What To Do, Car Overheats and Shuts Off? (Fixed)


No need to panic, we’ll get this sorted out. Car engine overheating is a common problem and most simply require topping up with coolant, but wow there… we’ll need to let it cool first.

engine coolant system

What should you do when your car overheats and shuts off? When your car overheats and shuts off, follow these 8 steps.

  1. Turn on your flashing warning lights
  2. Place warning triangle behind car
  3. Open the car hood
  4. Stand clear of car if possible
  5. Allow engine cool
  6. Remove the coolant cap and top up coolant
  7. Start the car and move to a secure location
  8. Check coolant system for leaks

In this post you’ll learn what to do when your car overheats, how to work safely and get back rolling again asap.

Why Your Vehicle Won’t Start

All modern vehicles are as you know ran by computer and most are programmed to shut off the engine if coolant temperature becomes critically high. It does this for the protection of your engine.

This isn’t the only possible reason you car won’t start but it is the most likely reason.

Your vehicle will likely start again after the coolant temperature decreases sufficiently, but you will need to run a few checks first. See below.

Your Safety Comes First

Obviously your safety is important. If you can limp you car off the road and park in a safe area great, do so. If that’s not possible, take a moment to assess your situation. Is traffic fast moving and visibility poor? Are you stranded on a blind bend? If so, consider moving all passengers and yourself to a safer location.

Ask your passengers to move upstream of the vehicle by a 100 yards or so and to stand clear of the roadside. This way an accidental impact won’t cause debris to fly towards the stranded passengers.

1 Turn On Your Hazard Lights

Your car is equipped with flashing hazard warning lights, they are designed to be used only in case of emergency, this alerts other road users to a potential safety risk ahead. Unfortunately like the boy that cried wolf, hazard lights are used inappropriately and their value has diminished somewhat.

You can find your hazard warning switch usually easily accessed and clearly marked by a red triangle.

2 Place Warning Triangle

If your car has a breakdown kit in the trunk, it may contain a warning triangle. The triangle is designed to be placed about 100 yards to the rear of the stranded vehicle, just off the roads edge. The warning triangle alerts oncoming traffic to the hazard ahead. it’s made from reflective material and some more expensive types are fitted with a flashing light.

When placing the triangle, never take your eye off the moving traffic.

3 Open Car Hood

Engine

Open your car hood, this will help the coolant system and engine cool quickly. If your car is bellowing steam from under the hood, wait for the steam to calm before opening the hood. Use caution, steam will burn your skin on contact.

4 Stand Clear To Rear Of Car

Merc GL

Consider moving yourself and any passengers away from the stranded car. If your car has broken down: at dangerous junction; apex of a corner; brow of a hill; on a fast moving road; visibility is poor; road surface wet or icy etc.

Moving to a position 200 yards or so to the rear of the vehicle while waiting for the engine to cool will help prevent injury should an oncoming car strike your stranded vehicle.

5 Allow Engine Cool

The engine must cool before opening the coolant reservoir, opening it while it is hot will cause coolant to boil instantly and spray from the reservoir cap, scalding you in the process.

Coolant hose

Do not attempt to open the reservoir until the engine has cooled. It will take about twenty to thirty minutes to cool sufficiently. Place your hand on the coolant hose, if it’s warm to the touch but not hot and you can squeeze the hose, it’s OK to open and start topping up.

6 Top Up Coolant

Car coolant

Remove the coolant reservoir cap. The cap will be easy to identify, it’s usually brightly colored or has a yellow warning sticker. A rad and coolant symbol are also common.

The coolant reservoir is a transparent hard plastic tank with an upper coolant level mark and a lower coolant level mark. The reservoir may also carry warning signs and a radiator and coolant symbol.

OK to top up with water?

Yes, topping up with plain water is OK in an emergency. The coolant reservoir tank will likely be well below the low level mark. Ideally we should top up the reservoir to the full mark with coolant, but plain water as you know will do the job too. Now go ahead refit and tighten the reservoir cap.

