....and I did just a little while ago. Even in this heat, the mods made it run cooler. LOL Normally, it rarely went to that first mark, which is about 1/4 the way up. Now it splits the difference at about 1/8 the way. That was with plain water. My experience is they cool a little better yet with coolant. I didn't want to add coolant right away, in case the radiator had a leak. It does not and holds pressure well.