How do you test a fuel gauge?

[RobVG]

Can you just put voltage to it and see if the needle moves? Wondering if a full 12v will hurt it?


To test the sender I read you just move whatever float is has and check for variable resistance. Is that correct?

Thanks

 

[Shimmy1]

Most standard senders are a specific resistance range. I'm sure someone will come on here with the exact range, then you just measure the sender with a VOM. The gauge itself, if you can disconnect the wires, one terminal will be battery power, and the wire that goes to the sender is the ground. The sender adjusts how much ground the gauge gets to show a reading.

 

[Ronsii]

Hi Rob, yes the float moving up/down should change the resistance of the terminal on the sender unit.

Some electric fuel gauges put +12v to one side of the meter then the other side goes to the sender unit and the sender unit gives variable resistance to ground.

to test this type of meter all you have to do is ground the wire that would normally go to the sender and the gauge should go to full.

 

[RobVG]

Awesome, thank you guys.

 

[ScottAR]

Yep, the sender will be so many ohms full and so many ohms empty. Cycle the float up and down. If the meter jumps to infinity somewhere in the travel "she's dead Jim."

 

[RobVG]

Thanks Scott. Infinity meaning no continuity? It starts out that way on "Empty" and it reads nothing till it hits "full"- the stopping point, and goes and from 8 to 2 ohms quickly. Playing with the wires I got the gauge to peg at full and at empty. I assume it's good.

Now to find out if Thomas is still in business.

 

[Ronsii]

Yeah, your sender has got issues.... have you taken the sender out of the tank? you may be able to repair it... sometimes they get bent or worn where the sliding contact is, some senders are more or less generic and can be replaced by something from another make. if you can't get one from a dealer don't hesitate to post up pics of yours, maybe we can get something working

 

[RobVG]

Yeah it's out. I'll post a pic monday.

It's not bent, can't really see the contacts. Will take it apart further-2 screws

 

[nowing75]

What is it in? Maybe someone has a part number for it. Merry Christmas

 

[RobVG]

Thomas ProTough 2200. I have a parts book but Thomas uses it's own part numbers and there's nothing stamped on the sender.

A related question, the fuel tank has a lot of crud in it. I tried using a air hose to stir things up before I drained it. It didn't work because I can still see about 1/2" or more of stuff in the bottom. Is there any reason why I shouldn't use a garden hose and nozzle to flush the remainder out? I figured I could flush the water out with some diesel. Thoughts?

 

[Ronsii]

I've used garden hoses with water before, usually I will make sure the water is dried out as much as possible before I do a diesel rinse but probably doesn't matter too much as long as you get most of the water out.

back to the sender... did you rip it apart further? sometimes they have a cover with bendable tabs or rivets you can drill out that covers the wiper arm and resistance coil, the coil could be broke in one spot or the arm will get worn/bent away either by the pivot getting worn out or just plain worn out. I have rebuilt a few different designs before so just put some pics up when you get a chance if you cannot locate a suitable replacement.




Ps. if you do get it apart don't throw away any pieces no matter how small... cause if you really can't find anything to replace it with we may need to know exact lengths of the wire wrap along with what type of wire(gauge) or other tiny bitsthere may be... this can be got around by testing the gauge with a resistance box to simulate the sender and find out what ohm range the sender is but sometimes it's easier to replicate what was inside the sender first

 

[RobVG]

I had today off. I'll get up a pic Monday so we can be on the same page.

Thanks

 

[Delmer]

If you have that much gunk in the tank, I'd bet that the contacts are gummed up on the "rheostat", of course the water could have eaten the wires away to?

Water is easier to deal with than the junk sitting in the bottom of the tank. Be prepared to use a pressure washer, add gravel and blow that around to scour it clean if needed. Use a blower overnight, or a hairdryer to dry it out, after vacuuming whatever you can reach.

 

[Ronsii]

If you have that much gunk in the tank, I'd bet that the contacts are gummed up on the "rheostat", of course the water could have eaten the wires away to?

Water is easier to deal with than the junk sitting in the bottom of the tank. Be prepared to use a pressure washer, add gravel and blow that around to scour it clean if needed. Use a blower overnight, or a hairdryer to dry it out, after vacuuming whatever you can reach.

^^^^ Good advice that's pretty much how I go about these kinds of projects.

 

[RobVG]

 

[RobVG]

Well that's a nice surprise, Thomas is still in business and apparently manufacturing loaders.

New sending unit- $40

 

[Ronsii]

Well that's a nice surprise, Thomas is still in business and apparently manufacturing loaders.

New sending unit- $40

Wow!!! 40 bucks doesn't sound bad for a dealer item... are you sure that isn't just for the gasket... just kidding... but you never know... Oh that's right you said thomas not bobcat.