Blown Head Gasket Tests (2002-2004 4.2L Oldsmobile Bravada, 2004-2007 4.2L Buick Rainier)

TEST 2: Coolant Shooting Out From Open Radiator

The second most common test, that automotive repair technicians perform when testing for a blown head gasket, is to check if coolant gets expelled from the radiator while cranking the engine.

The correct and expected test result is for the coolant to remain undisturbed (in the open radiator) when cranking the engine.

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 cap.

2. 2

   Check the coolant level in the radiator.
   
   Add water or coolant if necessary.

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 the head gasket is blown on your 4.2L Oldsmobile Bravada (Buick Rainier).

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

If the engine, in your 4.2L Oldsmobile Bravada (Buick Rainier), 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

In a few cases, the head gasket fails in a section between two cylinders.

This type of failure will cause the two side-by-side cylinders to produce 0 PSI compression.

The engine may start, but it's going to run rough since it's only running with four instead of six cylinders.

We can troubleshoot this type of head gasket failure by doing an engine compression test.

These are the test steps:

1. 1

   Remove the ignition coils.

2. 2

   Remove all six spark plugs.

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.

Replace the head gasket.