How To Test For A Blown Head Gasket (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

TEST 2: Coolant Shooting Out Of Radiator

The second most common result of a blown head gasket is compression pressures or combustion gases escaping into the cooling system; by which I mean into the radiator.

For our second test, we'll remove the radiator cap, crank the engine and see if coolant is shot out of the radiator.

The result that will tell us everything fine is observing the coolant remaining undisturbed in the radiator when the engine is cranked.

IMPORTANT: This test must be done with a completely cold engine. Don't remove the radiator cap from the radiator if the engine has been running for any length of time.

This is what you need to do:

1. 1

   Remove the radiator cap from the radiator.
   
   CAUTION: The engine should be completely cold before you removing the radiator cap. Opening the radiator cap on a hot engine can spray hot coolant all over you and severely burn you.

2. 2

   Check the coolant level.
   
   If the coolant level is low, top it off with water before proceeding.

3. 3

   When ready, have your helper crank the engine as you observe the radiator from a safe distance.

4. 4

   You'll see one of two results:
   
   1.) The coolant is shot out of the radiator.
   
   2.) The coolant is not disturbed at all.

Let's take a look at your test results:

CASE 1: The coolant shot out of the radiator. This confirms beyond a shadow of a doubt that you do have a blown head gasket on your hands.

CASE 2: The coolant DID NOT shoot out of the radiator. So far so good. In TEST 1, you confirmed that coolant isn't mixing with the engine oil. In this test, you have confirmed that no exhaust gases are escaping thru' the radiator...

If you still think that you do have a blown head gasket on your 2.8L V6 S10/S15, read the next test. Go to: TEST 3: Engine Compression Test.

TEST 3: Engine Compression Test

It is not uncommon for a head gasket to burn (fail) at a point between two adjacent cylinders.

This type of head gasket failure will result in these two cylinders having 0 PSI compression due to the compression of one cylinder leaking into the other and vice versa.

We can easily verify if a head gasket has failed in this way by performing an engine compression test.

NOTE: The following tutorial will give you a more detailed explanation of the compression test: How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).

These are the steps:

1. 1

   Disable the fuel system and the ignition system.
   
   You can easily accomplish this disconnecting the two TBI fuel injectors and the distributor from their electrical connectors.

2. 2

   Disconnect the spark plug wires from their spark plugs.
   
   NOTE: Label the spark plug wires with the cylinder they belong to or you'll end up losing their firing order and now you have another problem to solve.

3. 3

   Remove the spark plugs.

4. 4

   Install the compression tester (hand tight only) on the first cylinder you're gonna test.

5. 5

   Have a helper crank the engine while you observe the compression tester.

6. 6

   Have your helper stop cranking the engine once the needle on the tester stops climbing.

7. 7

   Write down the compression readings. You can use the illustration above to record the number of the cylinder.

8. 7

   Repeat steps 4 through 7 on the next cylinders.

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

CASE 1: You got 2 side by side (adjacent) cylinders with 0 PSI. This confirms beyond a shadow of a doubt that you do have a blown head gasket on your hands.

CASE 2: All cylinders had sufficient compression. So far so good. All the tests you've done up until this point tell you that you don't have blown head gasket on your hands.

But, if you still suspect that you have a blown head gasket, I suggest doing a chemical block test as explained in the next test section: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).