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Gas gauge

This is a problem I notice on my Nissan Maxima and on my former car, Toyota Camry. When I fill the car, the gas level goes about 1/8 above the full line. The car goes almost 100 miles until the first quarter is used. The next quarter goes about 75 miles (total mile 175). The third quarter seems to go only about 60 miles and the final quarter is on empty within 50 miles.

First, why does the gauge go over the full gauge at the beginning? Why doesn’t it stop at full? Perhaps, this accounts for why I get 100 miles during the first quarter as I really have an extra 1/8 tank but then, why does the gauge depletion seem to accelerate and the second half yields fewer miles then the first half and the third quarter fewer mile than the fourth?

Remove the gauge float unit from the tank and bend the float arm upwards a little and the needle will now rest on the “full” mark when you fill the tank and be a little more accurate on the way down…

This has been pretty standard on every car I’ve seen (BMW, Toyota’s, Nissan’s, Ford’s, you name it). There’s no stop installed on the gauge (like the pin on the speedometer to stop it from dropping past 0). It’s an electrical connection to a variable resistor, and you can go through the pain Caddyman suggests if you like.

The float arms almost never actually float all the way to the top of the tank. There’s always some fuel above the arm at its highest point, so they’ll all go a while before the needle starts to move. IMO, it’s simpler to understand that’s the way fuel gauges all seem to work, and also realize it’s more important to know where the bottom of the tank is, rather than the top. If you run out of fuel when the needle isn’t on the bottom, then you could well be stuck somewhere.

It may take a bit of testing to get it right, as just adjusting the top will also adjust the bottom. The arm would have to be lengthened, and then adjusted. Too much aggravation for me to mess with. Just bending it may be a tad more accurate on the way down, but the bottom (eg, tank empty) won’t be in the same spot, either.

Every car I have ever owned from my 1947 Pontiac to my 2011 Toyota Sienna has a fuel gauge the behaves like this. There is not a linear relationship between the reading on the gauge and the amount of gasoline in the tank. As long as the fuel gauge gives a rough indication of the amount of gasoline in the tank (within 1/8 of the size of the tank), I am satisfied. At any rate, the fuel gauge, with its inaccuracies, beats having no fuel gauge as on the pre-1961 VW Beetles. On these old VWs, when the engine sputtered, you knew you were low on fuel and kicked the floor lever to go on the reserve tank.

I have yet to see a fuel gauge that is particularly accurate myself, which is why I always reset the trip odometer when I fill up. They are not scientifically calibrated instruments because they really don’t have to be, and making them as such would be cost prohibitive. Another variable is the shape of the fuel tank. Some of them are very oddly shaped, which will create further discrepancies in the reading vs actual quantity of fuel in the tank. All the gauge is intended to do is give you a rough idea of how much gas is in the tank to prevent you from running out.

Yep pretty normal. The only car I’ve had that didn’t do this was my 59 VW which had no gauge. Its just a potentiometer so it just registers where the float is as all. If the tank is so full that it takes a while for the float to start to move, that’s why it takes a while for it to register usage. When my Olds gets to 3/4 tank, it takes almost 10 gallons to fill it again.

Triedaq wrote:
Every car I have ever owned from my 1947 Pontiac to my 2011 Toyota Sienna has a fuel gauge the behaves like this.

For what it’s worth, the fuel gauge on my Acura MDX is very linear. I can guess within a half gallon of what I’ll need when I fill up.

@lion9car–Maybe the manufacturer of Acura chose the name of the car since the gas gauge is “accurate”. On the cars I have owned, the gauge drops slowly until it indicates about half a tank and then seems to drop more rapidly to empty.
Having played French horn for almost 60 years, I am used to transposing. I look at the fuel gauge and “transpose” the reading to what I think the amount of gasoline is in the tank.

My car does the same thing as the OP’s, but I never considered it a problem. It’s not like something is broken or will leave you stranded. With my car, I just choose to live with it.

Our Acura TL does the same thing. Takes about 50 miles to come off full, then drops accordingly. Don’t know why the MDX would be different.