Stone hit radiator

But years of the small ones flattening the radiator fins did block much of the airflow in one of my past cars, so I have put screens in later cars to stop even them.

 

I've put cardboard in front of the radiator when the temperatures dip far below zero, like everyone else who lives in these sub-arctic regions, and I have also forgotten to take them off when it gets warm. Yes, the electric fan compensates to a large degree for the lack of airflow by sucking air through the rad (provided you had the good sense to leave a space between the cardboard and the rad) but it consumes a lot of power, and when it gets very warm, it can't keep up, and you get a radiator blow-out, which is bad news all around.

Would I risk blocking off the air vents permanently, even here in Canada?
Not a chance.

 

Unless OP tailgates like my daughter does.

If it were me, and I'm a redneck DIYer, I'd go to the hardware store and get some hardware cloth to afix in front of the radiators. And I don't tailgate.

 

Same here, even with several -20C days this past winter I don't bother with grille blocking. I would end up forgetting about the grille block anyway...oops

Wow though sucks about your radiator getting stoned

 

I still have the lower opening blocked from two winters ago. I left it blocked and watched all the temps last summer, with none causing me any great concern.