I dont think thats true. Any fan that has had any kind of misshandling will vibrate badly. And will cause stress to the blades and rivets that hold the blades on the center spider. The fact that the fan is attached to something heavy and solid such as an engine and wont make you notuce is out of balance doesnt mean its ok!!!

If not just watch how any hosehold fan will vibrate to destruction when you mes just ever slightly with any of the blades.

An unbalanced fan will mess up your water pump a lot faster. Not to mention it can come apart while in operation and mess your car bad....or even worde kill you.

I will balance mine even if it takes to put a non original rivet here and there on the blades.

I just dont trust a fan that has been kicked around amd tossed in storage for 40 years!