will make the level seem to drop faster as you drive.
The gauge is a rough estimate. Refill when you get to a quarter tank and make Note of how much gas you put in, then compare with your owner's manual.
Some cars actually can read the fuel tank level on the PCM. I noticed my 2017 Mustang can. I had a problem with my EVAP system a while back that kept shutting off the pump. I watched the sensor read-out while putting gas in the car. It was put in the ON Position, not actually running.
You mentioned EVAP is that a rectangular shaped part that is located under the car next to exhaust? If that's the one then yes it was recently replaced. My wife had a car accident and the park broke. Can that be causing an issue?
The EVAP system is made of multiple components. The part you're referring to is the charcoal canister. It absorbs gas fumes instead of letting them vent to the atmosphere. That's connected to a long hose and a purge valve, which vents the fumes to the engine for combustion. There's a vent valve for when you're filling the tank up, it lets regular air flow out of the tank. Your gas cap also seals the tank. If you had a problem with the canister, or practically any other part in that system, your car will trigger the check engine light. The charcoal canister is emissions control device and the EPA is quite nitpicky about fuel emissions.
So what all u r saying is there is nothing wrong with the car and I am not understanding the calculations. It's just very strange that I drive the same way with full tank and quarter tank and almost the same distance everyday but at half tank the needle goes to empty very fast because canister is smaller at the bottom.
It doesn't sound like there's a problem. I would just fill it up around 1/4 and then you can fill up around 1/2, look in your owner's manual and compare what you put in with the indicated amount.
My truck has a wonky sending unit and won't read the right level half the time, but it's also 23 years old with over 280k miles. I picked a mileage on the trip odometer (270 miles) and I fill up at that point.
I have a 2018 Nissan Pathfinder which I just drove as we speak to drop kids off to class which is a mile away. My fuel gauge was showing 37miles and it did not move one but not did the digital display