How To Test For A Blown Head Gasket (1991-1999 1.6L Nissan Sentra)

A blown head gasket is usually the result of severe engine overheating, but not always. If you suspect that your 1.6L Nissan's head gasket is blown, this tutorial will show you how to find out for sure.

The 4 tests, in this tutorial, are the standard blown head gaskets tests that the majority of auto repair technicians perform and you can do these yourself.

You can find this tutorial in Spanish here: Cómo Verificar un Empaque de Cabeza Quemado (1.6L Nissan Sentra) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 1.6L Nissan Sentra: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999.

Symptoms Of A Blown Head Gasket

From experience, I can tell you that head gasket problems fall into one of two categories: either the engine runs but overheats (for no apparent reason) or the engine doesn't start.

There are several symptoms, that you'll see when the head gasket gets blown on your 1.6L Nissan. These are:

1. Overheating.
2. Oil mixed with coolant.
3. White smoke coming out of the tail-pipe.
4. Engine cranks, but does not start.
5. No compression on two adjacent cylinders.
6. Coolant being pushed forcibly into the coolant reservoir bottle whenever the engine idles or the engine is turned off.

TEST 1: Engine Oil Mixed With Coolant

As you're already aware, coolant and motor oil pass from the block into the cylinder head thru' passages in them. One of the head gasket's job is to keep both of these from entering the cylinder and from mixing with each other.

When your vehicle overheats to the point that the aluminum cylinder head warps and/or the head gasket burns, these 2 fluids will mix.

Since this is one of the most common end results of a blown head gasket, it's the one that we're gonna' check first:

1. 1

   Open the hood of the car.

2. 2

   Pull out the engine oil dipstick.

3. 3

   Check the color of the oil sticking to the dipstick.

4. 4

   You'll see one of two things:
   
   1.) The color of the oil will be a milky white color (like coffee with too much cream).
   
   2.) The color of the oil will be its normal color.

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

CASE 1: The engine oil was a milky white color. This tells you that the coolant is mixing with the oil and that you do have a blown head gasket on your hands.

CASE 2: The engine oil was its normal color. This doesn't confirm anything just yet. You'll need to go to the next test to make sure. Go to: TEST 2: Coolant Shooting Out Of Radiator.

TEST 2: Coolant Shooting Out Of Radiator

As the engine turns, it's combustion cycle produces several different pressures (compression, combustion, exhaust, etc.). These gases/pressures are kept from entering the cooling system by the head gasket.

When the head gasket fails, it can no longer keep them sealed within the cylinder. Thus, they enter the cooling system thru' the cooling system passages in the cylinder head and block.

So, for our 2nd head gasket test, we'll check to see if the compression/exhaust pressure are trying to escape via the radiator.

These are the test steps:

1. 1

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

2. 2

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

3. 3

   Stand at a safe distance from the engine but within view of the radiator.

4. 4

   When ready, have your helper crank the engine.

5. 5

   You'll see one of two results:
   
   1.) The coolant shoots out when the engine was cranked.
   
   2.) The coolant was not disturbed at all.

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

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.

Your next step depends on one of two things:

• If the engine does not start, go to: TEST 3: Engine Compression Test.
• If the engine starts and runs, but overheats for no apparent reason, go to: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

TEST 3: Engine Compression Test

In a few instances, over the past few years, I have diagnosed vehicles with a blown head gasket that did not have coolant mixing with the oil and were not shooting the coolant out of the radiator when the engine was cranked.

Yet a blown head gasket they did have and the most important factor that all of these vehicles shared was that they had severely overheated.

OK, the test involves doing a compression test to see if two adjacent cylinders have 0 compression. I want to emphasize this, because this is important: Two adjacent cylinders will have 0 PSI compression.

This happens because the head gasket burns between two cylinders and thus the compression from one cylinder escapes into the other and vice versa.

NOTE: You can find a more detailed explanation of how to do a compression test and how to interpret its results here: How To Test Engine Compression (1991-1999 1.6L Nissan Sentra).

OK, let's begin:

1. 1

   Disable the fuel system.
   
   You can do this by disconnecting the fuel injectors from their connectors.

2. 2

   Disable the ignition system. Disconnect the distributor from its electrical connectors.
   
   NOTE: This is important, don't proceed to the next step without doing this.

3. 3

   Remove the spark plugs.

4. 4

   Install the compression tester (hand tight only) on the first cylinder you're gonna' test.
   
   NOTE: Hand tighten the compression tester in the spark plug hole, don't use any tools.

5. 5

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

6. 6

   When the needle stops moving, have your helper stop cranking the engine.

7. 7

   Write down the compression readings.

8. 8

   Repeat on the next 3 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. After having done 3 tests, you have confirmed that you do not have a blown head gasket. But (and you know there's always one) if your vehicle is still overheating for no apparent reason, take a look at the next section: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

TEST 4: Using A Chemical Block Tester (Combustion Leak Tester)

There are times when the vehicle does have a head gasket issue yet the 3 previous tests don't pinpoint it. In situations like these the only way to make absolutely sure the head gasket is blown is by doing a chemical block test.

The combustion-leak (block) tester is the go-to method in most (if not all) repair shops for confirming a blown head gasket. In a nutshell, here's how it works:

• A special test fluid —usually a bright blue one in color— gets poured into the tester (see photo above).
• The tester assembly is set on the open radiator neck (you may need to draw off a bit of coolant so the tool can "gulp" the air trapped in the radiator).
• Fire up the engine.
• Squeeze the rubber bulb to pull radiator air up through the two fluid-filled chambers; the bubbling air triggers a chemical reaction.
• If the blue fluid turns yellow (on gasoline engines), combustion gases are making their way into the radiator —confirming a head gasket failure, cracked block, or cracked cylinder head.
• If the blue fluid stays blue, you can rule out a head-gasket failure, cracked block, and cracked head.

You can pick up the fluid and tester at most auto-parts stores —or grab one online right here:

Frequently Asked Questions

1.)  How can I tell if the cylinder head is cracked?

The cylinder head has to be removed and visually inspected. If the crack is wide enough, you'll be able to easily see it.

Sometimes, a visual inspection proves inconclusive, this is why it's important to let a machine shop pressure test it for you.

2.)  Do I need to resurface the cylinder head?

YES, you need to resurface the cylinder head! You should never reinstall the cylinder head or cylinder heads without first having an automotive machine shop resurface the cylinders heads (particularly over an overheating condition).

Now, of course, if you (or the machine) have checked it with a straight-edge and there's no warpage, then and only then is the cylinder head not resurfaced.

More 1.6L Nissan Sentra Tutorials

You can find a complete list of 1.6L Nissan Sentra diagnostic tutorials in this index:

• 1.6L Nissan Sentra Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Idle Switch (1997-1999 1.6L Nissan Sentra).
• How To Test Engine Compression (1991-1999 1.6L Nissan Sentra).
• How To Test The TPS (1997-1999 1.6L Nissan Sentra).
• Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999) (at: easyautodiagnostics.com).