Inaccurate or Erratic Fuel Gauge

This could be caused by one or even a combination of three things.

Common to almost all models from the 1950's to the early 2000's. Ever run out of fuel and you just knew your fuel gauge was reading at least a quarter of a tank. Never totally trust a fuel gauge on a 20+ year old car, especially on one you have just purchased! If you have an old diesel at least carry some spare fuel in the trunk.

Play Video

Problem & Solution

Common among these chassis:

Classic Sedans
W108 W109
W110 W111 W112 Sedan
W111 W112 Coupe

The problem could be caused by a faulty sending unit located in the tank, corroded or loose contacts on the wiring plugs, or a bad actuator at the fuel gauge on your dash. Start by locating the sending unit on your fuel tank. On the 114 or 115 chassis is is located under a plug in the center of the trunk floor. (Same on the 123 wagon) On the 123 chassis sedans and coupes it is located under the first aid box. On the 126 chassis it is located under a large plastic plug on the left side way under the rear seat back. The back of the seat must be removed to gain access.

If the problem persists after cleaning the plug contacts, remove the fuel tank sender for inspection and cleaning. Tip it up and down to see if the float is moving up and down inside the top. Try sloshing it in diesel fuel. You can take it apart but you risk the possibility of damaging it. Resistance figures are available from factory information but we can not supply that. If you are sure the sender is working properly then the problem may be at the gauge. The actuators can be replaced if you know the procedure.

Check our related products as we sometimes have good used fuel gauge actuators for sale.