How To Test For A Blown Head Gasket (2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 4.2L Chevrolet Trailblazer And 4.2L GMC Envoy)

Testing to see if your 4.2L Chevy Trailblazer or 4.2L GMC Envoy has a blown head gasket is not difficult at all.

In this tutorial I'm gonna' explain the four most common tests that are done to verify a blown head gasket.

Two of the four tests require no tools and can be done in a few minutes.

En Español You can find this tutorial in Spanish here: Cómo Probar El Empaque De Cabeza (2002-2009 4.2L Chevrolet TrailBlazer) (at: autotecnico-online.com).

Symptoms Of A Blown Head Gasket

In the majority of the cases, a blown head gasket is a direct result of severe engine overheating.

If the 4.2L engine on your Chevrolet TrailBlazer or GMC Envoy has overheated, and its head gasket is blown, you're going to see one or more of the following symptoms:

  1. Your Chevy Trailblazer (GMC Envoy) is overheating.
  2. White smoke is coming out of the tail-pipe and it smells like anti-freeze being cooked.
  3. Your Chevy Trailblazer (GMC Envoy) won't start. You've checked:
    1. All cylinders are being fed spark.
    2. All fuel injectors are injecting.
    3. Fuel pump is good.
  4. The engine oil looks like coffee with way too much creamer.

In some of the cases, a head gasket failure does not result from severe engine overheating.

It's very common for multi-layered steel gaskets to fail all on their own.

Your 4.2L Chevrolet TrailBlazer or GMC Envoy uses a type of gasket called multi-layered steel head gasket. These head gaskets are infamous for failing on their own and causing engine oil leaks between the cylinder head and block.

The two most common symptoms you're going to see when the multi-layered steel head gasket has failed on your 4.2L Chevrolet TrailBlazer or GMC Envoy are:

  1. Engine oil leaking from head gasket.
  2. Engine overheats for no apparent reason.

TEST 1: Engine Oil Mixed With Coolant

Engine Oil Mixed With Coolant. How To Test For A Blown Head Gasket (2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 4.2L Chevrolet Trailblazer And 4.2L GMC Envoy)

The most common symptom of a blown head gasket, that you're going to see, is the oil adhering to the engine oil dipstick looking like coffee with way too much creamer.

This oil condition is the direct result of the head gasket allowing engine coolant into the crankcase. Once the coolant is in the crankcase it'll mix with engine oil. The end result of this mixture is an engine oil that looks like coffee with way too much creamer.

So for our first test, we're going to check the color and condition of the oil adhering to the engine oil dipstick.

These are the test steps:

  1. 1

    Open your Chevy Trailblazer (GMC Envoy)'s hood.

  2. 2

    Pull out the engine oil dipstick.

  3. 3

    Check the color of the engine oil on the dipstick.

    You'll get one of two results: The engine oil will be mixed with coolant and will look like a coffee with way too much creamer. Or the engine oil will be its usual normal color.

Let's examine your test result:

CASE 1: The engine oil color is that of a ‘coffee with too much creamer’. This tells you that the head gasket is blown.

CASE 2: The engine oil color is normal. This is the correct test result and let's you know that coolant isn't mixing with the engine oil in the crankcase.

The next step is to see if coolant is being shot out of the radiator while cranking the engine. For this test go to: TEST 2: Coolant Shooting Out From Open Radiator.

Chevrolet Vehicles:

  • Trailblazer 4.2L
    • 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009

GMC Vehicles:

  • Envoy 4.2L
    • 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009