Why Is My Temperature Gauge Rising But My Car Not Overheating?

‍Temperature Gauge Rising But Car Not Overheating

If your temperature gauge is rising but the car is not overheating, there are a number of reasons that could be the cause. Let’s look into some of the reasons.

Stuck Thermostat

If the thermostat is stuck in the closed position, this can prevent the cooling system from pushing coolant into the radiator.

This will make your engine coolant hot but not overheating. This will cause the coolant temperature to rise, but the engine may not overheat.

Low Coolant Level

If the coolant level is low in your car, it might be the cause of your engine temperature rising, but not engine overheating.

When there’s not enough coolant in your vehicle, there might not be enough heat absorbing material in your engine to keep the temperature down.

This may be the cause of rising temperature gauges in your vehicle.

Coolant Temperature Sensor

A coolant temp sensor tells you the temperature of your coolant, and relays the information to your vehicle’s computer.

If the sensor has gone bad, there is the potential for the sensor to read that the engine temperature is warmer than it really is.

There can also be a faulty temperature gauge which is connected to the engine coolant  temp sensor.

Electrical Issues

Electrical issues including the wiring up to the coolant temperature sensor, the wiring up to the gauge, and the wiring into and out of the PCM, fuse box, and other junctions can cause the issue of the temperature gauge rising but the car not overheating.

Sometimes a coolant leak onto the temperature sensor can cause the wiring to the sensor to go bad.

Or a faulty water pump can leak onto some wiring causing the wiring to chip away. Electrical issues can be a major concern when you're looking at a faulty temperature sensor.

Faulty Head Gasket

A faulty head gasket can make a car look like its temperature gauge is rising, but the car is not overheating. This is because coolant leaks out to the atmosphere. If enough coolant leaks out, your vehicle will eventually overheat.

How to Test A Coolant Temperature Sensor

To test a coolant temp sensor, you will need a voltmeter. A voltmeter is a device that measures electrical inputs and outputs.

To test your car's voltmeter, first you will have to remove it from the car. To do so, usually you just unbolt the coolant temp sensor from the engine block.

Once you unbolt the temperature sensor from the engine block, place the temp sensor on the table. Hook up the leads of the sensor to the voltmeter.

You want the black lead to go to the right most prong and the red lead to go to the left most prong.

Now switch the multimeter to Ohms (A measure of resistance, not electrical output). Now dip the temperature sensor into some ice water and see what type of readings you get. If your coolant temp sensor is good, you will see a reading of 5 ohms on a reading of 2k ohms on your volt meter.

If your sensor is bad, you will not see an increase in resistance on the voltmeter. This is how you test a coolant temp sensor for your car with a voltmeter.

Here is a great video on how to do it.

Another way to test a coolant sensor is with a scan tool.

If you have a scan tool with the ability to read live data, an even easier way to test would be to get to the temperature reading on the scan tool and check the ECT (see if the temperature shown makes sense with how hot the engine should be).

If it doesn't: check the ECT connector.

When you unplug the connector the temperature on the scan tool should read around -40 F (completely open).

Then jumper the two terminals on the connector (power to ground), this should give you a reading of around 250-284 F.

This completely tests the circuit of the ECT, completely ruling out any electrical issues.

If your two numbers are within the specified ranges: your ECT sensor needs to be replaced since you have a bad coolant temperature sensor. However, if at full open, you have a number significantly more than -40, or at short to power, you have a number significantly less than 250-284: you have an electrical issue.

How To Test For A Blown Head Gasket

Sometimes, the temperature gauge in your car can rise but not cause the car to overheat due to a blown head gasket. The car engine pumps coolant through the engine block up to the engine head.

The engine head and engine block are held together with bolts and a very important gasket that prevents leaks.

When the gasket gets old, it sometimes leaks coolant. When the coolant leaks, it can trick your car into thinking it’s not overheating, since the coolant is being released into the atmosphere instead of boiling.

One way to test for a blown head gasket is to pressure test the cooling system.  To pressure test a cooling system, hook up a pressure tester to the radiator cap of a car or to the coolant reservoir.

First, check to make sure there’s coolant and the coolant reservoir, and that it’s not full of engine oil.

Next, make sure the engine’s temperature is low and there is no coolant flow. You do not want to do this test on a hot engine.

Doing this on a hot engine will possibly lead to burns, so make sure you do not have a hot engine.

Apply pressure to the cooling system. This pressure you just added will test everything in the cooling system from cooling system hoses to an overheated engine.

If your engine holds the pressure, you can be sure that your vehicle does not have a head gasket leak. This may mean to start looking for a broken temperature gauge or a faulty radiator fan, or something along those sorts.

If pressure does start to drop, it means there is a leak somewhere in the engine, and you need to locate it.

The leak may be small, so you will have to pay attention to minor details. But a coolant system flush won’t be enough to fix this issue.

You need to make sure your cooling system operates efficiently before you start driving again, otherwise, you risk overheating the innards of your vehicle which will cause car overheating.