TEST 2: Coolant Shooting Out From
Open Radiator

Coolant Shooting Out From Open Radiator. How To Test For A Blown Head Gasket (Mazda 2.0L)

In this test section we're gonna' see if the engine's compression or combustion gases are entering the cooling system (if the head gasket is blown).

When this happens... you'll have coolant shooting out violently from the radiator (with the radiator cap removed of course).

IMPORTANT: Never remove the radiator cap from a hot radiator! If your Mazda 2.0L 626 starts and runs and it's been running for an extended amount of time, let the engine cool down for at least an hour. If the engine doesn't start, no need to worry about letting it cool down.

OK, these are the test steps:

  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

    Now, have a helper crank the engine, 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 is a clear indication that the 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.

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... then so far so good, since this is the normal result.

Your next step is to check engine compression. For this test, go to: TEST 3: Engine Compression Test.

TEST 3: Engine Compression Test

Checking Engine Compression To Test for a Blown Head Gasket (Mazda 2.0L)

There are times that when the head gasket gets blown... it just burns between two cylinders.

When this happens... you won't see the engine oil mixed with coolant nor will you see the coolant being pushed out of an open radiator (as you're cranking the engine). I have seen this enough to know that one more test has to be done.

To explain this a little further: When the head gasket has burned at a point between two cylinders, the resulting gap in the head gasket will let only the compression/ combustion of one cylinder leak into the other and vice-versa, but nothing else (like coolant). If this happens, in a Mazda 2.0L 626, this will cause a No Start Condition.

In this test step I'll show you how to test the engine compression and more importantly, how to interpret the results to see if the head gasket is burned or not.

This is what you'll do:

  1. 1

    The Ignition System must be disabled so that spark won't be created and delivered to the spark plug wires. The Mazda 626 covered by this tutorial comes with 2 types of ignition systems.

    Distributor type ignition system: You can do this by disconnecting the ignition coil's connector.

    Coil pack ignition system: Disconnect the ignition coil pack from its electrical connector.

  2. 2

    Remove all four spark plug wires and then remove all of the spark plugs.

  3. 3

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

  4. 4

    Have a helper crank the engine while you keep your eyes 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 Mazda 2.0L 626'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 Mazda 2.0L 626 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.

Your next test doing a block test. For this test go to: 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.