Immediately after an oil change, one of the things that confuse, and many professional mechanics or people who make their own oil changes face, is the lack of oil pressure during engine start. Although not a common occurrence, it is likely that the pump has trapped air in the suction side (which in terms of fluid mechanics is known as loss of prime) during the oil change.

When used motor oil is drained, the suction pipe can possibly be empty and the pump itself. When the new oil is added, the suction pipe which is normally submerged is filled with air. Entrapped air causes cavitation and prevents the oil flow and the required pressure is established. The low pressure indicator light stays on or oil pressure gauge indicates very little pressure when the engine is started.

Many installers tend to blame the filter for this situation and assume that the filter is blocking the oil flow. Because of the suspicion of the filter, the installer will replace the filter with a new one. Sometimes this solves the problem because the trapped air was released when the first filter was removed. Of course, the installer suspicion that the first filter was clogged increases.

The point is that the filter was not the problem and, in many cases, the solution is simple.

If the low pressure warning light stays on, or the pressure gauge indicates little or no pressure after 30 seconds of starting the engine, turn it off. Loosen the oil filter until the gasket just touches the base of the motor. Disable the ignition system (disconnect the ignition coil) so that the engine does not start. Operate up to rotate the motor to see oil in the gasket. DO NOT OPERATE THE RUN FOR MORE THAN 30 SECONDS. After oil appears in the gasket, tighten the filter and wipe off the oil excess. Start the engine. The oil pressure should return to normal within ten seconds.

  1. If the above procedure fails, it is necessary to remove the filter and use an oilcan to add motor oil into the hole of the motor base which is adjacent the threaded pin where the filter is screwed filter. This will prime the pump.
  2. Subsequently, fill the filter with oil, install and tighten. The oil pressure should return to normal within ten seconds after starting the engine.
  3. Filling the crankcase with oil immediately after draining the used oil will prevent trapping air in the pump suction line.
  4. Also, make sure the filter is installed correctly. Installation instructions will be in the filter itself or in the packing box.