How To Test For A Blown Head Gasket (1991-2011 4.0L Ford Ranger And Mazda B4000)

TEST 2: Coolant Shooting Out From Open Radiator

The second most common symptom of a blown head gasket is engine compression/combustion pressures escaping into the cooling system.

You can easily confirm this condition by removing the cap from the radiator and then cranking the engine.

If the coolant (inside the radiator) gets shot out while cranking the engine, your 4.0L Ford Ranger (Mazda B4000) has a blown head gasket problem.

IMPORTANT: Do not remove the radiator cap from the radiator if the engine is hot or has been running for any length of time.Let the engine cool down completely before removing the cap from the radiator.

Let's get started:

1. 1

   Remove the radiator's cap.

2. 2

   Check the coolant level in the radiator. If the radiator is empty then add some water or coolant.

3. 3

   Have your helper crank the engine while you stand at a safe distance from the open radiator.

4. 4

   You'll see one of two results:
   
   1.) The water or coolant inside the radiator will shoot out of the open radiator.
   
   2.) The coolant remained undisturbed. In other words, cranking the engine will have no effect on the level of the water or coolant in the radiator.

Let's examine your test result:

CASE 1: The coolant shot out from the radiator as you cranked the engine. This confirms that one or both head gaskets are blown on your 4.0L Ford Ranger (Mazda B4000).

CASE 2: The coolant DID NOT shoot out from the radiator. This is the correct and expected test result.

If your 4.0L Ford Ranger (Mazda B4000) starts but runs with a misfire, then next step is to test engine compression. For this test go to: TEST 3: Engine Compression Test.

If the engine starts but overheats almost immediately, then your next step is to do a 'block' test. For this test go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

TEST 3: Engine Compression Test

You'll notice that the photo of the blown head gasket I'm using at the beginning of this tutorial is burned in a spot between two cylinders.

Although this type of head gasket failure does not occur very often, it does happen.

When this failure occurs, the two affected cylinders produce 0 PSI compression. As a result, the engine usually starts but runs with a misfire.

You can easily confirm this type of head gasket failure by doing an engine compression test.

These are the test steps:

1. 1

   Disable the ignition system by disconnecting the ignition coil from its engine wiring harness connector.

2. 2

   Remove all of the spark plugs
   
   NOTE: Before you disconnect the spark plug wires, label them with the cylinder number they belong to. You'll avoid losing the spark plug wires' firing order when it's time to put things back together.

3. 3

   Install the compression tester by hand in the spark plug hole of cylinder #1.
   
   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 your helper crank the engine.
   
   The needle on the tester will climb as the engine cranks. Once the cylinder reaches its maximum compression the needle will stop climbing.
   
   Once it stops climbing have your helper stop cranking the engine.

5. 5

   Write down the reading and what cylinder it belongs to (you can use the illustration above to help you identify the cylinder).

6. 6

   Repeat steps 3 through 5 in the remaining cylinders.

Let's take a look at what your test results mean:

CASE 1: All cylinder compression readings were above 0 PSI. This is the correct and expected test result.

Your next step is to perform a block test with a block tester. 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 test result confirms that the head gasket (of that bank of cylinders) is burned at the point between those two cylinders.

You'll need to replace both head gaskets.