How To Test For A Blown Head Gasket (1997-2010 4.6L, 5.4L Ford F150, F250, And F350)

TEST 3: Checking Cylinder Compression

In some cases, the head gasket fails in a spot right between two cylinders. The interesting thing is that the engine still starts and runs, but runs with a misfire.

Additionally, the head gaskets still keep the coolant from entering the crankcase and prevent the compression pressure from entering the cooling system. So, you won't see the engine oil turned a milky-white color, and you won't see the coolant being expelled from the coolant expansion tank.

The only symptom you'll notice is that the engine runs with two dead cylinders, which are side-by-side in the same bank.

The only way to confirm this type of head gasket failure is by performing an engine compression test on those two cylinders (we don't need to test all eight).

OK, let's get started:

1. 1

   Identify the side by side 'dead' cylinders.

2. 2

   Disable the ignition system to prevent the engine from starting.
   
   If you have the two coil pack setup (4.6L engines), then you need to disconnect both coil packs from their electrical connector.
   
   If your 4.6L, 5.4L has the COP ignition coils, disconnect all eight ignition coils from their electrical connectors to disable the ignition system.

3. 3

   Disable the fuel system.
   
   You can do this by disconnecting the fuel injectors or by removing the fuel pump relay.

4. 4

   Remove the spark plugs of those two side-by-side 'dead' cylinders.
   
   NOTE: Be careful and don't drop any on the floor or the spark plug's porcelain insulator can break (and then you'll have a misfire on your hands later).

5. 5

   Thread in the compression tester by hand, on the first spark plug hole you're gonna start with.
   
   Do not use any tools to tighten the compression tester. Hand tightening the compression tester is more than enough to get the proper results.

6. 6

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

7. 7

   Stop cranking the engine once the compression tester's needle stops climbing.
   
   Now, write down the reading and what cylinder it belongs to (you can use the illustration above to help you identify the cylinder) on a piece of paper.

8. 8

   Remove the compression tester and repeat the above steps in the other cylinder.

Let's take a look at your test results:

CASE 1: All cylinder compression readings where normal. These compression gauge readings confirm that the head gasket is OK and not burned at a point between two cylinders.

If still suspect a blown head gasket, take a look at the block test here: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).

CASE 2: Two side by side cylinders had 0 PSI compression. This engine compression reading confirms that the head gasket is burned thru' at the point between those two cylinders. You'll need to replace the head gasket.

Let me give you a more specific example: If the head gasket is burned at a location between 2 cylinders, your compression test readings will give you 2 good compression readings and 2 compression readings that will be 0 PSI. Let me give you a more specific example:

Let's say that I tested my Ford pick up and I got the following compression tester readings:

• Cylinder #1 = 165 PSI
• Cylinder #2 = 180 PSI
• Cylinder #3 = 0 PSI
• Cylinder #4 = 0 PSI
• Cylinder #5 = 170 PSI
• Cylinder #6 = 170 PSI
• Cylinder #7 = 175 PSI
• Cylinder #8 = 175 PSI

The compression readings for cylinders #3 and #4 would be a dead giveaway that the head gasket got fried between those two cylinders. Now, in your Ford pickup, you may not see those exact same cylinders with 0 PSI readings. It may be #1 and #2 or it may be #5 and #6, the key here, is that whatever cylinders are affected, two of them will have 0 PSI compression and they will be both be side by side.

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

There are times when one or both of the head gaskets fail but don't present any of the symptoms that the three previous tests are designed to confirm. To be more specific:

• The engine oil isn't mixed with coolant.
• The coolant isn't getting shot out of the expansion tank (when the engine is cranked with the expansion tank cap removed).
• The engine's idle is smooth.

The only symptom you'll notice is that the engine overheats within minutes of starting it. In these cases, the only way to pinpoint the overheating issue to a blown head gasket is with a block test.

This block test is done with a combustion leak detector. In a nutshell, this is how a block tester works:

• A blue liquid chemical, which is blue in color, is placed in the tester (see photo above).
• The tester assembly is then placed on the open radiator neck (you may have to drain some of the coolant in the radiator since this tool needs to 'gulp' some of the air inside the radiator).
• The engine is started.
• The rubber bellow is then squeezed to suck in the air up through the two fluid-filled chambers. As the air bubbles up through the fluid, it will cause a chemical reaction.
• If the blue chemical turns yellow (for gasoline engines), combustion gases are entering the radiator. This result confirms a head gasket failure, a cracked block, or a cracked cylinder head issue.
• If the blue chemical doesn't change color, you can conclude that you don't have a head gasket failure, a cracked block, or a cracked cylinder head issue.

You can buy one here:

More 4.6L/5.4L Ford F150, F250, And F350 Tutorials

There are quite a few 4.6L, 5.4L V8 F-Series pickup 'how to' tutorials and wiring diagrams you can find here:

• 4.6L, 5.4L Ford F150, F250, And F350 Index of Articles.

E-Series Vans: You can find all of the available tutorials and wiring diagrams for the 4.6L and 5.4L V8 E-Series vans in this index:

• 4.6L, 5.4L Ford E150, E250, And E350 Index of Articles (at: troubleshootmyvehicle.com).

Crown Vic/Grand Marquis: You can find all of the available tutorials and wiring diagrams for the 4.6L V8 Ford Crown Vic and Mercury Grand Marquis in this index:

• 4.6L Crown Victoria And Grand Marquis Index of Articles (at: troubleshootmyvehicle.com).