I need to put some water/anti-freeze in my radiator to top it off, should I go do it while it's hot or wait till it cools down? And why?

 

I would say if you need to add to your radiator, then you must do it while it is cold. If you take the radiator cap off when hot, its under pressure and could burn you. Do you have your coolant overflow tank? if so, then just make sure that is at the full mark when hot, if its low, fill that while hot.

 

You are correct, I was doing some research on this and found this link
coolant level check

I know to open the radiator cap slowly to avoid being burned, but it says adding cool coolant to a hot radiator could cause it to crack. I should have known this:doh:

 

I was actually going to tell you to do this just because it woulda been funny when it cracked and you got pissed at me :rofl:

But really, there are warnings on the cap that tell you to not take off when hot

 

Yeah, take it off while hot and it really sprays. I was around when my mechanic uncle had to unscrew one, and I was glad I wasn't doing it, even tho he did have a cloth. And I add my coolant to the reservoir while it's cool, since it has two reference markings.