I know for sure you can't have it too tight, I had mine too tight while back and broke it and had to take it to the shop to replace, so don't tighten it too hard.
Far as too loose, long as coolant don't come out then its not loose. Just keep tighten it until you fell like youre forcing it then stop, thats what I do.
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Exterior- stock painted black wheels, clear corners, stainless steel grill, cross and drilled front and rear rotors with evolution brake pads.
Coming soon- 18 inch black mustang bullet rims, GT/GTP rear bumper, tinted windows.