Adjustment on fuel tank gauge

S

sailingdeacon

Member III
Incorrect fuel tank gauges seems to be common problem. My 1987 E34 tank is supposed to hold 30 gallons. When I fill up the gauge will move only slightly until I crank up and then it moves begrudgingly to close to full but not quite. I use 11 gallons and the gauge shows slightly less than half full. Remember the tank should hold 30 gallons. I think I recall that using more than 11 gallons did not cause the gauge to fall any less quickly. So does this mean I can go to an empty reading and still have 10 gallons left? The tank is oddly shaped but there is a larger area toward the top.

The E34 manual says the gauge is a "mechanical float type with magnetice drive... a direct reed type." Is this a type with an arm which must be adjusted? If so the adjustment is done by removing the sender from the tank.

BUT...the E34 manual also says "the magnetic drive feature allows the gauge to be changed without removing the unit from the tank" What in the world does this mean??? Does it mean by "changing" the gauge to adjust it without removing the unit from the tank? Some sort of external adjustment? A screw external to the gauge??

Assuming I can adjust it, any suggestions on how to display 30 gallons from empty to full? My only thought is to try to have a full tank show beyond the Full mark.
 
J

Jim Baldwin

Member II
Check ground wires

A magnetic sending unit is just another way of saying that it has an electrical sending unit that functions using an electromagnetic switch. This is actuated by a mechanical float.

Without specific technical information, I would look for an adjustment screw somewhere on the body of the guage, (and only because it says it supposed to be adjustable).

Before you pull the sender or start taking things apart, you might check the wires and their connections. All twelve volt stuff is very sensitive to good clean connections and good grounds. A little corrosion or resistance on the ground wires can play tricks on gauges.

You could also assume that the gauge worked properly at one time so, what could go wrong? An simple adjustment of the gauge should have been done years ago, so I doubt if that's your problem.

Next, pull the sender out and play with the float. Move it up and down while looking at the gauge. It should give you an idea how it's working (or not).

I know this isn't the easy answer your looking for... Someone else will probably reply with the specific solution.

Good luck
 
S

sailingdeacon

Member III
Thanks so much for the very helpful information. Digging under the aft cabin bunk, I found the sender unit. No external adjustment. I removed the sender and it is a typical sender with an arm that pivots up and down for a 9" vertical span. But..... I found that the adjustment lockdown screws were loose and the sender was wobbling around. I checked the dimensions of the tank and the sender arm is positioned just over at the deepest part of the tank and the tank is about 9" at that point. After tightening the arm screws, the gauge is now at complete full. Turning off the power sends the gauge to full empty. So it now may be that the correct measurement will be shown and I can count on a 30 gallon measurement. I'll post the results later. Perhaps this will be of help to someone. Looks like Ericson provided for the best in this also!
 
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