So many things have been a problem on this car... same one as no start thread.
When I got the car it had been sitting several months. At first the fuel gauge didn't move; a friend said to fill it, and after a while/miles, it did start to read, and apparently accurately, Until about 1/3 tank, where the needle stops moving down. Putting gas in raises the needle. This has been consistent for months. So to me this is the sender being stuck. Would pulling it part way out and pushing on it, or similar, maybe get it going/sliding down and restoring function?
Or is replace sender the only way...

Threading got too hard so I am putting this here if anyone wants to read results.
I put in two large bottles of Techron; I hadn't heard anything else so thought I'd try it. Now I see Spook said the same thing.
In any case, the car sat for 10 days. No results, needle at 1/3 even after a couple miles driving. Then it sat another week. After driving a few miles, the needle Slowly went up to about 7/8, then after some more time went the rest of the way to full. So this seems actually Worse than before, as earlier the needle seemed accurate til 1/3 or so.
Due to the key issue which is not repaired yet, I am not driving the car so it'll sit some more.

Dear jerryc,

Hope you're well. If I've properly understood your most recent posts: (a) you filled the gas tank; (b) put in plenty of Techron; (c) let the car sit for a few weeks; (d) drove the car for only a few miles. As a result, the tank still is "full".

Before, the fuel gauge would not register anything above one-third full. Now, with the tank full, the fuel gauge shows "full".

So, when you switch-off the engine, does the fuel gauge needle drop to "empty"? When you turn the key to "on", does the fuel gauge needle rise from "empty" to "full"? Or, does the fuel gauge needle read "full" all the time?

If so - if the fuel gauge needs reads "full" - continue to drive the car. Does the fuel gauge needle drop, as gas is used? Or, does the fuel gauge needle stay on "full", even though the tank no longer is "full"?

If the fuel gauge needle drops slowly as the miles driven rise, then Techron has cleaned enough waxes and paraffins from the send unit's wire-wrapped rods, to restore fuel tank send unit function. If the fuel gauge needle remains stuck at "full", as miles driven rises, then the fuel tank send unit may be so damaged that it has to be removed and possibly replaced.

Hope this helps.

Yours faithfully,

Spook

THe needle Did read to full, sometimes taking a while to get there, but would never drop below 1/3.
After recent fillup/techron it did not read full til it was driven some miles.
So with the same gas/techron, I put 35 intown miles on. As said it was initially slow to get to full, but then did and seemed to read correctly, just below full. Today I went 140 mi on the highway, and it seemed to read correctly the whole time, slowly going down. Now with 180 mi it reads a little over half.
Yes the needle does go to 0 when shut off.
So I'll see what it shows as it gets to below half, and below 1/3 and will report back.

Dear jerryc,

Hope you're well. Thank you, for the encouraging report. If the gauge shows a slow drop past the 1/2 tank level, the Techron may have dissolved enough paraffins/varnishes to allow the send unit float to resume moving along the wire-wrapped rods inside the fuel send unit's barrel.

If so, I'd use another bottle or two of Techron Fuel System Cleaner, until the fuel gauge needle moves freely. When you switch-on the ignition, the fuel gauge needle should move quickly to whatever position is required.

While this Techron product isn't cheap, it is good value, if it lets you avoid pulling/replacing the fuel tank send unit.

Hope this helps.

Yours faithfully,

Spook

Dear jerryc,

Hope you're well. How much fuel was in the tank, when the Techron (fuel system cleaner) was added? How far did you drive, after adding the Techron?

Yours faithfully,

Spook

I filled the tank, it sat for a week to 10 days,then I drove it a few miles. The needle did not move. It sat another week, I drove it maybe 10 mi, and after 5 mi or so the needle Slowly went up, as said. So it's still basically full.

The good news is that the gauge and sender still work. Adding engine cleaner to the tank is a good idea and if it cleans off the sender wires, great. Otherwise, you could remove the sender and carefully clean the sender. With a volt meter, you could then test the 0hms or resistance as you move the sender up and down.

Only get a new sender when the old one is damaged beyond repair. I have cleaned a couple on 850's with great success using gasoline as a cleaner, with a soft brush.

Dear jerryc,

Hope you're well. Before pulling the send unit, get a couple of big bottles of Shell V-Power fuel system cleaner (each bottle should treat up to 20 gallons). When you're ready to fill the tank, add both bottles, fill the tank, and let the car sit for a couple of days.

The float - that registers the fuel level - slides along two wire-wrapped rods inside the send unit's barrel. Two "fingers" mounted on the float graze the wire-wrapped rods. That completes a circuit and provides a signal to the fuel gauge.

