GENERAL METHOD DESCRIPTION
THE CYLINDERS CAN BE CHECKED FOR LEAKAGE AS AN ALTERNATIVE TO A COMPRESSION TEST
Scheme 93
Using this method, the amount of leakage at the engine cylinders is measured and it is possible to locate the source of any leaks.
A similar check can be performed using a compression gauge by injecting oil in the cylinder. However, this can cause a build-up of coke!
The result will not always be decisive or precise.
In addition, the VIDA station or the Volvo System Tester (VST) must always be connected afterwards to erase any diagnostic trouble codes (DTCs).
HOW IS THE CYLINDER CHECKED FOR LEAKAGE?
- The engine should be run to operating temperature so that the thermostat is open
- The piston in the cylinder that is being checked must be set to top dead centre (TDC) at the compression phase
- A metered air pressure is connected to the relevant cylinder via an adapter that is secured in the spark plug / glow plug well
- A gauge is used to measure the size of the leakage from the cylinder. This is a pressure sensor with a regulator and displays the size of the leak expressed as a percentage. This allows the extent of any problem to be determined.
FAULT-TRACING
The source of a leak can be located by analysing sound at the following points.
| Exhaust pipe | Faulty exhaust valve |
|---|---|
| Intake manifold / throttle body (TB) | Faulty intake valve |
| Dip stick hole / Crankcase ventilation | Faulty piston / piston ring |
| Adjacent cylinder | Faulty cylinder head gasket |
| Radiator | Faulty cylinder head gasket / cracked cylinder wall. Also check for bubbles in the expansion tank. |
A mechanic's stethoscope or a rubber hose can be used as a listening device.
Note. There is leakage at the piston rings even on a perfect engine. This is the only place where a small leak is permissible.
CHECK
If a leak is detected that is assumed to come from the valve system, first check that the piston in the relevant cylinder is at top dead centre (TDC).
Then try to set the piston just prior to top dead centre (TDC) and redo the test.
When repeating the leak test on the same engine, there are usually variations in the results of the measurements.
This is due to changes in the engine coolant temperature (ECT) and the piston not reaching the same position as in the previous test, and is affected by the amount of oil on the piston rings at the time.
OTHER INFORMATION
Use: see 9512775.