Some older 240D's have a radiator cap and no expansion tank. The cap is at the highest point of the system. I still don't see the need to seal a funnel to the cap. Just fill it to the brim of the radiator or the expansion tank and as the engine warms and you rev the engine to create more flow, trapped air will rise to the cap and coolant level will drop and you just add more coolant. What am I missing? Why do unnecessary work drilling a hole in the cap which won't seal anyway unless you RTV it?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked