Temp gauge goes up and down

The temp gauge goes up to ninety then goes back down

My car has 176000 miles.
My car has a manual transmission.

Experienced mechanics share their insights in answering this question :
Hi There,
This can be caused by a number of things such as a faulty thermostat, a clogged radiator or potentially a faulty cooling fan relay. The thermostat regulates the flow of the coolant in your car’s engine and controls when the coolant flows in and out of the motor from the radiator by opening and closing at specific temperatures. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. When the thermostat is stuck open it can cause the coolant to circulate constantly resulting in the motor never reaching the correct operating temperature.

The typical electric cooling fan circuit includes a temperature sensor, a relay, a control module and the fan motor. The relay is the component that fails most often, so be sure to test the relay as well as its power supply and ground connections. A good relay coil will typically read 40 to 80 ohms. If resistance is high, the coil may still be working but it is failing, or it may not work when electrical loads are high. If the coil has no resistance, it is open and has failed and you will need to replace the relay. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your cooling system.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

One common cause is a defective thermostat, a component that is inexpensive and easy to replace. Other causes of a fluctuating temperature gauge are a failing radiator fan, insufficient coolant level and a leaking cylinder head gasket. A failing radiator fan will be erratic.
If your engine begins to overheat only when you`re idling, but the needle on the temperature gauge begins to move down once you pick up speed, the most likely cause is that something is wrong with the radiator fan. As you drive, air will flow over the radiator, which helps the coolant get cool again.
It gets even more concerning and confusing when car overheating suddenly returns to normal. This phenomenon can happen for many reasons, like a bad thermostat, a faulty radiator, or a coolant leak. As such, it`s best to get your car checked by a professional— like RepairSmith!
Engine Overheating

A failing water pump will cause your engine to heat up, and that`s not a good thing. To prevent catastrophic engine failure, look for these signs of an overheated engine due to water pump failure, including: A fluctuating temperature gauge.

Frequent fault symptoms are: Higher idle speed. Increased fuel consumption. Poor starting behaviour.
Why is my car overheating but it has coolant in it? It could be that the coolant concentration is not correct, or you may have a bad thermostat, a failed water pump, broken drive belt, or a bad radiator or radiator fan.
Normal body temperature is considered to be 37°C (98.6°F); however, a wide variation is seen. Among normal individuals, mean daily temperature can differ by 0.5°C (0.9°F), and daily variations can be as much as 0.25 to 0.5°C.
First of all, driving an overheated car can do more damage and make the problem worse. And secondly, even if your car does eventually cool down, it`s not necessarily safe to drive it. So, if your car ever does overheat, it`s best to pull over and call for a tow truck.
Differences between measurements can also result from the following factors: The thermometer is not the same temperature as the room you are measuring in (Example: it has been in a much warmer or colder room). The thermometer is inserted into the ear canal at a different depth or angle.
Fluctuations are due to changes in hormonal activity over the course of the day, your environment, and physical activity. For instance, you may have a lower temperature in the morning after sleeping in a cold room, and a higher temperature after exercising or doing housework.
Fluctuating body temperatures are a normal part of the human body; however, there is a difference between a warmer body temperature at certain parts of the day and having a consistent fever.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Temperature gauge does not work – 1998 Mercury Grand Marquis
ANSWER : You will need to test the computer to scan for data of the temperature sensor to see if the computer is reading the correct temperature as tested externally on the coolant sensor. If the sensor is not accurate then replace the sender. If the sender is accurate then you will need to have the temperature gauge replaced.

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changed thermostat and radiator, temp gauge goes to hot when sitting still mostly, then goes back down to normal temp. Happens eve
ANSWER : Hi there. If you did not properly bleed the cooling system after completing these repairs, it’s more than likely that you have air bubbles inside the coolant system causing this problem. However, it could also be due to a bad electrical harness or connection to the thermostat or temp sensor on top of the radiator as well. It’s probably a good idea to have a professional mobile mechanic come to your location and complete a car is running hotter than normal inspection, so they can pinpoint the source of this issue and recommend the right repairs.