If the "fingers" and/or the wire-wrapped rods are coated with waxes (paraffins) and varnishes - common in gasoline - the float will not move smoothly, or at all. These waxes and varnishes are "sticky", which is the problem.

The solvents in the fuel system cleaner could dissolve some of these deposits, so allowing the float again to move freely.

If this doesn't work, the fuel system cleaner will still scrub the working surfaces - hoses, pipes, injectors, etc. - clean of crud, so there's still a benefit.

Hope this helps.

Yours faithfully,

Spook

Threading is so hard after a while, I hope Spook sees this.
I do not see Vpower available, except in fuel. Is there any substitute as good? Techron?

http://www.autobahnpower.com/products.asp?recnumber=92

Dear jerryc,

Hope you're well. Techron fuel system cleaner is perfectly fine. I'd use at the same time, two of the large bottles, each of which treats 20 gallons. I'd add these bottles just before filling the tank. The filling process and drive home should thoroughly mix the cleaners into the fuel.

Let the car sit for a day or two. This deliberate "overdose" - and some "rest" time - should allow the solvents/detergents to loosen paraffins and varnishes on the send unit's pick-up arms and wire-wrapped rods.

I'd then drive the car as usual. If the sender works properly, great. If not, repeat the treatment. If, after two treatments, the sender still does not work smoothly, I'd guess there's no choice but to replace it.

In either case, the rest of the car's fuel system will be squeaky clean. I add a bottle of fuel system cleaner every other year.

Hope this helps.

Yours faithfully,

Spook

Very interesting Jay, thanks. I did toss some Mystery Oil in earlier today before I saw your post.
I put 10 gal gas in, with the needle at 1/3. It then stayed there for a few blocks, then came up to a bit over 1/2, which I think is accurate. And after driving it did go down a bit so it seems to be at least as before, and headed to the 1/3 mark. I'll see if the MO has any effect, then try your idea.

Speaking of the car, today's lesson is that now the master cyl seems to be bad.
This makes;
rear end
shocks
struts
brakes
radiator x2 (a used JY one that was a year old failed after a couple months)
heater core
all seats
several window trim pieces
water pump
electric fan (had been 'converted' to belt fan)
steering rack
control arm bushings
stay bushings
door panels (in which I learned that 760 panels fit but don't have the vent to the side windows, so even More fun was had)
speakers
headlight
taillight

and misc other things I am forgetting. Dang. what a disaster.

This sounds like a pretty normal list for a 20 year old used car, once you catch up with the neglected maintenance you should have a nice dependable car.

Dan

I have had 16 or 17 Volvo's, 7 were/are 7/9 models. None remotely comes close to needing anywhere near all this, all at once. I think I have only replaced one master cyl, for example.
We'll see, it's not bad once it's running, but I actually prefer the ride of my 91 745 with stock original shocks, at 155k.

You have been lucky, I have put about an additional $1K plus in the first year of owner ship of my 5 - 240's. After that it's mostly routine maintenance and an occasional battery and set of tires.

Dan

Dear jerryc,

Hope you're well. If "Mystery oil" is indeed oil, it added viscosity to the gasoline, instead of solvents (viscosity-reducers) needed to dissolve waxes and varnishes, that coat fuel system surfaces, especially the fuel tank send unit.

I'd do a double treatment with fuel system cleaner, using two bottles for each treatment. The first treatment will - I hope - scrub the "mystery oil" from the system. The second treatment should remove from fuel system surfaces, the "gunk" present, before the "mystery oil" was added.

Hope this helps.

Yours faithfully,

Spook

I take it this is not the first thing you reach for...
http://www.marvelmysteryoil.com/

It is useful as a penetrant, although I prefer Kroil, even over PBlaster, and lubes better than WD-40, which of course is not primarily a lube at all but a Water Displacer. Many use it in the tank to keep pumps going, and it seems to have some effect on injectors but I make no claim to that. Many mechanics use it, in various applications.
I'll report back!

I agree with this approach. Its a PIA just r/r'ing the sender. I have been eyeballing one for the past couple days and it looked challenging to disassemble the barrel of the sender without damaging. Maybe if ya had one to practice on...lol. BG44k is great stuff.

Dear the rod,

Hope you're well. The challenge is to re-assemble the barrel's upper and lower sections, while keeping the float rods aligned, so they seat into the openings, at the barrel's lower end.

This is most easily done, if the float is jiggled, until it slides towards the bottom of the barrel. That moves the rods into place, and so eases fitting together of the barrel's halves.

Hope this helps.

Yours faithfully,

Spook

I'm going to try that also my gauge works just like yours.. I then found if I rap the bottom of the I'll get ti to read again until the gauge falls below 1/2 to 1/3 of a tank....

Thanks all...