gregoret@cgl.ucsf.edu (02/23/90)
We're about to replace the fuel tank sending unit on our MGB. We are sure that the existing one is bad. In light of the fairly recent discussion about explosions and gas tank modifications, does anyone have any suggestions/precautions about how the replacement should be done? I think the current unit leaks a little when the tank is full. Is there a sealant we could use to leak-proof the new sending unit? Thank you, Lydia Gregoret P.S. About ready to sell the Honda and rely on the MG full time!
andyh@uunet.uu.net (Andy Haber) (02/26/90)
> > We're about to replace the fuel tank sending unit on our MGB. We are > sure that the existing one is bad. > > In light of the fairly recent discussion about explosions and gas tank > modifications, does anyone have any suggestions/precautions about how > the replacement should be done? > > I think the current unit leaks a little when the tank is full. Is > there a sealant we could use to leak-proof the new sending unit? > > Thank you, > Lydia Gregoret > > P.S. About ready to sell the Honda and rely on the MG full time! You'll be sorry :-) > > I sorta replaced the fuel tank sending unit in my 69 MGB about 2 years ago. What I actually did was to take it all apart and wind up putting the old one back in. Anyway the story goes as follows. When I bought the car, the fuel gauge did not work. The first thing I did was to take the gauge itself out of the dash and test in on my workbench. With a 12 volt power supply and the right resistor I could make it read any value I wanted, so I knew the gauge was good. One point of interest, reading approx. half full, the gauge would draw over an amp of current! Leave it to Smiths to make a fuel gauge that wants 15 watts of power just to give you a reading. Anyways, next I put my resistor on the end of the wires that normally go to the sending unit. Again the gauge would read according to the resistor used, so I knew the wiring on the car was good. Ok, so I send for a sending unit. This part sat arround for a while, until one day I noticed a leak in my fuel tank. The easy way to drain the tank is to unhook the fuel line to the carb. and use the fuel pump to pump the gas into a gas can. I didn't know how much gas was in the thing when I noticed the leak, but it turned out to be about 6 gallons requiring that I run off to an auto store and quickly buy a 5 gallon gas can to go with the 1 gallon can I allready had. Anyway, I pulled the tank out and took it to a radiator repair place and they fixed the leak. When I got it back, I was all set to put in the new sending unit, but then I got to looking at this new sending unit. There is a sliding contact along the side of what is basically a wirewound resistor. On the orginal, this is inside a small metal box which, when emersed in water, no bubbles come out, so I summise that no liquid gets in. On the replacement part, you can see the contact point between the resistor and the arm attached to the float. Knowing that more than an amp of current is going to be going thru that contact point made me say "Wait a minute. If this thing breaks contact and sparks while the tank is near empty, there is going to be a big BOOM!" I don't know if this would ever actually happen or not, but I'm not going to find out by experiment either! I put the old sending unit back in and to this day rely on other means to know when to fill the tank. First is the trip odometer, the second is an early warning from the after-market fuel pump that will start rattling like the dickens when it's not getting any fuel from the tank. My advice to others is not to buy the sending unit from Victoria British Ltd. like I did, and second, if the sending unit is not sealed in a box like the orginal, then don't buy it. Replacing the unit is not difficult. First drain the tank. The sending unit is held in place with a lock ring that rotates to release the unit. Mine came out with no problems. If the lock ring is stuck and tapping on it with something seems necessary, I would recommend that NOT use anything metal. A wood block should do the job. If you still have trouble, consider taking the car to someone else and let them do the pounding while you're a long ways away. Be careful once the old sending unit is taken out. Any sparks or flame at this point could ruin everything. Also do this in a well ventilated area. I forget if there is a seal on this or not, check the Moss catalog, if they sell one then there is one. Any sealant that can resist gasoline can be used to seal any leaks. -- Andy Haber (andyh@HWD.csd.harris.com) Harris Computer Systems Division, Ft Lauderdale, FL