MG MGB and MGB GT Tech Talk
Help!!! I have a gas guage that will show full when I fill up with gas but about 5 miles later it will show half then in another 5 miles it will show empty. If you try to fill it up it won't take much gas because it is fairly full.
It's getting pretty good gas mileage..but would really like the gas guage to work.
How old is your sending unit? Sounds like it has holes in the float and filling up with gas.
It'll be on the passenger side of the tank attached to the sending unit. Raise up the car on that side (to cause the fuel to slosh to the driver's side). Then using a brass punch and hammer, you can rotate the locking ring. I say brass because of the chance of sparks and gas. Having said that, I've always used a flat head screwdriver and a hammer.
I can't remember if it's clockwise or counter, but you'll see how it turns. Then remove sending unit/float.
It'll be best to wait until you're low on fuel. If the float is old, it can crack, fill with fuel, then read empty.
I keep a couple of 5 gallon plastic gas containers around for draining the fuel. Undo the drain plug in the center of the tank and drain it into low plastic container and funnel into containers. If it's easy to drain the tank and if you have the tools you won't be tempted to do repairs with gas in the tank that should be done with the tank empty. Steve F. is probably right but there is also a full diagnostic path on the gas gauge using your multimeter at Paul Hunt, Solihull, UK site. mgb-stuff.org, I think. Do search for his name on this site or on the UK BBS. Look under electrical and gauges on his site in the Hammer & Spanner section, I think. I would think if everything tested out ok electrically then it would have to be something mechanical such as Steve describes. It certainly sounds like what he describes. I think I just get a kick out of using the multimeter like I actually know something.
Looks like th esender is shot. Run her a couple hundred miles after a fill and the gas will be low enough you don't have to worry about it when removing the sender. The retainer ring turns counter-clockwise to remove.
If you do order a new sender don't forget to get a new seal too. Installation is seal, then sender, then lock ring. Moss's catalog shows the wrong order of assembly.
And while you're down there working, check all the flexible fuel hoses, they may be in need of replacing.
