74 620: Gas Gauge Reading @ Empty Tank

[Cardinal Grammeter]

I have to repair my tank and am trying to "sneak up" on running it as empty as possible.

 

I already have a tiny gap between the edges of the Needle and the E graduation - so how big a gap when actually empty?  (I figure a description in "needle widths" or the approaching "E" on the gauge.)

 

I was also thinking I should reinstall my fuel pressure gauge on my cowl since I think I would see the pump starting to suck air before I would notice any engine cutting out.

 

EDIT:  Reinstalled FP gauge.  Should be very helpful, when I hit zero pressure, I'll still have one bowl of fuel to get off the road safely.  (I've got  5 gal in a can with me for when that happens.)

 

EDIT2:  Went to do my chores and the FP gauge went to zero before I could get out of my driveway (truck pointed downhill slightly.)  So I added about 1 gallon and still no FP (truck still pointed downhill.)  I added at least another gallon and I got FP.  With 2-3 gallons added the Fuel Gauge needle is centered on the last graduation.  

 

NOTE:  I TOTALLY HATE damped fuel gauges.  BMW had undamped and you would see the needle flying about as the fuel sloshed in the tank.  When you got really low, you could "see" the needle hit bottom and then you could wiggle the steering wheel to slosh the gas around which moved the needle and you could fairly predict what you had left.  Running below a gallon was no problem.

 

DAMPED GAUGE:  I think I read that the damping is a drop of thick silicone oil on the needle axle bearing.  I've taken gauges apart and wonder if I could dissolve it away with solvent?

Edited September 30, 2019 by Cardinal Grammeter

[datzenmike]

I never have nor will I be running that low. There is no reason to and every reason not to. When I get below 1/4 I start looking for a fill up.

[Cardinal Grammeter]

I had a 4 hour trip into WV and I missed a fuel stop on the interstate.  I was shocked how quickly the gas gauge was going down and didn't think I could make the next fuel stop.  So I got off the interstate looking for a gas station as per my GPS, but it no longer existed.  Much drama ensued. 

 

From what I've learned, that worry was totally unfounded since you have fuel when the needle is a full width below the empty graduation.  (2-3 gallons still present.)

 

It's always good to know where Empty actually is.  Some people when they buy a car, put a can of gas in the trunk an run it dry to see where that is on the gauge.

Edited October 1, 2019 by Cardinal Grammeter

[DanielC]

Most of the cars and trucks we are driving are 30 to 50 years old.  In that amount of time, there is most likely there is trash and junk in the gas tank.  If you run the tank completely empty, that trash gets sucked into at least the fuel filter, and possibly beyond that.

If you have a more modern vehicle, with the fuel pump in the gas tank, or an inline fuel pump close to the tank, the fuel pump need liquid gasoline flowing through it to cool the electric motor that drives the fuel pump.

 

My dad had this advise.  "Keep the top half of the tank full, and you never need worry about the bottom half."

 

On my 521, the top half of the fuel gauge is not really accurate, but by a half tank, it reads pretty close.  When the tank is close to empty, the gauge reads empty.  When I first start the truck, the fuel gauge flairs a little high, and then reads a steady slightly lower amount.  If the tank is almost actually empty, when I start the truck, the gauge does not flair slightly higher, I know I need to make getting gas a high priority.