I see you answer a lot of the questions Frog. Here is my question: I posted before about red gauge light coming on when the tank was full. Here is what I since discovered after reading all the posts. Great helpful tips and diagrams.

When I start the bike in my air conditioned garage the light is off. (Gas tank full) after the bike warms up and I drive it a short distance then the red light does come on and stay's on. (Rats)!

If I turn off the ignition and then restart the light still stays on. Do you have any thought's or fixes in mind that I might try? Or anyone else? The sender unit must be in the left front side of tank, I don't see any mech. arm at the rear of the tank but I will check again in the morning. On Aug 13, 2012



Thank You BMW Guru!



Dino

It`s a separate wire for each lamp, one brown/white and a brown/black.
Check if one of these wires are shorted to ground.

If the indicator lamp goes off when you disconnect the connector to the tank,
the problem is at the level sender itself.

Inge K.

dinos might not apply but I had a piece of copper wire inside the tank stopping the float banging on the tank giving the 7 ltr warning light to act as if it was possessed
had been like this over 10 years PO was told there is a short somewhere. I only found it after fitting a fuel gauge and could only get half a tank reading full suddenly going to empty
hope this helps cheers
Tony

Since Dinos don`t see any float arm inside the tank, I`ll guess he have the older type of level sender.

Inge K.

Inge I never saw a float either as it blended so well with the tank as a rigid part , I had to disassemble fuel cap and get hand inside to find the float wedged down the side of the tank
Tony

The old style fuel level indication works with temperature sensors. Normally the fuel cools the parts and when the fuel level drops the temperature increases and the light comes on. The two elements are fitted in a tube which is fitted between the two fuel connections and which holds the electric connector for the pump and sensors. It could be possible that the fuel does not come in contact with the elements as the holes in the tube-part are blocked or possibly a solder connection has broken loose?? Your aircon throws any argument a bit.....

just guessing ....maybe the sensor is floating around in the tank ?

Rene,

I do have what looks like a tube that angles across the tank. I will check that for blockage.... There was a lot of sludge in the tank before I cleaned it throughly. (The Tank)



Dino

With the old style sender unit I assume the temperature changes the resistance in the sender, and that this change in resistance is used to switch the light? If that is the case could a dirty (high resistance) connection in the loom cause this problem? Seems that moving the bike out of the warm shed into the cold outdoors is switching the light.

Greetings Everyone.

I drained the Tank, looked inside. There is a tube (1/4') that starts just in front of the fuel tank opening, it travels to the bottom of the tank, another one comes back and exits into the fuel cap vent hole. I believe this acts to keep the tank from a vacuum situation.



There is no float assembly at the rear of the tank, no float arm along the right side of tank.

In front of the fuel pump (left side forward) there is a black 4" section of tubing. Two wires come out and feed power to the fuel pump. I can see four wires coming in though. I must assume from other posts that this houses the thermister assembly that turns on the fuel gauge lights. At one time the yellow fuel gauge light also worked but not now. Just the red. I believe the red one meant you were really low on fuel.



P.S. In My other post I didn't call Crazy Frog by his handle. I meant no disrespect. I feel he is more like a Wise Sage, a BMW Guru. Because is answers are really helpful. The same to all the other members. I appreciate all the help that the members supply to help keeping these old k-bikes on the road. I think the k-series was the best that BMW put out the door. Not to say the new K-bikes are not cool. Who doesn't appreciate 165 H.P.

I know how nicknames can stay forever though. My nick names have been Wildman, Crazyman, Big-D, and The Don.

No worries mate, lets get it fixed. The two-light version has a 7 ltr and a 4 ltr remaining light (which are not too precise).
If you screw the tube out of the tank you will find it has two halves (in the sensor section). Take it apart and have a good look and let us know. Good opportunity to clean the contacts in the tube part as well!

Thanks Renez,

I pulled the tank off and really got into it! I cleaned it out, found two loose nuts from a previous change out of the fuel pump mounting bracket.

I unscrewed the fuel return valve and removed the ball and spring assembly to stop that buzzing noise. Drove me crazy! Those tips on what to do were just what I needed. I always drain the tank when pulling it so won't worry about not having the spillage.

Today I will pull the assembly to get at the sensor assembly.

I hope this discussion will help others when trouble shooting their bike.

Tiz good you found those nuts because they are stainless and that and Aluminium with a touch of water will put a hole in a tank faster than you can say it.

Well I pulled the black stick. It was gunky at the base. I cleaned it with carb cleaner. Then I pulled apart the black tube. The solder connections look good. The wires are undamaged.

The thermistors are red/orange and do not appear to be burned. I cleaned the two tiny, tiny holes and will fit it back together.

Will give it a chance to see if it will work any better.

The holes are smaller that a push pin that you use for a cork board to pin up your messages.

Well that's it. Must be beer time!

Dino