How to Find a Slow Coolant Leak


coolant, slow coolant leakSlow Coolant leaks are extremely difficult to diagnose.  Unlike leaking oil, slow coolant leaks leave barely any residue behind.  Coolant is half water and it’s other ingredients that don’t form a sticky residue so the slow leaks usually don’t leave an evidence trail.

There are two things that can easily be confused with a slow coolant leak:

  1. Evaporating Coolant
  2. A Blown Head Gasket

As the coolant in your vehicle expands as it gets hot it is forced out of your radiator into the coolant overflow tank or degas tank.  This hot coolant sitting in this overflow tank will always evaporate slowly causing the coolant level to slowly drop. If your coolant level drops slowly and always has, you most likely are just losing coolant to evaporation.

Blown head gaskets can also cause coolant to slowly get drawn into your engine causing a similar slow loss of coolant.  If you have a blown head gasket it will have other symptoms so try reading our article on symptoms of a blown head gasket to tell if that is the problem you have.

If your coolant isn’t evaporating and you don’t have a blown head gasket, then you must have a slow coolant leak.

How to Find a Slow Coolant Leak

  • Cooling system pressure test
  • Dye Test

A cooling system pressure test is the easiest way to find a slow coolant leak.  Many auto parts stores will rent cooling system pressure testing equipment for a small fee or even for free.  With this testing equipment, you can pressurize your cooling system while it’s cold and carefully inspect the engine while it isn’t running which can often show a small leak quickly and easily.

If your leak is so small that a pressure test doesn’t reveal it’s location, try adding UV dye to your coolant and drive for a few hundred miles.  After driving for a while, use a UV light to check for traces of the dye.

If you find a slow coolant leak, use BlueDevil Coolant Stop Leak to quickly and easily stop the leak and keep your car running coolant and to keep you from having to buy another jug of antifreeze!

You can pick up BlueDevil Coolant Stop Leak at one of your local auto parts stores like:

  • AutoZone  
  • Advance Auto Parts
  • Bennett Auto Supply
  • CarQuest Auto Parts
  • NAPA Auto Parts
  • O’Reilly Auto Parts
  • Pep Boys
  • Fast Track
  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributor
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
  • Hovis Auto & Truck Supply stores
  • Salvo Auto Parts
  • Advantage Auto Stores
  • Genuine Auto Parts stores
  • Bond Auto Parts stores
  • Tidewater Fleet Supply
  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

Pictures Provided By:

coolant_leak.jpg – By Pixygrilly – Licensed by Getty Images – Original Link

2 responses to "How to Find a Slow Coolant Leak"


  1. S. T. Mimes on February 5, 2020 at 11:21 am

    I truly love Blue Devil products. I have saved and prolonged at least 3 vehicle using BD head gasket repair and stop leak. Thanks for the continued research and advanced use of these products.

    • BlueDevil Pro on February 5, 2020 at 11:54 am

      S.T. –

      Thank you for sharing! We appreciate your feedback and are happy to hear that our products have been able to seal the leaks on your vehicle’s on multiple occasions. Once the product seals, it would be a permanent seal.

      Thank you!


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