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WTF!? My Car Temperature Gauge Goes Up and Down While Driving.

Fact: Everyone’s car temperature gauge goes up and down while driving. 

When you start your car, your coolant is cool. 

As you drive, your coolant warms up and  your temperature gauge will rise.

Go ahead and say it…. DUH!  I know this is common sense…. But I’m just trying to be clear with y’all.

What this article is about is when your temperature gauge dances around erratically while you are driving. If this is happening to you, this article will give you some suggestions on what might be causing the problem and what you can do to fix it.

What sucks is that when your car temperature gauge goes up and down while driving, it’s not all that easy to pinpoint the reason it’s happening. There are several possible reasons and you might need to use a little trial and error to fix the problem. So let’s get to it.

Reasons your car temperature gauge goes up and down while driving

Bad Thermostat

In case you didn’t know, your engine has a cooling system. And guess what it does? It keeps your engine cool! 

The system uses fluid called coolant (AKA antifreeze) to flow around the engine and keep it cool while it runs. 

Your thermostat is a valve in this system that opens and closes depending on the temperature of your engine. When the engine gets hot, the thermostat opens and starts sending fluid to your car’s radiator to cool down and then flow back to the engine.

When the thermostat starts to fail, it can open and close erratically or get stuck open or closed. This can cause your car temperature gauge to go up and down while driving.

Replacing a thermostat is a fairly easy job and can be done by a novice DIY mechanic. 

Bad coolant temperature sensor

As the name implies, the coolant temperature sensor monitors the temperature of your coolant and sends the data to your car’s engine control module (ECM). The ECM then uses the data in a variety of ways including how rich to make your fuel mixture and sending data to your dashboard temperature gauge.  

That said, if this part fails, it can cause your car temperature gauge to go up and down. 

The good news with this is that if your coolant temperature sensor is failing, it’s also likely to trigger your check engine light and you’ll know right away that a bad coolant temperature sensor is your problem.

The other “good” thing about a falling coolant temperature sensor is that it is an easy part to replace and even the most novice DIY’er can replace it.

Water pump issues

Your water pump is a part that circulates coolant through your engine. If it starts to have problems, it can be the source of why your car temperature gauge goes up and down while driving.

Possible reasons why you have water pump issues can include: the belt driving your water pump is too loose, or maybe an internal part on the water pump (like the impeller) is failing.  

Whatever the reason, an issue with your water pump can cause your temperature gauge to go up and down while driving.

While not as easy to replace as a thermostat or a coolant temperature sensor, replacing a water pump is a fairly easy job and can be done at home if you are confident. And it won’t be super expensive if your mechanic of choice replaces it for you.

System short

In most modern cars, information about the temperature of your car’s coolant is sent to the temperature gauge via wires.

The coolant temperature sensor monitors the temperature of the coolant. It then sends the information to your car’s ECM. And then your ECM sends the data to your temperature gauge so you can see it.

All this magic takes place through a series of wires and electrical signals. If one of the wires experiences a short, it can cause the system to become glitchy and make your car temperature gauge dance.

Shorts are often inexpensive fixes, but it can take time to locate them.

Bad temperature gauge

The first thing a lot of people assume when their car temperature gauge goes up and down while driving is that the gauge itself might be broken. This is highly unlikely.

A broken temperature gauge is a fairly uncommon problem. Temperature gauges tend to last the lifetime of a car.

If your car does have a bad temperature gauge, it most likely won’t work at all. The gauge will probably just stay in the cold zone without moving. 

A word on overheating

Because we’re on the topic of a car temperature gauge that goes up and down while driving, it makes sense to touch on overheating.


When your car is overheating, the gauge will not be going up and down. It will go up and stay up in the hot range. 

You need to take this seriously! Overheating is no joke. And if it’s not properly dealt with, you could cause a lot of very expensive damage to your engine. For more information about overheating, check out this post on the Napa Know How blog.

Conclusion

If your car temperature gauge goes up and down while driving, you could be experiencing any one of several problems that aren’t easy to pinpoint. It may take some trial and error to find the cause of the temperature gauge going up and down. Don’t delay putting it off because your temperature gauge gives you important information about the health of your car’s motor. And without it, you risk damaging your car. 

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