TEST 2: Coolant Shooting Out From Open Radiator

How To Test A Blown Head Gasket (2001-2005 1.7L Honda Civic)

The other very common end result of a blown head gasket is compression/combustion pressures escaping through the cooling system instead of being contained in the cylinder.

This can be very easily verified by checking to see if these pressures are making the coolant shoot out of your Honda Civic's radiator (with cap removed).

If indeed the coolant is being shot out of the radiator while you're cranking your Civic's engine then you've confirmed that the head gasket is blown.

IMPORTANT: If your Honda Civic has been running for an extended amount of time, let the engine cool down for at least an hour! Do not remove the radiator cap from a hot radiator or a hot engine.

There's a good chance that your Honda is not starting, in this case... you don't have to worry about a hot engine.

  1. 1

    Remove the radiator's cap. Check to see if there is coolant in the radiator. If the radiator is empty... add some water or coolant to bring it up to the radiator's neck level.

  2. 2

    Crank the engine with the help of helper, while you stand at a safe distance from the open radiator.

  3. 3

    You'll see one of two results:

    1.) The water or coolant inside the radiator will shoot up and out of the now open radiator.

    2.) The coolant will not be disturbed. In other words, cranking the engine will have no effect on the level of the Water or coolant in the radiator.

OK, now that the testing part is done... let's take a look at what your results mean:

CASE 1: The coolant bubbled out or shot out from the radiator: This unfortunate test result tells you, without a shadow of a doubt, that your Honda Civic's head gasket is blown.

This test result only happens when the head gasket has blown and/or the cylinder head has warped due to the engine overheating. No further testing is required.

The normal/correct test result is for the coolant to remain undisturbed (inside the radiator) no matter how long you crank the cold engine.

CASE 2: The coolant DID NOT bubble out NOR shoot out from the radiator: If cranking the engine had no visible effect on the level of the coolant in the open radiator, this is normal.

If you were to ask 10 persons, what is the most common symptom of a blown head gasket, 9 out 10 would say, without hesitation, engine oil mixing with coolant and engine compression/ combustion gases shooting out of an open radiator neck and yes they would be right but not in all of the cases. There are times when this doesn't happen and so the next test will help to further verify this, GO TO: TEST 3: Engine Compression Test.

TEST 3: Engine Compression Test

How To Test A Blown Head Gasket (2001-2005 1.7L Honda Civic)

If your 1.7L Honda Civic starts and runs, skip this test and go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

If your Honda Civic overheated and now it doesn't start, the next test is a compression test of all 4 cylinders.

Why a compression test? Because the head gasket has burned at a point between two cylinders, the resulting gap in the head gasket will let the compression/combustion of one cylinder to leak into the other and vice-versa.

The end result of this is that those two cylinder end up with 0 PSI compression and the engine not starting.

This particular problem leads a lot of folks to misdiagnose a blown head gasket on their Honda because it doesn't cause the engine oil wasn't mixed with coolant and the engine coolant wasn't being shot out of the radiator (with cap removed).

This condition can be very easily verified by doing a compression test. In this test step I'll show you how and more importantly, how to interpret the compression test results to see if the head gasket is burned or not. This is what you'll do:

  1. 1

    Remove all four COP ignition coils.

    Remove all four spark plugs too.

  2. 2

    Thread in the compression tester by hand, on the first spark plug hole you're gonna's start with.

    Do not use any tools to tighten the compression tester. Hand tightening the compression tester is more than enough to get the proper results.

  3. 3

    Have a helper crank the engine. Your job is to keep your eyeballs on the compression tester. The needle will climb, as the engine cranks, till it reaches the maximum cylinder compression. At the point it stops climbing, have your helper stop cranking the engine.

    On a piece of paper, write down the reading and what cylinder it belongs to (you can use the image in the image viewer to help you identify the cylinder). Repeat the above steps in the remaining 3 cylinders.

If your Honda's head gasket is burned at a location between 2 cylinders... your compression test readings will give you 2 good compression readings and 2 compression readings that will be 0 PSI. Let me give you a more specific example:

Let's say that I tested my Honda and I got the following cylinder compression readings:

  1. Cylinder #1 = 175 PSI
  2. Cylinder #2 = 165 PSI
  3. Cylinder #3 = 0 PSI
  4. Cylinder #4 = 0 PSI

As you can see from the above compression readings, cylinders #3 and #4 have 0 PSI readings. And this is a clear indication that the head gasket has burned at the point between them both. Now, in your specific case... you may not see those exact same cylinders with 0 PSI readings. It may be #1 and #2 or it may be #2 and #3... the main idea is that whatever cylinders are affected, they will always be side by side.


CASE 1: All cylinder compression readings where normal: These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.

If you still suspect that your 1.7L Civic has a blown head gasket issue, take a look at the next test: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

CASE 2: Two side by side cylinders had 0 PSI compression: This engine compression reading confirms that the head gasket is burned thru' at the point between those two cylinders. You will need to replace the head gasket.