How To Test Engine Compression (1997-2003 4.2L V6 Ford E150, E250)

Testing for a blown head gasket (and the 4.2L V6 engine has two) involves performing one or two of four tests. Two of those don't require any tools.

The remaining two tests are an engine compression test, which requires a compression tester, and a block test, which is done with a combustion leak detector.

In this tutorial, I'll explain how to do all four tests. While I hope your Ford van doesn't have a blown head gasket, if you do suspect it might, one of these four tests will help you confirm it.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.2L V6 Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
• 4.2L V6 Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003.

Symptoms Of A Blown Head Gasket

When one or both head gaskets fail, the engine will suffer one of three problems:

• Engine No-Start: The engine cranks but doesn't start.
• Engine Starts But Overheats: The engine starts but then overheats in no time for no good reason.
• Cylinder Misfire: The engine starts but runs with a misfire.

If the engine in your van starts and runs and one or both head gaskets are blown, you'll see one or more of the following symptoms:

• Overheating: One of the most noticeable symptoms is engine overheating. A blown head gasket can allow coolant to leak into the combustion chambers or oil passages, leading to inadequate cooling of the engine.
• White Smoke from the Exhaust: If coolant leaks into the combustion chambers, it can be burned along with the fuel, producing white smoke from the exhaust. This is often accompanied by a sweet smell.
• Milky Oil: Coolant mixing with engine oil can result in a milky or frothy appearance on the oil dipstick or under the oil filler cap. This indicates contamination and a potential head gasket leak.
• Loss of Coolant: If there's a head gasket leak, you may notice a gradual decrease in coolant levels without any apparent external leaks. Keep an eye on the coolant reservoir and radiator.
• Poor Engine Performance: A blown head gasket can cause the engine to run poorly, with symptoms such as rough idling, hesitation, or a noticeable decrease in power and acceleration.
• External Coolant Leaks: In some cases, coolant may leak externally from the engine, typically near the head gasket area. Look for signs of coolant puddles or stains under the vehicle.
• Bubbles in the Radiator or Overflow Tank: When the engine is running, air bubbles may be visible in the radiator or overflow tank if there's combustion gas leaking into the cooling system through a blown head gasket.
• Excessive Pressure in Cooling System: A blown head gasket can cause an increase in pressure within the cooling system, leading to bulging hoses, coolant overflow, or even radiator or hose ruptures.
• Compression Loss: A compression test can reveal low compression in one or more cylinders, indicating a potential head gasket failure.
• Check Engine Light: Depending on the severity of the issue, the engine's computer may detect abnormalities related to engine performance or emissions, triggering the check engine light.

TEST 1: Oil The Color Of Coffee With Too Much Creamer

This is the go-to test at all shops, and it's the first test I learned to check for a blown head gasket.

This test simply involves pulling out the engine oil dipstick and checking the color and viscosity of the oil sticking to the engine's oil dipstick.

If the oil is super thick and the color of a 'coffee with to much creamer', you've got a blown head gasket on your hands.

If the color of the oil is normal, we'll move on to TEST 2.

These are the steps:

1. 1

   Open the hood.

2. 2

   Pull out the engine's oil dipstick.

3. 3

   Check the color of the oil and how thick it is.

4. 4

   You'll see one of two things:
   
   1.) The oil on the dipstick is a creamy, off-white color and is thick as syrup.
   
   2.) The oil is its normal color and viscosity.

Let's see what your test result means:

CASE 1: The engine oil looks like 'coffee with too much creamer'. This confirms that one or more of the engine's head gaskets are blown.

CASE 2: The color of the engine oil is normal. This is the correct and expected test result.

The next step is to check to see if compression/exhaust gases are leaking into the cooling system. Go to: TEST 2: Exhaust Gases Shooting Out Of The Radiator.

TEST 2: Exhaust Gases Shooting Out Of The Radiator

One other common result of a blown head gasket is letting combustion gases or coolant pressures leak into the engine's cooling system.

This ends up causing a big buildup of pressure within the cooling system whenever the engine is cranking or running, leading to symptoms such as coolant leaks, swollen hoses, or even causing the radiator tanks to burst.

One of the most common ways to diagnose this problem is by taking off the expansion tank's cap and then cranking the engine.

If one or both head gaskets are compromised and letting compression gases enter the cooling system, you'll see the coolant forcefully expelled from the expansion tank.

The correct and expected test result is for the coolant to remain undisturbed (inside the coolant expansion tank) while your helper is cranking the engine.

CAUTION: Do not remove the expansion tank's cap if the engine is hot. If the engine has been running for any length of time, then let it cool down completely before removing the expansion tank's cap!

These are the test steps:

1. 1

   Remove the cap from the expansion tank.

2. 2

   Check the coolant level and add water if necessary.

3. 3

   Have your helper to crank the engine, while you stand at a safe distance from the open radiator.

4. 4

   You'll see one of two results:
   
   1.) The water or coolant inside the expansion tank will shoot up and out.
   
   2.) The coolant will not be disturbed. In other words, cranking the engine will have no effect on the level of the water or coolant in the expansion tank.

Let's examine your test result:

CASE 1: The coolant bubbled out or shot out from the expansion tank as the engine was cranked. This result confirms that one or both head gasket are blown.

CASE 2: The coolant DID NOT bubble out NOR shoot out from the expansion tank as the engine was cranked. This is the correct test result.

If the engine doesn't start, your next step is: TEST 3: Engine Compression Test.

If the engine starts and runs but overheats, your next test is: TEST 4: Using A Chemical Block Tester (Combustion Leak Tester).