How To Test A GM 3.1L, 3.4L for a Blown Head Gasket

A blown head gasket will make your 3.1L or 3.4L GM car or minivan over-heat and/or Not Start. On your vehicle, you probably have already replaced the water pump, or the thermostat or the fan motor or know that all these are OK and yet the car or mini-van is overheating.

So to help you troubleshoot this issue, in this article, I'm gonna' show you four of the most common tests that are done to confirm a blown head gasket on any overheating 3.1L or 3.4L GM car or mini-van. Two of them require absolutely no tools to do, the third requires a compression tester and the last is a block test with a combustion leak detector.

So that you can navigate this article, here are its contents at a quick glance:

  1. Symptoms Of A Blown Head Gasket.
  2. TEST 1: Checking The Color Of The Engine Oil.
  3. TEST 2: Compression Gases Shooting Out From an Open Radiator.
  4. TEST 3: Engine Compression Test.
  5. TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).
  6. Related Test Articles.

En Español You can find this tutorial in Spanish here: Cómo Probar el Empaque de la Cabeza (GM 3.1L, 3.4L) (at:

Symptoms Of A Blown Head Gasket

The most common cause of a blown head gasket is that the engine overheated because: 1) Fan clutch is not working, 2) All of the coolant leaked out of the engine and you kept driving it this way. 3) Thermostat went BAD and is stuck closed and the coolant could not circulate. The most common symptoms a blown head gasket are:

  1. 1

    Your 3.1L, 3.4L GM car or mini-van is overheating. You know it's not the fan (or fan clutch) or thermostat.

  2. 2

    White smoke is coming out of the tail-pipe and it smells like anti-freeze being cooked.

  3. 3

    Your 3.1L, 3.4L GM car or mini-van won't start.

    1.) You have already verified it's not an ignition system problem because you have spark coming out at all of the spark plug wires.

    2.) You know it's not a Lack of Fuel, because you have verified that the fuel pump is delivering fuel to the fuel injectors.

  4. 4

    The engine oil is thick and tan to off-white color (mixed with coolant).

TEST 1: Checking The Color Of The Engine Oil

Oil Mixed with Coolant Test. GM 3.1L, 3.4L for a Blown Head Gasket

Before you start, let me tell you that although there are three tests in this article, you'll probably not have to do all three. This is because if the first or second test confirms you have a blown head gasket on your 3.1L or 3.4L GM car or mini-van... there's no need to do the third.

Before you do this first test... take a look at the entire article. The first two test should take you less than 5 minutes to do. Also, whether your GM car or mini-van starts or not... all three tests apply.

OK, on with show... this is what you need to do:

  1. 1

    Raise the hood on your car or mini-van and once open, pull out the engine's oil dipstick.

  2. 2

    What you need to do is to verify the color of the engine oil and its viscosity. This simple and easy test will give you one of two results:

    1.) The engine oil will not be its normal color, but a tan/off white milky color...

    2.) Or it's gonna' look normal.

OK, let's go into a deeper explanation of what these two results mean:

CASE 1: The engine oil is a milky off-white/tan color, and if your vehicle is overheating (or not starting) this tells you that the head gasket is history. You're gonna' have to tear the cylinder heads off of your car or mini-van.

Why does the oil look like this? Mainly because your GM 3.1L, 3.4L car or mini-van got too hot and :

1.) The cylinder head (or heads) warped. Once this happens, the head gasket burns.

2.) If the head gasket(s) can not keep the engine oil, coolant, engine compression, or exhaust gases separate, these things will mix with each other...

3.) ...this will lead to the coolant entering the engine oil pan.. As both oil and coolant mix... the resulting combination gets thick and becomes an off-white color.

CASE 2: The color of the engine oil is normal, but your vehicle is still overheating... I suggest doing the two other tests I'm presenting in this article. Go to TEST 2: Compression Gases Shooting Out From an Open Radiator.

Here's why: This is always the very first test that most Automotive Mechanics or Technicians do to easily diagnose a blown head gasket... even we (or they) know that a blown head gasket doesn't always result in oil mixing with the coolant. Thankfully, there are more easy and simple tests to continue checking for a blown head gasket.