You should know, consistently topping up the coolant system in this way will dilute the protective qualities of the coolant. Diluted coolant will put your engine at risk of freezing in low temperature conditions, greater risk of boiling in extreme heat conditions and at risk of internal engine corrosion if left in the system for prolonged period.

7 Start & Move Car

Classic Mercedes

As the engine is now cool and topped up with fluid, the engine should restart. Now’s your chance to move the car to a more secure location. Although your car is running, it may have an issue with the coolant system and so may overheat again shortly.

Moving to a secure location now allows you the comfort of at least troubleshooting without the additional stress of an imminent accident.

8 Check For Leaks

engine

With your car safely parked, allow the engine run and open the hood once again. Make the following simple checks:

  • Is the engine temperature gauge reading above normal?
  • Is there steam from the engine?
  • Is the coolant level low again? – Check coolant reservoir without opening the cap, it’s often not easy to see clearly. Bouncing the car up and down helps identify the fluid level.
  • Check under the engine, any sign of leaking coolant?
  • Does the interior heater produce no heat?
  • With the A/C “On”, does the engine coolant fan fail to turn on?

If the answers to the above were no, then all seems fine. Continue on your journey but keep a close eye on your temperature gauge and stop if the temp gets above the normal range.

If on the other hand, some of the answers to the above questions were yes, you’ll need to do a little more diagnoses but driving your vehicle any further. See leaks below.

Leaking fluid?

If you have a leak, try and identify the source and how big the leak is. A large leak is going to prevent you from driving your car, you’ll need a tow truck. Driving with a large coolant leak will at minimum cause a head-gasket to fail and at worst total engine failure. To be sure, continuing to drive the vehicle will cause more damage. Check your auto insurance policy, many auto policy’s cover the cost of a tow truck.

Coolant system info graphic

A small leak will allow you drive home or to a workshop. But it isn’t without risk, you’ll need to key an eagle eye on the temperature gauge and stop, allow the engine to cool and top up, before continuing on your journey.

Common coolant system leaks:

  • Pipe fittings – Check hoses for splits and loose or faulty clamps.
  • Water Pump – Check for a leak at the water-pump, or high pitched squeal.
  • Radiator – Check the rad for damp patches.
  • Radiator cap – Check for staining around the rad cap area, indicates a worn cap seal.
  • Heater core – Check carpet in front passenger area for dampness and a sweet smell.

Common Causes Of Overheating Coolant System

Car Thermostat
Coolant System Thermostat

I’ve been a mechanic for over twenty years and here’s a list of the most common causes of an overheating engine. Some are really simple inexpensive repairs that could easily be nailed by the owner, and some are definitely a job for a trained mechanic.

I’ve listed all the easy to solve, low hanging fruit first.

  • Low coolant level
  • Bad radiator cap
  • Leaking hose clamp
  • Leaking hose
  • Loose/broken drive belt
  • Faulty thermostat
  • Blown radiator radiator fan fuse
  • Air locked coolant system
  • Faulty radiator fan
  • Split radiator
  • Blocked radiator
  • Split reservoir tank
  • Head gasket failure

Why does a car lose power when it overheats?

A car will commonly lose power when it overheats simply because the cylinder head expands and allows cylinder compression to escape past the cylinder head gasket. This often also causes a no start after the engine overheats. It’s a serious condition and can cause damage to the head-gasket or warping of the cylinder head.

Head gasket failure chart

The cylinder head gasket is as you may know, a graphite material that’s sandwiched between the top and bottom halves of the engine. It’s function is to seal the combustion chambers and keep oil and coolant separated.

A leak-down test or a exhaust chemical analyses kit are the two most common tests for a suspected head-gasket fault.

Engine leak down infographic

Related Questions

How long should I wait to start my car after overheating? Wait 20 minutes with the hood up, this helps cool the engine quickly.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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