Sender unit in fuel tank not working

[NITEHAWK]

First--parameters: 1989 Foretravel Grand Villa 36' diesel pusher with 100 gallon tank. Chassis is Oshkosh truck. All dash gages are Morse brand. 67,000 miles on the rig. (apparently has set a lot)

Tank is mounted between frame rails about halfway back from front. It is rectangular, sits on a steel plate suspended by threaded steel rods from the frame. Sender will occasionally work when Coach is in almost constant use, but will only show 3/8 tank when full. Seems sender is stuck. Only access is to drop the tank in order to reach/remove sender unit. Got an estimate of $700 to repair and/or replace sender unit.

Good price?? It appears I cannot raise the coach high enough to remove tank here in driveway. Any ideas? Suggestions?

Thanks

[bluefox]

My sender unit was on the outside of the tank. Give Oshkosh a call an ask them.

[Kurmudgeon]

Although senders do go bad, it is far more common that fuel gauge problems are in the circuit between the tank and the instrument. Before going to the expense of replacing the sender, make sure the circuit is properly grounded and all of the connections are sound and clean.

Another issue is voltage. I have no way of knowing how your chassis is set up, but many instruments do not operate on 12 volts, even though the system is 12 volts. A service manual with a schematic would be very helpful, as it may show voltages and may show a voltage regulator in the circuit. A common voltage for instruments is 5.2 volts, which is supplied through a regulator which supplies that constant voltage regardless of battery voltage. That keeps your instruments from fluctuating as battery or alternator voltage fluctuates. If your system is regulated to a lower voltage, and the regulator is bad, it will affect whatever instruments it feeds.

Your description of a full tank reading only 3/8 could easily indicate too much resistance or incorrect voltage in the circuit. After doing some checking, you may find you have a much less expensive fix than you think.

JP

[Midniteoyl]

Mine actually shows way past Full whenever there's more than 20gal in the tank (80gal tank), then drops really fast to E..

[Mekanic]

Quote:

Originally Posted by Midniteoyl Mine actually shows way past Full whenever there's more than 20gal in the tank (80gal tank), then drops really fast to E..

on 73-87 Chevy pickup trucks the fuel gauge needle would point to the right at 3 oclock when the main wire would short out on something like the frame. (The gauge went from E at about 10 oclock to full at about 2)

What you are describing sounds like the same thing.

[Midniteoyl]

Ahh, thanks.. But wouldnt that cause it to stay 'Full'?

[Retiredblade]

When I bought my Islander, the fuel gauge didn't work at all. I pulled the dash, checked the gauge, it was ok. Got the wiring schematic to see what color and where the wires went. traced to fuel tank. Upon opening the LPG bay, I could see with a flash light the wires going to the top of the tank and sender, but no way to get to it. Then I went to the bay on the opposite side, carefully, and neatly cut a hole 4" by 12" in the back of the bay near the top of the plastic covering which covers the access to the fuel tank bracket bolts. With a flashlight I was able to see the the ground wire vibrated off! Put it back on and gauge works, ground wires are very important! I hope you don't have to drop the fuel tank, that would be a terrible, difficult job!

[Mekanic]

Quote:

Originally Posted by Midniteoyl Ahh, thanks.. But wouldnt that cause it to stay 'Full'?

only if the wire shorted out and stayed that way.
on many of the old truck you hit a bumps and the needle jumps all over the place.