04 Toyota 4Runner P0306 diagnosis video

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      My theory on the 4Runner is that the head has a fracture between a coolant passage and the intake valve chamber of the #4 cylinder. When you preformed the compression test their was no loss of compression as the fracture is small, for now and the intake valve closes rapidly sealing off the valve chamber enough to allow compression to build. When the leak down test was done, the intake valve was closed thus sealing off the fracture, so no loss of pressure.

      I believe when you did the smoke test, the intake valve in the #4 cylinder was closed. This allowed pressure to build in the intake valve chamber then push through the fracture and into the coolant.

      The leak down test, tested the head gasket. The intake smoke test, tested the valve chamber. Coolant bubbling was heard during the smoke test but not the leak down test.

      Research showed that the 04 Toyota V6 had issues with head gasket failures on #4 and #6 all of which had compression leaks.

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