How to Select the Correct Fuel Gauge and Sending Unit
Here at New Vintage USA, our tech department receives all kinds of calls. By far the most common question for customers is “How do I get my fuel gauge to work?” In this article we will cover some of the basics so you can be well informed and select the right parts for your build and make installation as easy as possible. Fuel senders and gauges work together as a system like any other gauge, and this should help you before you run out of gas during your installation.
How Do I Set Up My Gauges to Work With My Tank?
The first thing we need to figure out is which fuel sender is in the tank. If you have the stock tank and sender, its relatively easy to find out. By using the chart below, search for your vehicle make and year. The corresponding ohm (O) range is shown. All fuel senders are referred to in ohms (O). This is the resistance to ground. All fuel senders are described with the EMPTY reading first and the FULL reading last. For example, a 1970s GM sender is 0 O EMPTY and 90 O FULL. This is referred to as a 0-90 O sender.
The fuel gauge used must match the sender. What that means is the ohms (O) need to be the same for empty and full on the gauge and sender. That is why you will see kits for GM that have a 0-90 O fuel gauge, because it will work with the stock GM 0-90 O sender. There are a couple of advantages to using a factory match gauge in a build. The most obvious reason is simplicity. Keeping the stock sender means you don’t have to hassle with dropping the tank or running a new sender wire. Just connect the gauge back up at the dash and you are good to go. One thing that we do at New Vintage USA is all our kits include a programmable fuel gauge so that you don’t have to worry about which one to use when selecting a kit. All the Phoenix and Direct-Drive kits are easily programmed to operate on virtually any fuel sender.
I Don’t Know What My Fuel Sender Is, How Do I Figure That Out?
Don’t worry, we are asked this every day. Someone inherits a build. You lost the receipt to the tank you had. It’s been a decade since you put the tank in and now you are finally getting it hooked up. These are all real-world scenarios that New Vintage USA talks with customers about every day. We do have a method to determine which sender is in the tank. It takes a bit of time, but in the end it's better than running out of gas in the middle of nowhere (with no cell service).
The chart below describes the various fuel sender ranges used for popular vehicles. Every tank is shaped differently, the vehicle may not be level and who knows how much fuel is in there are factors that make this an approximate test to get you to the right range.
We need to measure the resistance of the fuel sender. It’s easy, the most important thing you need to remember is the sending unit wire cannot be connected to the gauge. You can measure the resistance either at the sending unit directly or at the gauge (disconnected) by probing the fuel sender wire at the dash. What we like about checking it at the dash is:
- You don’t have to get under the vehicle.
- Fuel tank stays in place.
- You are measuring what the gauge is actually seeing
STEP 1: Set your multimeter on OHMs (O). Keep it on auto or in the <200 O range if a selection range is available on your unit. You don’t need an expensive multimeter to perform this test.
STEP 2: Ground one of the multimeter probes somewhere on the vehicle chassis/body/tank. Don’t forget your sender needs to be grounded too! We like to use some alligator clips to hold the probe in place or use as a jumper for hands-free working.
STEP 3: Probe the sender wire with the other end of the multimeter. This will display a number in OHMs (O). If you have another set of alligator clips these come in handy, especially when you are under the dash. Write down this number.
STEP 4: Here’s the trick to this. If you can approximate the amount of fuel you have in the tank, that will tell you which sender you have. There are two ways to do this:
If the sender is out of the tank, all you need to do is move the float up and down while measuring the resistance (ohms). That will tell you the whole story of which sender you have.
If the sender is in the tank and installed in the vehicle, we do have a workaround for that too. Our techs at New Vintage USA get this call either when installing the gauges or after the customer has run out of gas. To figure this out we need to know two things:
A. How much fuel is in the tank? B. What is the resistance (O) of the fuel sender?
Here are some ways to figure out your sender while its in the tank:
-Check the resistance (ohms) when it's full: Easiest method -Check the resistance when the tank is empty: Easy on a new tank before it's full -If you know how much fuel is in the tank, use the chart to see the resistance, BUT this only works with one of the previous two measurements
Now I Know Which Sender I Have How Do I Get My Fuel Gauge to Work?
