Fuel gauge doesn't seem to work

[matrophy]

I forget the exact number but my 1986 720 fuel tank supposedly holds 13 - 14 gallons. When the gauge gets close to empty and I fill up, it only takes around 8 gallons for the gauge to read full. Therefore I'm never sure how much fuel I have  - either the gauge is reading full when it's not or reading empty when it's not. 

 

I did some general googling and it seems that Nissans may have lots of problems with fuel gauges and I'm wondering if that applies to my truck as well. If so, can I get any suggestions for trouble shooting and or what to do to fix it?

[datzenmike]

Fuel gauges on 720 are not known to be a problem but the fuel pump relay can be. This is not the same.

 

19 minutes ago, matrophy said:

  When the gauge gets close to empty and I fill up, it only takes around 8 gallons for the gauge to read full. Therefore I'm never sure how much fuel I have  - either the gauge is reading full when it's not or reading empty when it's not. 

 

 

 

How many gallons after the 8 does it take?

 

How close to empty??

[Charlie69]

I have owned all years of the 720 production and they all have had  2 to 4 gallons in the tank when the gauge is indicating empty.  This is a bit of a built in reserve to help you not run out of gas.  Live with it and fix something that really needs to be fixed.  Drive and enjoy your truck.  Basic maintenance keeps these trucks running for years

[matrophy]

Thanks Charlie. It is about 4 gallons that I must be short. Capacity is 13-ish gallons and when i fill up when it reads empty., I can only get 8-ish.

\

Mike, it only takes 8 when the gas station pump stops filling.

On 9/26/2019 at 8:27 PM, datzenmike said:

Fuel gauges on 720 are not known to be a problem but the fuel pump relay can be. This is not the same.

 

 

How many gallons after the 8 does it take?

 

How close to empty??

 

[Charlie69]

What I do with mine are carry a full 2 gallon gas can and watch the gauge, when it hits empty make a mental note of the mileage then keep driving untril you run out, check the milage when you run out.  This will give you a ruff idea of how many miles you have after you hit empty.  After putting in the fuel from the 2 gallon gas can go to the nearest gas station and fill up.  Add the 2 gallons to the amount showing on the pump and this will tell you the capacity of your tank.  All of my 2 wheel drive 720 king cabs have approximately 11 gallon tanks.  4x4 tanks are larger.

 

CAUTION!  If you have a dirty and or rusty tank donot run the truck out of gas as you could plug something up.  One of the first things I do when I purchase an old vehicle is pull the tank and have it professionally cleaned reinstall with all new fuel line clamps and filters.

 

 

[datzenmike]

Charlie the later, pretty much anything with L20B and on, have a fuel return line. This slowly but constantly circulates cool fuel past the carburetor. In doing this it is also being constantly filtered. This keeps the fuel tank much cleaner inside. As the pickup tube ends about 1/2" ? above the bottom of the tank any sediment is going to be sucked up any way. Only difference with a low fuel level is that anything that floats is now possibly going to be sucked in. 

[Charlie69]

Mike you have so much information on these cars and trucks it amazes me daily!

Thank you for all you help over the years.

[dhp123166]

I had issues with my non-functioning/ intermittently functioning fuel gauge when I first bought my truck.

 

Turns out the vehicle harness right before the fuel sender wiring was frayed.

Edited October 14, 2019 by dhp123166

[captain720]

The trucks just read empty long before they are empty, live off the top of the tank and you will be completely fine. I always keep track of mileage just for good measure.

 

The grounds might go sideways on you so just add in some extra ground straps and what not for good measure. My main engine ground fell off once and I didn't even notice because I have extra grounds running everywhere. 

[datzenmike]

On long trips I reset the odometer and keep an eye on it. My wagon is from Nevada but seems to have California emissions on it. It's at least 10 (Canadian gallons) or as much as 11 if California emissions. I get about 32 MPG (Canadian) so I use 30 MPG as a safe bet. That means I can get very close to 300 miles range.  When the odometer reads 250 I start looking for a gas station. I forget what the gauge reads at 250. Near home I just keep topped up.

 

Find out how much your tank holds.

At 1/4 go in a fill up, keeping track of how much it took to fill.

Subtract and this is how much you have in reserve.

 

Try 1/8 tank and do the same. Next time you get near 1/8 you know how far you can go before running out. Most Datsuns are about 9 Imp Gal or 13.5 US Gal. at 1/8 you should have well over 1.5 gallons.