If you’ve arrived at this page while standing on a highway shoulder while traffic roars past, I’m sorry.
How To Identify an Overheating Engine?
You may notice steam exiting from from under the hood. Perhaps the dashboard temperature gauge spiked into dangerous high-temperature territory. Often, a sweet, syrupy smell of engine coolant is common with an overheating engine. In some cases, the coolant will even boil.
It happened to me years ago while road tripping across the country. I pulled into a rest stop along the Interstate on a blazing-hot day, shut off the engine and thought, “What’s that bubbling sound?” The coolant was literally boiling in the overflow tank.
Video transcript: Keeping Your Engine Cool
Featuring John Gardner, ASE Master Certified technician, automotive technology instructor and host of Motorhead Garage, with AMSOIL Director of Product Marketing Len Groom (author profile).
John Gardner: These fans are great for keeping us cool, but how does a fan keep an engine cool? Welcome to this AMSOIL tech tip. Yep. It’s all about the law of thermodynamics.
Let’s talk about coolant fans. What’s happening? Well, we’re taking heat from hot places and transferring it to a place with less heat. The engine, boom, fires inside, the coolant carries it outside, and we get rid of it.
That’s exactly what’s going on. Hot to less heat. The radiator is dissipating it to the outside atmosphere. Now, can see right here, there’s two types of fans.
You have a silicone driven fan or you can have an electric coolant fan. I have them both sitting right here. Now, a silicone driven fan or a viscous fan here, you can see it. That’s usually the big fan blades on the front of the car and that engages at different times when the engine gets hot or cold.
The little bimetallic spring kind of tightens it up and gives you that coolant effect. Now, most cars today, well, they have electric coolant fans like this one. If you have an electric coolant fan, well, it turns on at different times. You can see the schematic right here and it’s actually driven by the computer.
The engine control module then hits a relay and turns it on. When does it turn it on? Usually when you do the air conditioning or when it gets hot. You know, they usually take twelve volts and it’s pretty easy to test.
You can just take a voltmeter, you can go down to your fan to your positive and negative wire, either turn your air conditioning on or wait for your car to actually engage it. Once you engage that coolant fan, you should see twelve volts on that wire. I’m turning it on now. You’re seeing it run.
You should have twelve volts there. If you don’t, you just have to trace it back in the schematic. A good diagnostic for you. See by the graphic here that most cars have water jackets, but today on motorcycles, v twins, all kinds of stuff, use fin cooled engines still.
Man, that creates a lot of heat and heat’s not our friend.
Len Groom: No. Not in this situation. Heat can be bad, especially when the oil is involved.
You see this on like large Harley-Davidson* bikes. You see guys in Sturgis pushing their bikes along the side of the road. Typically, what happens there is the oil gets so hot. All oils are gonna naturally thin out as they get warm.
It means your oil pressure starts to drop. So the key to survival in that situation is start with really good building blocks. So what we do is we make sure that the oil maintains its viscosity under high high temperatures. Three hundred degrees is not uncommon on some of those big V twin bikes.
So you maintain the oil pressure, keep the oil moving. Once it’s moving, that’s critical. It can lubricate and it doesn’t oxidize and it doesn’t tend to stick to the different parts. So good building blocks really takes you a long ways.
John Gardner: Now my son drives a Harley, so I know from experience. The V twin community, they believe in AMSOIL, man. That’s all they use. And why do they do it?
Well, number one, it’s the best. And number two, you got this whole kit right here, man. Everything. You got the oil filter.
You got the o ring. Everything you need to do in an oil change in one kit. Check it out for yourself at AMSOIL.com.
Low coolant and insufficient airflow are two common causes of an overheating engine.
What To Do if Your Engine is Overheating?
1) Turn up the heat
It may sound counterintuitive on a sweltering summer day, but if the ambient temperature is too high, and airflow is inadequate, your vehicle’s cabin heater can help draw heat away and cool the engine. Be sure to open your windows!
2) Stop driving
Pull over and shut off the engine, preferably in a shady spot, to allow the engine to cool naturally.
3) Check the coolant level
After the engine has cooled, pop the hood and verify the coolant level is at the “full” mark on the coolant reservoir. If the coolant overflow level doesn’t reach the bottom of the filler neck, low coolant could be why your car is overheating.
4) Add coolant if needed
Hopefully, you have a gallon of coolant in your vehicle. Make sure the engine has cooled first or you may burn yourself. If your vehicle requires adding coolant directly in the radiator, slowly remove the radiator cap with a rag or towel to prevent scalding-hot coolant or gasses from touching your skin.
5) Walk or drive for help
If you don’t have coolant, walk to the closest service station or auto parts store while the car cools down. If it’s too far to walk, once the engine has cooled, it may be possible to drive to a service station very slowly and at low rpm, while suppressing engine temperature as much as possible.
6) The backup plan
If you cannot operate the vehicle or repair it yourself, it’s time to call whichever friend owes you a favor, or call for roadside assistance. In extreme emergencies, flag down a passing motorist for help.
A bad thermostat can prevent coolant from flowing, causing the engine to overheat.
What Causes an Engine to Overheat?
1) Low coolant level
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
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 sensor switch
The temperature-sensor switch that turns on the fan may 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
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 replace it than try to troubleshoot it. The same applies to a faulty radiator cap.
5) Plugged radiator
Check externally for leaves, bugs and other debris plugging the fins and blocking airflow. One trick is to shine a flashlight through the radiator from under the hood then look through the vehicle’s grill. If you can’t see the light, the radiator needs cleaning.
A radiator can also be internally clogged and cause your engine to overheat. Plugged coolant passages will likely lead to a failed radiator. Using low-quality coolant or neglecting to service the cooling system can cause it to become plugged with sludge or corrosion.
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. Flush the system, replace the radiator and refill with a high-quality coolant.
6) Busted hose
Many cooling systems move hot coolant through rubber hoses, which deteriorate with time and temperature. A coolant hose rupture can leave your vehicle inoperable. Fortunately, hoses are relatively inexpensive to replace. Unfortunately, they are often challenging to repair on the side of the road.
Bad coolant can cause sludge and corrosion that plugs the radiator, causing your car to overheat.
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David Hilgendorf is an AMSOIL Technical Writer who develops content for automotive, powersports and industrial audiences. His work includes technical data sheets, magazine articles, blog posts, white papers, product literature and application guidance. Hilgendorf works with engineers, laboratory personnel and technical specialists to communicate lubricant testing, product performance, maintenance practices, metalworking fluids, grease, motorcycles, marine equipment and industrial reliability.
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