Close

Car Temperature Gauge: What to Do if It's Too Hot, Too Cold or Broken

Stephen Fogel
May 7, 2018

temperature gauge

The temperature gauge on your dashboard is an important indicator of your engine’s running condition. It can provide you with an early warning of a potential problem — and on rare occasions, it can even malfunction. 

What to do if your temperature gauge reads hot

If your temperature gauge is reading hot, this is very serious. Your engine is likely overheating — which can create expensive consequences if you don’t deal with it immediately. You may also see a red warning light or hear a warning chime when this happens.

Pull off the road as soon as you safely can, and shut off your engine. Don’t open the hood and investigate — you could get badly burned. Call your mechanic and explain the problem. A tow truck will likely be the next step, since your vehicle may not in drivable condition. Avoiding any further damage should be your first priority. 

What is causing the overheating? It could be one of the following causes, or possibly a combination of factors:

  • Loss of coolant
  • Water pump failure
  • Bad thermostat (stuck in closed position)
  • Clogged radiator
  • Collapsed radiator hoses
  • Electric cooling fan failure
  • Drive belt failure (if fan is engine-driven)
  • Head gasket failure 

Whatever the cause, this isn’t something you can put off. If you catch it quickly enough, there may be no lasting damage to your engine, and you can continue driving it after the cooling system repairs are made. If it’s the head gasket, your mechanic can provide you with a list of options.

Get it diagnosed by a professional
 

What to do if your temperature gauge reads cold

If you haven’t driven your car for a few hours, it’s normal for your temperature gauge to read cold for a few minutes after you start it. It may take a bit longer to move off the cold position during extreme winter weather. But if your temperature gauge continues to read cold after you’ve been driving for a while, something else is going on.

While a steady cold reading is nowhere near as drastic a situation as a hot reading, it’s still a sign that you have a problem. The cause of this is likely to be one of two things:

  • Bad thermostat (stuck in open position)
  • Bad temperature gauge

If the thermostat is stuck open, and it’s the dead of winter, your vehicle may be unable to produce enough heat for defrosting and heating purposes. This can be dangerous if you get stranded somewhere. Have your mechanic take a look at the thermostat.

» MORE: Get an estimate for your car repair

How should your temperature gauge normally read?

When everything is working properly, your temperature gauge should read somewhere in the middle of its range, between the cold and hot markings at the ends of the scale. The exact “normal” spot can vary from vehicle to vehicle, but as long as it’s more or less in the center, all is well.

Your temperature gauge may occasionally read slightly higher than normal. This can happen if you’re doing a lot of stop-and-go driving in a very hot climate, carrying a full load or towing something, and you have the air conditioning on full blast. As long as you don’t get too close to the hot end of the scale, it shouldn’t be a problem.

If the temperature gauge keeps rising and looks like it is approaching the hot mark, here are a few things you can do to keep your vehicle from overheating:

  • Turn off the air conditioning 
  • Turn on the heater
  • Pull off the road for a while and shut off your vehicle
  • Let your vehicle cool down for an hour or so, and add coolant if necessary (only through the reservoir, never by removing the radiator cap

How your temperature gauge works

The gauge measures the temperature of your engine’s coolant. As the primary means of regulating how hot your engine gets, your coolant circulates through the engine, absorbing the heat produced by the combustion in the cylinders. It then releases that heat to the atmosphere as it travels through the radiator.

Your temperature gauge uses a sensor that is exposed to the coolant flow. This sensor is usually located near or in the thermostat housing and sends an electrical signal that corresponds to the temperature reading. This signal travels to the temperature gauge on your dash, where it’s converted into a reading of the current coolant temperature.

Most vehicles made since 1996 instead send this signal to the engine computer. This unit processes the temperature reading and passes it on to the gauge in your dashboard. This means that your temperature gauge is also a part of your emissions control system, and can affect that aspect of your vehicle’s operation.

How to identify and fix a bad temperature gauge

Temperature gauges are normally very reliable. An abnormal reading usually indicates a temperature-related problem in your engine, not a bad gauge. But it is possible for the gauge to malfunction.

If your temperature gauge moves around erratically, or has given you an extreme reading when there are no other symptoms or problems under the hood, then it may be busted.  

The source of your temperature gauge-related problem can be one or more of the following:

  • Bad coolant temperature switch
  • Bad wiring
  • Bad connectors
  • Bad temperature gauge mechanism
  • Problem in the engine computer
  • Loose radiator cap

You can try replacing the radiator cap, if you think it’s the problem. It’s an inexpensive part and easy to do — just make sure the engine is off and cold when you do it. But it’s best to let your mechanic investigate the other causes.

Because your coolant temperature sensor also sends information to your engine computer, a bad sensor can cause the following additional symptoms: 

An emissions system-related problem is very likely to trigger a trouble code, which your mechanic can interpret with a code reader. This usually points to the source of the problem, which can then be fixed.

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

No comments yet...

Sign in to comment

Related Questions

See what others have asked about this, or visit the Questions page to ask your own question.
Whilst driving round town my temperature guage and heaters work fine but when on a run on the motorway the temperatur...
This problem started about two months ago. when you start the car, the temp gauge goes to about 1/2 between hot and ...