Can You Add Coolant to a Hot or Overheating Engine?

Maybe you notice coolant leaking and the level dropping in your car, or maybe your car has shown signs of overheating, possibly leaving you stranded. Can you keep adding coolant to your engine if it’s leaking, or can you add more to get to your destination? Can you add coolant to a hot engine? Find out the answers to these questions in this article and video.

Can You Add Coolant to a Hot Engine?

Mechanic reviewing if you can keep adding coolant to an engine if it's leaking coolant or overheating

Wait until the engine is cool before opening the radiator cap or reservoir cap to add coolant. The cooling system is pressurized, and if the engine is still hot, coolant can spray up and harm you.

Can You Add Coolant to an Overheating Engine?

It Can Prolong Leaks and Damage More Parts

Adding coolant without fixing the leak can turn a minor problem into a major one. You can see at the beginning of the video in this article coolant stains of green and white on and near the engine block. It’s an indication of a large leak. A UV light exposes the leak in the dark, and you can see it with yellow lens, showing that coolant has been leaking for more than just a few days. This is also a sign coolant isn’t leaking from a small area like a hose clamp, and prolonged leaks can create more problems, like a faulty head gasket or warped engine head.

How to Find a Coolant Leak

3 methods to find or identify a coolant leak

  1. Pressure Test the System

    If you notice the coolant level keeps dropping but not obvious signs of a leak, you can check your engine for coolant leaks. Pressure testing the system will show where coolant is leaking from as parts are under pressure. You may find coolant is seeping and not leaking huge puddles on the ground, but, as shown in our example, it can create a major problem over time.

    More on how to find coolant leaks

    More on radiator pressure tests

  2. Try a Combustion Test

    You can also try a combustion test to see if combustion is mixing with the coolant. The steps involve connecting a tester tool with a low level of coolant, running the car, and pumping the tester. The tester will have bubbles, which is a sign that it’s taking in air, and it’ll change color if they’re mixing.

  3. Check the Oil Dipstick for a Creamy Color

    You can also check the oil dipstick to confirm if engine oil is mixing with coolant. Remove the dipstick and check the oil. A creamy color is a sign the fluids are mixing.

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Can You Add Coolant to a Hot or Overheating Engine? - 1A Auto
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Can You Add Coolant to a Hot or Overheating Engine? - 1A Auto
If you want to know if you can add coolant to a hot or overheating engine if the coolant level keeps dropping, find out if it's okay with these expert tips from the mechanics at 1A Auto
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