Just like any gauge, the sender must match the gauge, or it will not read correctly. What that means is the resistance (ohms) range must be the same for the gauge and the sender. If you are using a factory gauge the way to go is to use a sender that matches that factory range. For example, 1965-1986 Ford Mustangs use 73-10 O fuel gauge and sender. If you are using a factory fuel gauge, your best bet is to use the factory OR factory match sender. Let’s say you are installing a 5.0L Coyote swap in your 1967 Mustang; you may be using a sender that has the pickup, return and pump integrated. You need to order one that has a 73-10 O sender. Then everything will work correctly.
The New Vintage USA team always recommends using a fuel sender range that matches the vehicle for one reason; if you forget what you have in the tank, or which gauge you have, all you need to know is what year/make and model vehicle you have (should be pretty easy, right?).
Luckily for our customers, New Vintage USA direct-fit kits ship pre-set for use with your factory fuel sender. All you need to do is wire them up and off you go! In the event a different tank and sender are used, no worries, all New Vintage USA kits have a programmable fuel gauge that you can change to suit your tank/sender combination any time you like. Just set your DIP switches on the back of the gauge, restart the vehicle and the range is now set!
Now That I Have Everything Working, Why Is My Fuel Gauge Pointer Bouncing All Over While I Drive?
Basically, your fuel tank is a big bathtub with a lid on it. Once it has fuel in there, the sender float is bobbing all over the place, which the gauge will react to that movement. While many fuel gauges are dampened with oil in the movement or electronically, some aftermarket units are not. If your gauge is bouncing around, its due to the gauge not being dampened. This may be by design, or it may just be old and the dampening fluid has evaporated.
Baffled tanks and fuel cells will reduce this bounce, but those are designed to keep fuel going to the pickup so the gauge was not a consideration.
Our techs don’t get a lot of these calls because all New Vintage USA fuel gauges are dampened by microprocessors that average the tank slosh. This gives you nice, smooth pointer movement that displays the actual fuel level in the tank without the annoying wiggle.
My Fuel Gauge Still Doesn’t Move; How Do I Check It?
All gauge systems, including fuel, are composed of three components: 1. The gauge, 2. The wire, and 3. The sender. We already know how to check the sender. The next thing to inspect is the wire. Leave it connected to the sender. When checking the wire, you should see a very similar reading at the tank and at the gauge end of the sender wire. Remember to check the resistance with the gauge disconnected from the sender wire. You will see one of the following situations when checking the wire:
Same or similar resistance (within a few ohms O): Wire is good!
Infinite or 1000s of ohms (O): This means there is a break in the wire because there is not any resistance. Sometimes it just easier to run a new wire from the tank back to the gauge and eliminate all of the guesswork.
Zero ohms (O): This means that the wire is grounded out somewhere (unless you have a 0-90 or 0-30 O sender). Inspect the length of the wire for where it may have rubbed at the firewall or along the frame. Sometimes it just easier to run a new wire from the tank back to the gauge and eliminate all of the guesswork.
Now that we have ruled out the sender and the wire, its time to check the gauge. We are going to simulate a simple sender by grounding the sender wire. Before testing, make sure the gauge has power and ground connected.
Turn the vehicle on.
Ground the sender wire somewhere on the vehicle.
- The gauge will peg FULL or EMPTY depending on which way the resistance runs. If the gauge is dampened, it may take a few seconds for the gauge to move all of the way.
- Release the wire from the ground. The gauge will move to FULL or EMPTY, whatever is opposite of the first test.
- If the fuel gauge has power and ground and did not move either way, that means the gauge is faulty.
This is the exact process our tech line uses at New Vintage USA to help customers with their fuel gauges. While its not complicated, with a little background information just about any builder should be able to get their fuel gauge up and running for years of enjoyment.
