Why is My Engine Overheating?

If your car is overheating, pull over and let it cool before checking the coolant level.

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AMSOIL Antifreeze & Coolant
author John Baker
by John Baker
June 23, 2020

If you’ve arrived at this page after having angrily asked Siri or Google “Why is my engine overheating” while semis fly past on the highway at 75 mph (120 km/h), I’m sorry.

How To Know If Your Engine Is Overheating

You may have noticed steam boiling out from under the hood. Or, maybe, the coolant/water-temperature gauge spiked into dangerous territory. The sweet, syrupy smell of engine coolant is also common with an overheating engine.

In some cases, the water/coolant can boil.

That’s what happened to me years ago while driving my Oldsmobile Delta 88 across the country. I pulled into a rest stop along Interstate 70 in Kansas on a blazing-hot day, shut off the engine and thought, “What’s that sound?” The coolant was literally boiling in the overflow tank.

Why Is My Engine Overheating? Here’s What To Do

Time needed: 30 minutes.

Steps to take if your engine is overheating

  1. Stop driving

    If you’re driving, pull over and park in a shady spot if possible. Shut off the engine.

  2. Let the engine cool

    Don’t immediately pop the hood. And don’t immediately remove the radiator cap. Instead, let the vehicle sit for several minutes to cool down.

  3. Check coolant level

    Once the engine is cool, you’re safe to check the coolant level.

    Check that the coolant level is at the “full” mark on the coolant reservoir. If your vehicle requires you to add coolant directly in the radiator, remove the radiator cap using a rag. Again, make sure the engine is cool first or you may burn yourself with scalding-hot coolant.

  4. Add coolant, if needed

    Does the coolant level reach the bottom of the filler neck? If not, that could be why your car is overheating. Hopefully, you have a gallon of coolant in the trunk or behind the seat of your truck. If not, it’s time to call whichever friend owes you a favor.

  5. Carefully drive to a parts store, if you can

    If you’re near a parts store or other retailer that sells coolant, you’re probably safe to start the vehicle after it has cooled and drive slowly and methodically to the store to buy coolant. Take it easy, though, to suppress engine temperature as much as possible.

  6. Call for a tow, if needed

    If you have no coolant on hand and can’t obtain some, call for a tow.

Why Is My Car Overheating?

It could be due to several reasons.

1) Low coolant level

As said, low coolant level is the first potential cause to investigate. Look for coolant leaks on the ground under the radiator and engine. Better yet, have a mechanic pressure test the system. Check the oil level to ensure coolant isn’t leaking into the engine. Fix any leaks you find.

2) Bad cooling fan

A bad cooling fan is another potential cause. Start the vehicle and crank the air conditioning. Check under the hood to ensure the cooling fans are spinning. A bad fan won’t pull sufficient air across the radiator to cool the engine. Check the fuse first. If it’s fine, the motor may be burned out or the thermostatic switch may have failed.

3) Faulty temp-sensor switch

The temperature-sensor switch that turns on the fan may also have failed, as could the cooling-fan relay. Unless you’re handy with a multimeter, it’s best to have a mechanic test for these problems.

4) Bad thermostat

A faulty thermostat is another prime culprit. The thermostat should close until the engine warms and then open after it’s hot to allow coolant to flow through the system. If it sticks shut, coolant can’t flow, increasing engine heat. If the engine is warm, but the upper radiator hose is cool to the touch, it could mean the thermostat is bad.

A thermostat is so inexpensive that it’s often easier to simply replace it than try to troubleshoot it. The same applies to a faulty radiator cap.

5) Plugged radiator

A radiator plugged with sludge or corrosion can also cause your engine to overheat. It may look fine on the outside while the inside is a mess. Then again, it may not look fine on the outside. Check for leaves, grasshoppers and other junk plugging the fins and blocking airflow.

One trick is to shine a flashlight through the radiator from under the hood. Look through the vehicle’s grill. If you can’t see the light, the radiator needs cleaning.

Plugged coolant passages will likely accompany a bad radiator. Using a low-quality conventional coolant or failing to service the cooling system can cause sludge or corrosion to build up in the system. Just like your arteries need to be clean to flow blood through your body, the radiator and cooling passages must be clean to properly flow coolant. If not, the engine can overheat.

In this case, flush the system, replace the radiator and refill with a high-quality coolant.

Use a good antifreeze & coolant

AMSOIL Passenger Car & Light Truck Antifreeze & Coolant is a perfect option. It eliminates additive drop-out, scaling and other issues inherent to conventional “green” coolants. It’s pre-mixed 50/50 with high-quality water and lasts up to 150,000 miles or 5 years.

And, as the image shows, it fights corrosion, maximizing the life of your cooling system and helping prevent your engine from overheating.

AMSOIL Antifreeze and Coolant prevents corrosion


by John Baker

AMSOIL Technical Writer and 12-year veteran of the synthetic lubricants industry. Enjoy making complex topics in the automotive, powersports, industrial and other markets understandable. Avid DIYer who always seeks to repair rather than replace.

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