Engines run using highly flammable fuel and sparks. They complete thousands of revolutions per minute, so it’s no surprise they get hot.
But how hot? And how long does it take cars to cool down?
The wise guy’s answer would be to say that it depends on how hot the car was in the first place.
However, 30 minutes is generally enough time for a car to cool down.
This guide will address several situations you might have found yourself in.
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Why Does An Engine Get Hot?
An engine works by mixing gasoline (or diesel) with air – that is, oxygen. It sucks this mixture into a small space: the combustion chamber.
Here, a spark plug fires, igniting the air/fuel mixture. This drives a piston downwards and, via the connecting rods, creates a rotational force in the crankshaft.
This rotational force drives the wheels.
Imagine how hot a campfire or fireplace gets right in the center. Your engine is – more or less – doing precisely the same thing, but in a controlled manner.
The heat is absorbed by the block of metal surrounding these pistons and cylinders (the engine block). The coolant (and, to a lesser extent, the oil) removes this heat and distributes it to the atmosphere.
How Long Does It Take For An Engine To Cool Down?
If you’ve run the car at operating temperature (between 90 and 100 degrees C for most vehicles), it’ll take about 30 minutes for the engine to cool.
It might still feel warm to the touch. When mechanics and engineers say “cool, ” they usually refer to a safe temperature for working with the engine.
If you want to ensure the engine’s cold, you should wait several hours. Overnight is the best bet – the sun won’t be warming things up.
How Long Do You Have To Wait To Change The Oil?
When a mechanic conducts an oil change, they want the oil to be warm. That’s because hotter liquids have a lower viscosity than when they’re cool. In other words, they’re thinner.
From a purely scientific standpoint, the hotter the oil, the better. Technicians could do an oil change with the engine still at operating temperature.
They don’t, though. Why? Because of burns. When removing the oil drain plug, some of the oil will inevitably get on their hands or clothes.
Hot oil is incredibly dangerous. For that reason, they’ll usually wait a little while before changing your oil.
It won’t usually be more than 30 minutes.
Note: mechanics shouldn’t change hot oil for safety reasons. However, inevitable pressures from time and management might mean they get on with it anyway.
If mechanics need to do a cold oil change, they’ll run the engine for a couple of minutes first. This warms it up to improve the flow – but it’s far from ‘hot.’
How Long Do You Have To Wait To Check The Coolant?
Checking the coolant is another vital part of car maintenance. You should wait at least 30 minutes after you last drove the car, just to be safe.
You don’t need to remove the reservoir bottle cap or radiator cap to check the coolant level. Look through the clear plastic container or use the dipstick if your car has one.
If you want to check the condition of the liquid itself, you will need to remove the cap.
Be very careful. The coolant system is pressurized. When it’s hot, the fluid expands. When you unscrew the cap, all this excess pressure will shoot past your hand, and the steam will scald or burn you.
It doesn’t sound like much, but the injuries can be quite severe.
Here’s how you should safely open the coolant system caps.
- Wait for the vehicle to cool down (about 30 minutes)
- Take a rag, cloth, or towel and cover the still-closed cap.
- Unscrew the cap underneath your protective layer.
- Remove the cap and the rag to inspect the coolant.
You don’t need to use the cloth again when replacing the cap.
Why Is My Car Still Hot After Turning It Off?
It takes time for hot air to dissipate into the surrounding atmosphere. The colder and drier it is, the faster this process will happen.
In most normal circumstances, your engine will feel hot for about half an hour after you switch it off.
Don’t worry! It’s perfectly normal for your engine to still feel warm.
If two or three hours have gone by since you turned it off, that’s more unusual. You could get it checked out by a mechanic, but chances are it’s just how the vehicle’s been designed.
Some hoods trap heat much better than others. That’s all there usually is to it.
On many diesel vehicles, the fan will keep running after you turn the engine off. This usually happens on shorter journeys. It’s the car keeping itself cool while it manually works on the DPF regeneration cycle.
Again, it’s nothing to worry about – but take your car for a longer journey as soon as possible. The DPF regeneration cycle often requires the vehicle to run at about 40 mph or more for 15 minutes.
How Long Does An Engine Take To Cool Down After Overheating?
If your engine overheats, it’ll take an hour or two to cool down completely.
Aid the cooling process by lifting the hood. This allows air to pass across more of the engine, removing more heat.
Whatever you do, don’t remove the radiator cap – as tempting as it might be. You’ll burn your hand and burn it severely.
You might be able to drive again once it cools. However, expect it to overheat again. Before you set off, top the coolant up with water and antifreeze if you have it.
You’ll need to find, address, and repair whatever’s causing the overheating in the first place. You should head straight to an auto shop.
How Long Does It Take A Car Interior To Cool Down?
The cabin of your car might have got too hot. Your car might have been sitting in the sun, or someone might have been blasting hot air through the heater fans.
It shouldn’t take long to cool down to a comfortable temperature.
If you want your car to cool down as quickly as possible, try:
- Parking in the shade.
- Opening all the doors or windows.
- Turning the air conditioning on (if applicable).
Your car should be at a comfortable temperature within five minutes.
Conclusion: How Long It Takes For Cars To Cool Down
Whatever your reason for waiting for your car to cool, it shouldn’t take too long.
You can usually consider a car to be cool within half an hour. It’ll take a little longer if the engine exceeds its operating temperature and overheats.
If your cabin is too hot, air it out. It’ll soon cool down. Turn on the A/C if you have it. If not, lowering the windows will have to do.
Finally, if you’re worried about the loud fan noises coming from your engine after you switch it off, it’s usually okay. Wait five or ten minutes. The fan will probably switch off by then.