The temperature gauge on your car is a fairly basic tool though it is an extremely important one and it can be very frustrating when your temperature gauge is not working. The technology has changed little from even the oldest models of cars and essentially its job is to do exactly what it says, it tracks the temperature of your engine. When it’s not functioning as normal you are going to be faced with three possibilities: the gauge is too cold, the gauge is too hot, the gauge keeps moving up and down the scale. That’s all assuming your engine isn't cold, hot or inconsistent. If your temperature gauge is not working, there are some things you need to know.
Why Is My Temperature Gauge Not Working?
The first thing you always need to look at with a strange reading on your temperature gauge is giving a strange reading is the actual temperature of your engine. Always rule that out first before focusing on the gauge itself. If you know the engine temperature is not an issue, you probably have to deal with one of these problems;
- The temperature sensor/sending unit is faulty. If this is the case your sensor will be reading the coolant temperature incorrectly and sending the wrong signal to the gauge. This could work in either direction and read as cool when it’s running hot or hot when it’s running cool.
- A malfunctioning circuit in the temperature gauge
- Faulty wiring is a potential culprit, and it can be traced to several spots in the whole system. You can have broken wires leading from the gauge itself to the sensor or wires from the sensor to the engine control unit. It’s potential that any wire along the path could have come loose, corroded, or been somehow broken that would cause your temperature gauge to stop working. A multimeter can help you diagnose this issue if you’re comfortable working with electrical systems. If not, then let your mechanic handle it.
- A contaminated coolant system will cause inconsistent readings and requires a full bleed of the system to repair. If you have air or something else in the lines, your gauge will probably be reading up and down as it passes through or stay cold if air bubbles get stuck on the sensor itself.
- A broken thermostat will throw your temperature gauge off. Because the thermostat restricts the flow of coolant through the radiator, it typically gives accurate readings of the temperature. However, if the thermostat gets stuck open and is no longer able to restrict the flow, it may continue to read cooler than the actual temperature. That doesn't mean your gauge will read stone cold, but it likely will rise very slowly and not reach as hot as it should.
- Corroded connectors at the sensor, the gauge, and the engine control unit can cause faulty readings. You may be able to diagnose this yourself if you can get a look at the firing and see where everything connects. A spray of
- The entire temperature gauge is faulty. This can be more problematic than it may sound like at first. In modern cars, the temperature gauge is a fully integrated part of your instrument cluster so it can’t usually just be popped out and have a new part you bought at Walmart swapped in. It’s possible you could get under the hood and look for bad solder points and wiring, but if you’re not comfortable with work like that then definitely taking the car to a mechanic is a good idea that can save you a lot of money in the long run.
- It’s possible a broken engine control unit could cause your temperature gauge to not work properly but this would be very rare and likely would have other symptoms as well. Still, if all else fails you could use an OBD2 scanner to check and see if this is the root of the problem.
The problem with a temperature gauge that doesn’t work properly is that you can’t tell which of these reasons are causing it to be faulty. You’ll need to do some digging, likely with a mechanic, to find if it’s the engine or the gauge itself that is giving you the readings. But there are some things you can do yourself.
How to Tell If Your Temperature Gauge Isn’t Working?
Without a proper diagnostic it can be difficult for the average car owner to know definitively if the problem with your temperature gauge is the gauge itself or the engine overheating. There are a few tricks to help you narrow it down on your own without paying money to a mechanic, however.
- Run the engine for about 20 minutes to get it up to temperature or until the gauge says you’re running hot.
- Open the hood and take a look at your coolant tank. Most tanks should have two lines marked on them, the top one reading as “full/hot” or something very much like that. Your coolant should be at that line after 20 minutes of running. If you have low coolant, that’s a clear sign you just need more and may have a leak.
- Your coolant should be green or orange depending of course on what color it was when you added it. If your coolant is looking cloudy, rusty, or muddy in some way then it has become contaminated and that means it could be causing your engine to run hot.
- When your engine is cool enough, check the radiator cap. A loose cap can lead to inconsistent temperature signals.
- Check to see if your cooling fan is running. After 20 minutes it should have kicked in, as it’s set to turn on around 230 F. If the fan is not running at this point, you’ll be reading hot because it’s overheating.
- Check the upper radiator hose which connects the radiator tank to the engine. It should be hot to the touch.
- Do the same touch test on the engine head near the thermostat. This should also be hot to the touch.