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This is Luis from Mesa, AZ. I have a 2000 Maxima. Temp gauge rises when coolant level is normal, but when level drops, gauge reads
ANSWER : Hello Luis, thank you for writing in. If the vehicle is leaking coolant, and you are seeing white smoke or steam from the exhaust, then your engine is consuming the coolant. This happens when your head gasket allows coolant to flow into the combustion chambers. It is also why you are likely only loosing coolant when you drive. At this point, do not worry about the other symptoms. Most of them may rule themselves out when the head gasket is repaired. If there has been any further damaged to the cooling system, we can sort them out after the leak is taken care of. Keep in mind the coolant overflow tank needs room in it in case the cooling system heats up and the coolant expands, it needs a place to drain into so you do not loose that coolant. For more help replacing the head gasket, contact our service department to schedule an appointment.

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If the temp gauge don’t go beyond the halfway point do I have a bad radiator? No coolant on grounds noted.
ANSWER : Hey there, thanks for writing in about your Toyota Sienna. You could have a leaking radiator without knowing it. I was taught that there are classes of leaks; class 1 is a leak that just leaves a wet spot on the part, class 2 is where the drop forms but doesn’t drip, class 3 is where is leak drips on the ground. They may not have been 100% honest about how serious it was but it may have been a leak.

Will it stay at the lowest point? No, your car has an operating temperature of around 150-160 degrees fahrenheit. Depending on where you live and what state it could be lower or higher. I cannot speak on the reasonable part because it depends on where you live and the price the shop charges by the hour. Good luck and I hope this helps.

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heater doesnt blow hot until over 2500 rpm, and in cold weather temp gauge goes all the way to hot indicating overheating.
ANSWER : Hi there. In most cases when this issue occurs, it is due to an obstruction inside the heater core. The coolant system flows through the heater core to supply heat. Over time, the heater core will develop sludge and debris that will solidify inside the core. As engine RPM increases, the coolant flows faster, which can break loose the heater core obstruction. However, it’s also possible that this issue is related to an electrical fault. I would recommend having a professional mobile mechanic come to your location and complete a heater is not working inspection so they can determine what is causing your problem.

Read Full Q/A … : Temp gauge goes up and down

Temp gauge goes up and down
ANSWER : Hi There,
This can be caused by a number of things such as a faulty thermostat, a clogged radiator or potentially a faulty cooling fan relay. The thermostat regulates the flow of the coolant in your car’s engine and controls when the coolant flows in and out of the motor from the radiator by opening and closing at specific temperatures. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. When the thermostat is stuck open it can cause the coolant to circulate constantly resulting in the motor never reaching the correct operating temperature.

The typical electric cooling fan circuit includes a temperature sensor, a relay, a control module and the fan motor. The relay is the component that fails most often, so be sure to test the relay as well as its power supply and ground connections. A good relay coil will typically read 40 to 80 ohms. If resistance is high, the coil may still be working but it is failing, or it may not work when electrical loads are high. If the coil has no resistance, it is open and has failed and you will need to replace the relay. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your cooling system.

Read Full Q/A … : Temp gauge goes up and down

Fuel gauge and temperature gauge not working.
ANSWER : The fuel gauge not reading properly may be likely related to your fuel sending unit or the gauge in the dash itself. The sending unit is a small float type component inside your fuel tank that measures the level of the fuel inside the tank. As the fuel level drops, the float level changes and sends a signal to the car’s computer which then displays the reading on the fuel gauge in your dash.

The temperature gauge also has a sensor (or in some cases called a switch) that reads the coolant temperature and relays this information to the ECU which uses this information to control other functions such as the air/fuel ratio during warm up. This also serves to control the turning on and off of the cooling fans when the temperature reaches a specific threshold. When this is not working properly, you may also experience the engine overheating in some cases. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your gauges.

Read Full Q/A … : Temp gauge goes up and down

Temp gauge goes up and down
ANSWER : Hi there. The temperature sensor is the device used to determine the estimated engine coolant temperature reading. The sensor itself is not always perfect. This device sends a signal to the computer and in some cases, the instrument cluster as well. A loose connection or malfunctioning sensor can sway the values and show an improper reading. If you need further assistance, I recommend you have a certified technician, like one from YourMechanic, inspect the electrical components to make sure all the connections are good and replace any failing parts

Read Full Q/A … : Temp gauge goes up and down