I fill mine on the bench, pull the rad hose out of the way and slip it in place pre-filled. Never been a prob spilling for me. Perhaps different engine bays fit together slightly differently.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)