Low Fuel Light

[cornemuse]

'83 300CD. What is the fuel capacity?? My owners book says 21 gal. cap. yet I rarely add more than 16 gallons as the low light flashes & the needle is bouncing on the peg. Yesterday I fueled up at 19 gal & the light was (& had been) lit constantly for some time, made a detour to fill her up. (diesel = $2.83 - prem gas = $4.19, lovin' it !!)

Is the low light sensor in the tank sending unit, or in the guage?? Or is it a seperate system?

-c-

[anziani]

Cornmuse,
The sender unit is in the tank. You can see the top of it if you pull out the carpet. Anyway, the"low" light on later cars comes on at about 2 gallons remaining. And yes, when it gets towards the bottom they seem to go bonkers. My current car is OK but I was about to pull the sensor on my last and carefully clean it with solvent. It is a resistive circuit and I understand they eventually get crudded up.
I live North of you in the Coachella Valley. Fuel prices are usually better here. However, feel MY pain! I drive a 12 cylinder 390HP, '97 Coupe with a 27 gallon tank and get 19 per gallon on trips and almost nothing around town with the AC on. While you are saving money with your CD I am having the time of my life with this powerful "brute". How long does it take your CD to go from 80 to 135?
Anziani
'97 CL600 51K

[jaybutter]

I have an '84 300CD. My gauge reads empty at 16 gallons consumed but my low light does not come on until about 19 gallons used. When I bought my car I had to clean algae out of the tank and also the sending unit so I've had mine apart. There are two circuits in the sending unit, one for the gauge and one for the light. For the light, as the float bottoms out, contacts on the bottom of it complete the circuit for the low light. There is not much adjustment available and you run the risk of breaking the fine resistor wire for the gauge. So when my gauge reads empty I have about 100 miles left and when the light comes on I'm down to 50. Here is just one posting of many about taking the sending unit apart. Sending unit's out; how do I take it apart?

[Rocket99]

Originally Posted by cornemuse

'83 300CD. What is the fuel capacity?? My owners book says 21 gal. cap. yet I rarely add more than 16 gallons as the low light flashes & the needle is bouncing on the peg. Yesterday I fueled up at 19 gal & the light was (& had been) lit constantly for some time, made a detour to fill her up. (diesel = $2.83 - prem gas = $4.19, lovin' it !!)

Is the low light sensor in the tank sending unit, or in the guage?? Or is it a seperate system?

-c-

Those sender units are almost always the problem, they are pricey new, $250 or $280. they get mucked up like crazy so cleaning may be all you need. Be careful, there is a hair thin wire easy to break, finicky difficult to solder patch it back, though it can be done. I patched in thin copper which for the moment has done the trick.

its not too hard to refurbish, finicky to solder 46 AWG nichrome wire, you can buy enough for 125 sender repairs for $5 off ebay

the nut is 3mm X .5mm thread pitch

on mine the ground wire tab broke off. It attaches at the bottom of the plastic block unit at bottom, to one of the two exposed contacts at the bottom of the sender, that the float touches when fuel level is down that far, completes the ground to illuminate the dash reserve light that gets its "hot" at the instrument cluster. Use a 5 mm socket to remove the nut and plastic block at the bottom. To patch that tab back I used a piece of 14 or 16 ga solid copper, hammered it to a flat tab on an anvil, drilled a hole to it can be soldered to the copper around the threaded rod hole at the bottom WITHOUT TOUCHING THE ROD after its installed. soldered it on, then after its back on the threaded rod solder the ground wire back to the new tab.

I spent loads of time getting mine to work right, pleae feel free to get back with questions.