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There are lots of ways to diagnose a head gasket or to check the general health of an engine, but this video is focusing on 3 major systems.

1) The coolant system
2) The combustion chamber
3) The valvetrain

COOLANT SYSTEM PRESSURE TEST:

The boiling point of water (coolant) RISES under pressure. It’s imperative that the coolant system has NO AIR in it, no leaks, a known-good thermostat, and a good radiator cap in order to function properly. If the pressure stamped on your radiator cap is not being achieved, Boyle’s law is not taking affect, and your coolant will boil when the car is being driven at it’s normal operating temperature, and may exhibit signs of a blown head gasket. Many have cursed the process of burping all the air out, sometimes even taking several days and heat cycles to complete the process.

COMPRESSION TEST:

The point of a compression test is to diagnose the health of each combustion chamber. A compression test is a crude test to determine if a ring, valve seal, valve, or a head gasket problem exists. It will show immediately in this test because the gauge will not rise to the pressure specified for your engine. There are 3 numbers you need regarding your car’s setup.

High limit, Low Limit and Range.

The high limit is specified by your car’s manufacturer and reflects the equipment they used to build the engine. If you EXCEED the high limit, chances are it’s caused by excessive carbon build-up, and a Seafoam or MCCC treatment will usually remove the carbon and return it to an acceptable value. If that build-up isn’t caused by cheap gas, then it’s likely the car has an EGR problem or excessive oil blow-by leading to this situation.

The Low Limit represents the point in which the combustion chamber is not able to compress the engine’s specified fuel to the point where it can ignite it. Gasoline and air need to be compressed together in order for the energy stored in that fuel to be released. If it isn’t achieved, it will only burn, and not explode. Lower-than-Low Limit pressure means it’s time to rebuild the engine because one of the sealing components in the combustion chamber has failed or is in need of servicing. Either way, it’s expensive because working on the combustion chamber requires extensive disassembly or unusual tools that the average mechanic doesn’t have.

Range specifies how many PSI of variance there can be between ALL of your compression numbers. If there’s a large variance on one cylinder, then the engine will not run smoothly. If a cylinder is below spec, it may feel like a misfire even though the plug is getting spark. If all the values are close, the engine idles and revs more smoothly.

Aftermarket cams, pistons, head gaskets or machining will affect the results of your tests. A higher compression piston or thinner head gasket can raise the compression numbers slightly. A thicker head gasket or longer-duration cams will lower compression slightly. I don’t know how to determine exact numbers because I’m not an engineer, but you should remember that during testing if your engine is modified.

So in a nutshell, you want your numbers to be close and between the high and low limits. If a test fails, the only way to determine WHAT failed is to perform a leakdown test. Modifications to the factory internals or machining WILL change the OEM compression limit values, but NOT the range value.

LEAKDOWN TEST:

I’m not using a real leakdown tester in this video. A real leakdown tester has a regulator, a pressure gauge, a restrictor, and another pressure gauge. You measure the value of the post-restrictor gauge vs. the regulated supply and mark the percentage of pressure-drop. As a general rule, most cars are healthy around a 20% value. Race engines should be between 1-10% for highest performance.

I’m using the ghetto method for this test. Get the piston roughly at Top Dead Center, apply air pressure, fine tune TDC for that piston by turning the crank with a wrench to see if you can stop all of the airflow. Listen to the intake for leaking air to determine if there’s a bad intake valve. Listen to the tailpipe for leaking exhaust valves. If neither are leaking, but air is still flowing, remove the tool and pour a cap of oil into the spark plug hole so that it coats the rings to make a better seal. After oiling, re-install the tool and repeat the test to see if you get better results. If you do, you have bad rings. If you don’t, you have bad valve stem seals, a blown head gasket, or a cracked head. If you have a cracked head or bad head gasket, then there will likely be pressure venting through your coolant system. Taking off the radiator cap and watching for air rising to the filler neck will point you in the right direction.

This is your vehicle’s climate control panel. The Auto mode may be used all year round. To turn it ON, press this button for automatic cooling or dehumidified heating. The indicator light turns ON when the system is activated. It will automatically regulate and maintain fan speed, airflow and temperature in the cabin.

The AUTO function can be turned OFF by either changing the fan speed, or by pressing the DEFROSTER, MODE, or OFF buttons. To reactivate automatic control, press the AUTO button. To turn the system OFF completely, press the OFF button.

Your vehicle has separate temperature control buttons for the driver and front seat passenger. The driver’s temperature control will set the temperature for both driver and passenger if the dual control is not activated. Turn the driver’s side control knob to the right for warmer or left for cooler temperature. You’ll see the temperature setting change on the monitor.

If you want to adjust the passenger side temperature independently from the driver’s side, press the DUAL button or turn the temperature control knob left or right. The DUAL control indicator light will then illuminate. Turn the knob right for warmer or left for cooler temperature. The passenger’s side temperature will be displayed on the monitor. To switch back to driver control, press the DUAL button again. If in Dual mode when you turn your system off using the OFF button, it will resume Dual operation when turned back on using the AUTO button.

The manual airflow control button provides a choice of airflow outlets. Press repeatedly to cycle through these four choices:
• Air will flow from the center and side vents
• From center, side and foot vents
• Mainly from foot vents,
• From the defroster and foot vents

Your choices will be displayed on the monitor.

Press the A/C button to turn the air conditioning ON or OFF.

In hot or humid conditions, a visible mist may be seen coming from the vents. This does not indicate a malfunction.

Please be aware that the Air Recirculation feature will not activate while in Defrost mode because allowing outside air to enter the vehicle improves defogging performance.

Refer to the Automatic Intake Air Control chapter.

This button operates the fan speed. Press the right control button to increase fan speed and the left button to decrease fan speed. When you manually change fan speeds, it turns off the automatic climate control mode. To return to automatic climate control, press the AUTO button.

To defrost or defog the front and side windows, press the DEFROSTER button. The indicator light will illuminate. Airflow will be directed to the front and side windows.

In the DEFROST mode, the A/C activates automatically at temperatures above 23 degrees Fahrenheit, and the air recirculate mode automatically turns off allowing outside air to be drawn into the passenger compartment to further improve the defogging and deicing performance.

If your vehicle happens to be in Dual mode, turning on the defroster will revert to driver control so both sides of the windshield will defrost evenly. Turn the driver’s side temperature to a setting that will best meet weather conditions.

For windshield deicing, your temperature selector should be turned to maximum heat and turn the fan speed to high.

As soon as possible, after the windshield is cleared, press the AUTO button to return to AUTO mode. The system will return to your previous settings. Pressing the DEFROSTER button a second time will also revert to AUTO mode.

To defrost or defog the rear window and, if so equipped, the outside mirrors, push the REAR WINDOW DEFROSTER switch. The indicator light will illuminate. After defrosting, push to turn OFF. If not turned OFF manually, this feature will automatically deactivate in 15 minutes.

There is a temperature sensor located on top of the dashboard near the windshield that helps regulate the automatic climate control settings. Please keep this area clear of papers and other materials.