How to Check the Compression on an Aircooled Volkswagen (Vw) Beetle

Compression is a measurement of the pressure that builds up within a cylinder as the piston rises and both valves are closed. For the fuel mixture to burn properly a certain range of pressure is required.


  1. 1
    Assemble the required tools:
    • Compression tester
    • A 13/16-inch spark plug socket.
    • A ratchet (3/8-inch drive).
    • A 3-inch extension, 3/8-inch drive to reach cylinders #1 and #3.
    • A universal, 3/8-inch drive.
    • A 6-inch length of rubber breather hose, 1/2-inch ID.
  2. 2
    Let the VW idle until the engine is completely warmed up.
  3. 3
    Turn off the engine and remove the spark plug connectors from each spark plug.
    • Mark each wire with masking tape so you can put them back on the correct plugs later.
  4. 4
    Remove all the spark plugs and block the carburetor throttle so that it is fully opened.
  5. 5
    Thread the compression gauge into a cylinder making sure that the pressure release button has been pushed and the reading is at 0.
  6. 6
    Crank the engine for about 2 seconds and write down the highest reading from the gauge.
    • Be sure to turn the engine over six to eight times, same for each cylinder.
    • It is helpful to have a friend who can crank the engine.
    • Compression readings should be high compression (over 100 pounds) and relatively uniform among the cylinders (within 5 pounds). Variations from cylinder to cylinder should be no more than 14 to 20 pounds.
  7. 7
    Recheck cylinders with low compression readings by injecting approximately 10cc of engine oil into the cylinder through the spark plug hole.
    • If the compression reading increases a little, the problem is probably worn, broken, or poorly seated piston rings.
    • If the compression reading remains the same, leaking or damaged valves may be at fault.
  8. 8
    Return the spark plugs.
    • Use the 6" rubber breather hose as an extension to hand-thread the plug into its hole.
    • Turn the spark plug a turn or so to ensure it is not cross threaded.
  9. 9
    Reattached the spark plug wires.


  • Safety should always be your #1 focus when working on a vehicle. ABSOLUTELY NOTHING in this world is so important, that you should EVER practice unsafe maintenance on your vehicles. Always use the proper tools for the job at hand. Common sense is a VERY IMPORTANT. I try to ensure the pages I add are error-free; however, I am human and make mistakes.

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Categories: Car Maintenance and Repair