How to Test for a Blown Head Gasket
(Jeep 4.0L)

How to Test for a Blown Head Gasket (Jeep 4.0L)

This article will present you with the four most common ways to test for a blown head gasket on a Jeep 4.0L inline 6 cylinder engine.

All four are very simple and easy tests that will help you confirm (or disconfirm) a blown head gasket.

Two of the tests you can do in about 5 minutes or less and don't require any tools. The third blown head gasket test requires doing a compression test, for which you'll need a compression tester. The fourth is done with a combustion leak detector (block tester). Before you start any of them, take a look at the entire article first.

Here are the contents of this article at a quick glance:

  1. Symptoms of a Blown Head Gasket.
  2. HEAD GASKET TEST 1: Is Engine Oil Mixed with Coolant?
  3. HEAD GASKET TEST 2: Coolant Shooting Out of Open Radiator.
  4. HEAD GASKET TEST 3: Compression Test.
  5. HEAD GASKET 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 un Empaque de Cabeza Quemado (4.0L Jeep) (at: autotecnico-online.com).

Symptoms of a Blown Head Gasket

The most common cause of a blown head gasket is that the engine overheated due to: 1) a BAD radiator fan or fan clutch 2) No coolant in the engine due to a leak somewhere in the coolant System 3) Bad thermostat. The most common symptoms a blown head gasket are:

  1. Your Jeep is overheating. You know it's not the fan or thermostat.
  2. White smoke is coming out of the tail-pipe and it smells like Anti-Freeze being cooked.
  3. The Jeep 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. The engine oil is thick and tan to off-white color.

HEAD GASKET TEST 1:
Is Engine Oil Mixed with Coolant?

How to Test for a Blown Head Gasket (Jeep 4.0L)

One of the most common symptoms of a blown head gasket is coolant mixing with the engine oil and this first test will check for that.

OK, to get this show on the road, this is what you need to do:

  1. 1

    Open the hood on your Jeep 4.0L Wrangler (or Cherokee, Grand Cherokee) and once open, pull the engine oil dipstick.

  2. 2

    Now, look at the color of the oil (that's sticking to the dipstick) and see if:

    1.) The color of the oil is the color of coffee with too much cream (a milky white/tan color) or...

    2.) The color of the oil is its normal color.

OK, let's take a look at what the color of the engine oil means:

CASE 1: The color of the oil is a light tan, like coffee with too much cream, this result verifies that the head gasket is Blown on your Jeep 4.0L Grand Cherokee (or Wrangler or Cherokee). You can stop here, since no further testing is required.

As mentioned earlier, the reason the oil looks this way is:

1.) The engine in your Jeep severely overheated, resulting in the cylinder head warping. This in turn causes the head gasket to burn.

2.) Since the job of the head gasket is to seal Compression/Exhaust Gases, engine oil and coolant, a burned head gasket won't be able to keep any of them separated.

3.) This leads to the coolant entering the engine oil pan and mixing with the oil. As both of these mix... the resulting oil gets thick and turns to an off-white color.

CASE 2: The color of the oil is its normal color, So far so good, but it doesn't exonerate the head gasket yet, go to HEAD GASKET TEST 2.

Here's why: Although coolant mixing with the engine oil is a common result of a blown head gasket, this doesn't happen in all of the cases. Your Jeep 4.0L Cherokee (or Grand Cherokee, Wrangler) could have a blown head gasket and yet the engine oil doesn't show a trace of having mixed with coolant. Thankfully, there are several more tests you can do to further verify a blown head gasket.

Jeep Vehicles:

  • Cherokee 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
  • Comanche 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992
  • Grand Cherokee 4.0L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

Jeep Vehicles:

  • Wagoneer 4.0L
    • 1987, 1988, 1989, 1990
  • Wrangler 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

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