- If you have a cool/warm hose but a hot engine, then you may have a clogged radiator or a malfunctioning water pump. It’s also possible your thermostat is stuck.
- If the hose and the engine are both warm, then that is almost definitely an issue with your thermostat being stuck.
- Check your lower radiator hose compared to the upper hose. It should be cooler than the upper hose. If that’s not the case, then you have an issue with coolant circulation.
- Any coolant leaks you see will also lead to overheating.
All of these tests will help you determine if it's your engine that’s overheating. If you can diagnose these yourself, then you’re closer to figuring out the problem. But if none of these apply and your gauge is still reading very hot, very cold, or fluctuating in a way that doesn’t align with what you've seen under the hood then it’s possible the problem is with the temperature gauge itself. Sometimes the best way to figure out what’s wrong is by figuring out first what isn’t wrong.
What To Do When Your Temperature Gauge is Not Working
Checking your temperature sending unit is a good first step in determining if and why your temperature gauge is not working. The sending unit is not that hard to gain access to than the gauge itself and, on average, is more likely to fail. To test it you will need a multimeter so if you don’t have one then your next stop may be best made at a mechanic. If you do have one or can get access to one and are comfortable using it, then you can go ahead and try to measure the unit’s resistance on your own to see if it is functioning normally.
How your temperature sending unit works depends on your make and model. Some models have two units, for instance. Older cars will have the unit connected directly to the gauge while most cars from the mid-90s onward have the electronic control unit as the intermediary between the two. Check your manual or Google your make and model to find out exactly where your temperature sending unit is if you’re not sure. There are a number of sites online like this one that offer a wide range of manuals based on make, model, and year. Testing is fairly simple.
- Unplug the sending unit connector
- Use your meter to measure the resistance when your engine is cold. The resistance should read as high. Reconnect the connector.
- Run your engine until it gets up to temperature, then measure resistance again. At temperature, resistance should be low.
- Check your readings against the specs for your vehicle listed in the repair manual for your make and model. If the readings match up, you know that your sending unit is working properly. If not, you know that’s the source of the problem.
If you don’t have a multimeter handy but still want to check the sending unit, there’s a second method you can try as well.
- With the ignition turned on, connect the green wire from the temperature sending unit to the ground, like a jumper wire. If your gauge reads hot, then the sending unit is not functioning properly. If it doesn’t move, you can try the next step.
- Remove the green wire from the back of the gauge itself this time and connect a jumper from the back of the terminal to a ground. If the gauge is reading hot, then there’s a problem with the wire having an open or bad connection. If it doesn’t move, then you go to the next step.
- You can use a test light by grounding one end and connecting the other to the positive side of the gauge which should have a pink wire connecting to it. If there's no light, check the gas gauge fuse.
- If the fuse is good, connect a jumper between the ignition and the positive side of the gauge. If it works, you need to replace the wire between the ignition and the gauge.
- If the light turns on, then you’re running 12 volts, and it’s the gauge itself you need to replace.
Obviously, these steps get a little in-depth with electrical systems in a way most novices would not be comfortable with and you don’t want to attempt any repairs or diagnostics if you aren’t 100% comfortable with your ability to do so. If any of these seems too advanced, you’re going to want to check with a mechanic instead just to be on the safe side. Likewise, if you attempt these steps but still can’t resolve the issue, a mechanic will be the best option you have.
What Does it Cost to Repair a Temperature Gauge?
As we’ve seen there are a handful of reasons your gauge itself could be malfunctioning and that means a handful of potential repairs and associated costs. The average cost of a coolant sensor replacement, for instance, is around $200 to $270 depending on where you live and the make and model of your car. A faulty thermostat will have a similar cost in terms of parts and labor as well.
Do I Need to Fix My Temperature Gauge?
Some might argue that if it is the gauge itself not working and the actual engine is running fine, then there is no need to repair the gauge, or at least no need to prioritize it. This line of thinking could be very dangerous in the long run for your safety and the life of your vehicle. Think of it like a faulty smoke detector in your house. If the smoke detector doesn’t work and there's no fire, then there’s no big deal. Until there is a fire. This is the same as with your temperature gauge. You have no way of knowing if your engine starts running hot if the gauge is not working. The longer it does run hot, the greater potential for more damage and high repair costs down the road. For a relatively cheap repair cost, you could save yourself a massive bill and a lot of time and aggravation down the road. If your temperature gauge is not working, you really should get it fixed.