Keep adding until it's full. It's just going into the engine now is why it looks like the level stays the same. This is coolant mixed with water right? Sorry, can't tell you how much it holds.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k