We really don’t have to stress out the importance of the fuel gauge in a classic or any other car. Without it you couldn’t possibly know whether there’s enough fuel left in your old-timer for a stroll downtown. However the fuel gauges in old-timers are more susceptible to malfunctions. These are very delicate instruments that don’t take much to break.
Luckily, it is very easy to diagnose and repair most fuel-gauge related malfunctions with the help of a trustworthy classic car service in Orange County CA.
How Gauges Work
Naturally, not all classic car share the same type of a fuel gauge, but most of them based around the same principle. Every fuel gauge relies on two parts to read the fuel levels: the sender and the gauge. The gauge is located on your classic car’s dashboard and needs no further introductions. On the other hand, the sender is the part of the mechanism out of sight, located inside the fuel tank.
The sender determines the fuel levels by using a float connected an arm. This mechanism changes the resistance on a circuit that relays a signal to your dashboard based on how much fuel is left in the tank. Most old-timers use a scale of 30 ohm. This means that when the float reaches the bottom once the tank is empty, the sender will read 0 ohms and relay the information back to the gauge. The gauge then shows the tank is empty. In contrast, when the tank is refilled the float rises back to the top and sends a full signal of 30 ohm to the gauge. As the fuel level changes so does the electrical resistance level, allowing the gauge to show just how much fuel is left in your car.
The Gauge Always Showing a Full Tank
Most commonly, a malfunction in a fuel gauge occurs due to bad grounding. The sender must be correctly grounded so that the gauge can display the accurate fuel levels. There could be several reasons why your gauge is always showing the tank is full.
The wire connecting the gauge to the sender could be broken or experiencing connectivity issues on one or both of the system components’ ends. Additionally, the resistance wire in the sender could be broken or the sender could be improperly grounded if the tank is improperly grounded to the chassis.
There are a few ways to determine the source of the issue. Disconnect the wire on the sender and touch the chassis with it to ground it. If the gauge shows empty this means that the sender was not properly grounded or that it is broken and has to be replaced.
If this does not prove to be the issue, take a test lead and ground it to your classic car. Then connect it to the sending terminal on the back of the gauge. This terminal on the back of the dash is often marked with a red tag. If the gauge now reads empty, the problem is in the wire that connects the gauge and the sender. It could either be broken or experiencing a bad connection on either end.
Finally, take out the sender. Connect an ohmmeter to the sender terminal and the sender housing as you move the float up and down. The meter should show that the electrical resistance changing as you do.
If none of these tests points to an issue, the problem is likely in the gauge that needs to be repaired or replaced.
The Gauge Always Showing an Empty Tank
If your gauge is always pointing out that the tank is empty, there are also several likely causes you can try to rule out. The wire connecting the gauge and the sender could be grounded and shorting out the display. The short circuiting could also occur in the sender itself. Finally, there could be a hole in the float. In this case the float stays at the bottom of the tank as it becomes filled with fuel.
To eliminate these issues first disconnect the wire from the sender. If the gauge now shows full then the sender is broken. If not, disconnect the wire at the gauge. If it shows full then the wire is grounded and is causing the issue. If the wire does turn out to be the issue, repairing the issue is easy and cheap. All you need is a new wire to connect the elements.
If either the sender or the gauge are broken, we suggest contacting an expert Classic Car Service in Orange County, CA to try repairing or offer a replacement. Both are very sensitive pieces of equipment, especially in classic cars, and require an expert’s touch.