Interesting Fuel Gauge Behavior

[burnout8488]

I tried to fill up the gf's 97 850 GLT tonight for the first time. (133K) Her father previously owned it, and I don't think anyone has ever filled it up full. They're the type to go to the station and "put $20 in," never taking it to the full 18 gallons. More on that later...

The gauge said it had about 3 gallons, at the station the tank would only take 13 gallons before clicking off. I tried moving the nozzle in and out but the tank refused to take more. The gauge now reads ~16 gallons, which makes sense.

I'm wondering now if:

1) The tank really wasn't at 3 gallons before I filled it, and the gauge reads 2 gallons low? (unlikely because the light has come on before @ 2 gallons and they have never run out of gas)

2) The sending unit hasn't been @ "Full" in YEARS and the contacts are corroded there on the sending unit? (Maybe it's inaccurate throughout the range? But it still seems accurate when the fuel is low...)

3) There is something causing the tank to "click off" before actually being full? The tank filled up great all the way up until 13 gallons, then it simply wouldn't take anymore. Is there some sort of vent I should be locating, or a cracked hose that can cause this? There are no EVAP leaks, no fuel leaks, no EVAP codes, and no fuel smell ever, empty or full. It just seems like I can't get the tank to 18 gallons. (Per the gauge) Tried two different gas stations.

Replacing the sender looks easy, but it doesn't make sense to me that it failed right now. Thanks for any insight you guys can give...!

[misha]

...It just seems like I can't get the tank to 18 gallons. (Per the gauge) Tried two different gas stations.

The fuel tank holds approximately 19.3 US gals. (73 liters). When the warning light comes on there is approximately 1.8 US gals. (8 liters) of fuel remaining. If the ignition is switched on while refueling, the gauge may read inaccurately for up to 45 minutes.

I also had the problem with my fuel gauge which acted strange a long time ago.From time to time it will light up a "low fuel light" and needle will drop to zero after filling up the tank to the top.After i turn engine off and on ...the fuel gauge acts normal.That was about 10 years ago and happened a few times.

About a month ago he said "Hello" to me again.

This time guel gauge read a proper level of fuel but the "low fuel light" was on.After turning the engine off & on,it worked normal for a few minutes....and so on and on and on.

I decided to pull it out from the tank,disassembled it,cleaned it up....re-assembled it and put it back to it's place.Here is my topic:
https://www.matthewsvolvosite.com/forums ... =1&t=56052

[burnout8488]

Thank you! I had no idea what the sender looked like so that gives me confidence it's a piece of cake job. So the contacts are easily accessible and can be cleaned? Do you wire brush them, sand them, or just flake off "corrosion" or whatever builds up?

Now that I think of it, when I had the car at the dealership to have the mileage read out of the cluster using the Volvo VST tool, the tech noted that the cluster had a stored code. It was something about "fuel level reading too high," stored at a mileage right around when I threw a few gallons in a week ago. Your info, combined with this VST code makes me confident the fuel sender is probably sending wonky readings.

[cn90]

Add a bottle of Techron here and there and fill it up to at least 3/4 each time.

[misha]

...So the contacts are easily accessible and can be cleaned? Do you wire brush them, sand them, or just flake off "corrosion" or whatever builds up?

Only the bottom one.On the picture you'll see the bottom of the fuel level sender,little pliers(green) and nitro solvent(yellow).You must separate those edges(red arrows are pointing to them) in order to open the fuel level sender:

When you open it,just gently clean the corrosion,or some gunk which look like corossion,with a clean cloth & nitro solvent or petrol,close it and turn the whole unit upside down and back a few times to develop a free movement inside of it.After that you can put it back to its place.When you putting it back to its place put a thin layer of vaseline(petroleum jelly) on the rubber seal on the top of the unit.

That's what i did and no problem since.

Now that I think of it, when I had the car at the dealership to have the mileage read out of the cluster using the Volvo VST tool, the tech noted that the cluster had a stored code. It was something about "fuel level reading too high," stored at a mileage right around when I threw a few gallons in a week ago. Your info, combined with this VST code makes me confident the fuel sender is probably sending wonky readings.

Yes...the cluster can store the code about it,but if the code was "fuel level sender open circuit(shorted to ground)",then it is bad.

[burnout8488]

Add a bottle of Techron here and there and fill it up to at least 3/4 each time.

Think it might fix it without having to take the sender out? That might be a swell idea since my GF lives 2 hours away currently and she's only home every few weekends. Time to work on the car is slim, so if I don't actually have to pull the sender that would be wonderful.

We've been driving it around this weekend, and the needle was pinned exactly where I left it (around 16 gallons) for a long time. It only started to go down after about 60 miles, so it seems like it's just stuck there even though the tank was full. I also confirmed with her that her father would only splash in a few gallons at a time. The car hasn't had a full tank of gas in YEARS.

[burnout8488]

Misha - great tips, you almost make me want to go out into the parking lot and try it now. Seems too easy. Only problem is, I'd have to use chap stick on the o-ring

[Stewart05]

Thanks for the information Misha. I have a different but similar problem. When the gauge reches below 6 galons it stops measuring for a while. Then it goes up after a while I fuel it to 18 gallons and the it work well.
I´ll try dismatling and cleaning it. Thanks!