Car Engine

Why My Engine Is Hot And The AC Is Turned Off?

Mike Cross
Updated Oct 6, 2021

Your engine is one of the most vital elements of your vehicle. When it gets hot, that can spell a whole lot of trouble. Not to mention, overheating is one of the top causes of death for a vehicle’s engine. In fact, your vehicle will give off a warning saying “Engine Hot, AC Off”.

It is important to ensure that your engine stays alive for as long as possible and will not die a horrible early death due to overheating. There are some situations when the engine is hot and your AC system is off at the same time. We’ll dig into some potential causes to what may cause your engine to get hot even when the AC is not in use.

engine hot ac turned off
What Is Happening When The Engine Is Hot And The AC Is Turned Off?

Potential Issues When The Engine Is Hot And The AC Is Turned Off

An overheating engine can be caused by a vast majority of issues. If you are not mechanically inclined, a mechanic will only be able to make some determinations and rule out any other issues while looking at your vehicle. With that in mind, let’s take a look at what might be going on under the hood:

Coolant Levels:

Pouring antifreeze liquid screen wash into dirty car
Pouring antifreeze liquid screen wash into dirty car

One of the common issues that you may run into is a low level of coolant. If the level of coolant is low, then it’s time for a refill. You’ll need to add coolant to the reservoir (not the radiator) to ensure that it will be enough to cool off your engine when the situation warrants it. Before adding coolant, you’ll need to consult the vehicle’s owner’s manual. You’ll need to know the appropriate coolant that is suitable for your engine. Different engines mean different types of coolant.

Once you find the coolant that is suitable for your vehicle, pour in the appropriate amount in your reservoir. Keep in mind that while you’re doing this, you should keep your hands and clothing away from your engine’s cooling fans. Even when the engine is off, the fans still can kick on. Be sure to fill the reservoir to the cold engine line if the temperature is just that (cold). You are free to use a diluted version of coolant, which consist of 50 percent coolant and 50 percent water.

Blown Head Gasket:

An overheated engine is a critical symptom to a major problem. In this situation, it is a blown head gasket. The purpose of a head gasket is the seal between your vehicle’s engine block and the cylinder head. More specifically, it is to seal off the hot gases and the engine coolant. The head gasket itself isn’t visible when the engine is assembled. The only time you’ll ever see it is when you have to take the engine apart. It is for this reason that head gasket issues are usually hard to diagnose. And it would most likely need to be looked at by a mechanic to ensure that a head gasket may be the cause of your engine overheating.

A visual inspection may not confirm if you’re having head gasket issues. That’s why you’ll need to find out any secondary symptoms your car or its engine may be suffering prior to having it looked at for a possible broken head gasket. The following are some symptoms to look out for if you believe your head gasket is broken:

  • A discharge of white, milk-like oil.
  • Engine is overheating.
  • Integrity of cooling system is low.
  • Coolant leakage, more specifically from below the exhaust manifold.
  • Bubbles are visible in the vehicle’s radiator or overflow tank.
  • White exhaust smoke.
  • Bad spark plugs.

These are the symptoms to look out for aside from just assuming if a head gasket is blown. It may be something else, so check your vehicle for these secondary issues before having a mechanic look at it. If you’re not mechanically inclined, the mechanic will look for these symptoms before making a determination.

Malfunctioning Temperature Sensor:

Whether you know it or not, a temperature sensor is vital to your engine. When it malfunctions, this can spell disaster for your engine. It is common for an engine to run hot without causing the coolant in your radiator to boil or damaging the components. While an overheating engine is perhaps one of the major symptoms that are associated with a malfunctioning temperature sensor, there are some secondary symptoms to look out for to determine if this is causing your engine issues. They are as follows:

  • Check Engine Light: A no brainer here. The computer in your engine will pick up on issues that will have to do with the temperature sensor. This will also include issues regarding the circuits associated with the sensor. Click anything to know about check engine light to learn more.
  • Stalling Engine: If you’re engine hesitates or stalls upon start up, then there’s a good chance your temperature sensor may have a problem. More specifically, a faulty sensor will often throw off your engine’s computer and prevent it from providing enough fuel for the engine to turn over.
  • Engine Overheating: As mentioned, this is one of the major symptoms of these issue. More specifically, your engine’s computer will not get a proper reading. Because of this, it won’t be able to slow down the ignition and allow the cooling fans to turn on. If this happens, the engine will begin to overheat. At that point, you’ll need to shut off the vehicle immediately. If you are driving, pull over to the side of the road (where it is safe).


Knowing these three common issues to the “Engine Hot, AC Off” warning is key. It is important to take this to a mechanic as soon as possible to diagnose what is actually the cause of this happening. Remember to take note of the secondary symptoms that are associated with potential issues like low coolant or a blown head gasket. Neglecting to take care of your vehicle’s engine when it overheats will kill your vehicle, rendering it useless. If you believe that your engine is overheating, do not wait any longer. Pull over to the side of the road and call for help if you’re on the road.

Mike Cross
Life is too short to drive with stock audio

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