If you do a pressure check, would bad coolant / radiator hoses cause the test to fail?

I have had 2 mechanics trying to figure out why I am losing cooling fluid. Pressure test didn't turn out any problems. One of the mechanics told me, that the cooling hoses are kind of stiff. But wouldn't bad hoses cause a pressure test to fail? Also would a pressure test be able to identify a blown head gasket? My assumption is that it should?

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    Welcome to Motor Vehicle Maintenance & Repair! A pressure test won't necessarily show a blown head gasket. There are other tests to prove that. There's a test which shows hydrocarbons in the coolant, which is an absolute proof positive way to show a blown head gasket (there's no other way for hydrocarbons to get into the coolant other than a blown head gasket). A pressure test won't exhibit an issue if the leak is so slow, there's no real way to notice it. By "2 mechanics", are you suggesting you've taken it to two different places, or are you saying 2 mechs at one shop? Commented Jun 28, 2018 at 21:44
  • 2 places. Maybe I should try the UV test next, after checking for blown head gasket? I want to have a good idea about the problem before I go to the third guy. Commented Jun 28, 2018 at 21:51

2 Answers 2


A pipe can have a really small hole which only starts leaking when the system is fully hot and therefore at full pressure - it then can release cookant which effectively instantly vapourises and leaves very little trace - except for the scald on your forearm as you get close to it... and that is how I found it - pain is a good educator...

So, be careful - leaks can be difficult to trace...


A short term pressure test may not show a small leak. Doing the pressure test overnight may show signs of small leaks, but can still be difficult to find, (the pressure dropped but can't find a leak). A blown head gasket may show up if the sparkplugs are removed and the system is pressurized. The coolant may collect in the cylinder bore. By turning the engine over slowly by hand you may see the coolant expelled by the piston.

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