Kia Optima Hybrid Owner's Manual Quiz
Engine Mechanical System

Compression Test

In this manual: Engine Mechanical System
General Information — 4Engine Mechanical System — 50Engine Electrical System — 20Emission Control System — 30Engine Control System/Fuel System — 84Automatic Transmission — 98Drive Shaft and Axle — 15Suspension System — 36Steering — 12Restraints — 50Brake System — 38Body (Interior and Exterior) — 54Body Electrical System — 233Heating, Ventilation, and Air Conditioning — 57
11steps
~66min
3/5difficulty
010203040505.94N·mlb·ft
Tightening torque found on this page
Done 0 of 11

Compression Pressure Test
If engine power is insufficient, oil consumption is excessive, or fuel economy is poor, measure the compression pressure.
The engine may start at any time when the vehicle is in READY mode. 1. Warm up and stop the engine.
  1. Warm up and stop the engine. Allow the engine to warm up to normal operating temperature.
  2. Remove the engine cover.
  3. Disconnect the injector connectors (A).
  4. Disconnect the ignition coil connectors (A).
  5. Remove the ignition coils (A).
  6. Remove the spark plugs. Using a 16 mm spark plug socket, remove the 4 spark plugs.
  7. Check the compression pressure in the cylinder.
    1. Insert the compression gauge into the spark plug hole. If possible, position the gauge so that it can be seen from inside the vehicle.
    2. Connect GDS
      • Connect the GDS cable to the data link connector.
      • Select the vehicle model, then select the HCU system.
      • Select "Engine On Test". Refer to the screens below.
    3. While cranking the engine, measure the compression pressure.
      • With the brake pedal depressed, press the Start/Stop Button (SSB) once.
      • If the engine starts, crank it for 8 to 10 cycles (until the gauge readings stabilize), then press the SSB once to stop cranking.
      • If the engine does not crank by itself when the SSB is pressed, use GDS to crank the engine. In "Engine On Test", follow the on-screen instructions.
      • "Engine On Test" will start cranking. After the compression readings stabilize (8 to 10 cycles), press the SSB once to stop cranking.
    4. Repeat steps (1) through (3) for each cylinder.
      Make sure the ignition is OFF between each cylinder check. This measurement must be performed while the engine is still close to operating temperature.
      Compression pressure: 1283 kPa (13.0 kgf/cm², 185 psi) / 200 ~ 250 rpm. Minimum pressure: 1135 kPa (11.5 kgf/cm², 164 psi). Difference between cylinders: 100 kPa (1.0 kgf/cm², 15 psi) or less.
    5. If compression is low in one or more cylinders, pour a small amount of engine oil through the spark plug hole into the cylinder and repeat steps (1) through (3) for the cylinders with low compression.
      • If adding oil improves compression, the piston rings and/or cylinder bore are likely worn or damaged.
      • If pressure remains low, a valve may be sticking or seating improperly, or there may be leakage past the head gasket.
  8. Reinstall the spark plugs.
  9. Install the ignition coils.

    Tightening torque: 3.9 ~ 5.9 N·m

  10. Connect the injector connectors and the ignition coil connectors.
  11. Some DTCs may remain after the inspection test and may need to be cleared manually using GDS.

Test yourself

A quick Kia Optima Hybrid Owner's Manual quiz: every answer comes with an explanation and a link to the manual page.