There seem to be a lot dependencies to this. An iced windshield at 30 degrees F is a far, far cry from the same at 30 degrees F. From my experience, you can safely pour warmish hot (NOT boiling) water all over the 30 degree windshield with reckless abandon. I’ve got many dings and stars in my windshield, and never have come close to getting a crack from pouring the hot water to remove ice.
Now then – I am in Louisiana, and it’s uncommon to wake up to weather colder than the high twenties with ice on the windshield (the rare part is the temperature after sunrise being so low, not the presence of windshield ice). What happens much more often is that the overnight low will be something like 25-30 degrees F, but the morning drivetime temperature will have risen to about the mid thirties. Because of the humidity, ice commonly deposits on windshields in the dark of night, and is still there in the hour or two after sunrise. Perhaps if the ice is already slowly melting, it’s ever so much safer to our the hot water on it … maybe the ice isn’t “gripping” the windshield so tightly.
I use just slightly tepid water - not even really warm. I’ve never had any cracking problem, but we don’t get really cold weather here in southern England (lowest overnight mins are usually around 20F a few times a year).
If using tepid water, you need to leave the wipers going once the frost has melted, otherwise it will refreeze.
If we have to get ice off our windshields in New Orleans, they certainly have to in Alabama, as well. I’d expect northern Alabama to get quite cold, actually. Not Minnesota cold, but probably getting down around 10-12 F at some point every winter.
I am betting that as long as whatever you’re doing doesn’t vaporize the ice instantly, the risk of cracking is minimal. Also, there seems to be a sweet spot temperature-wise (circa 25-35 F) where gentle melting is possible without rapid re-freezing.
Okay, ahead and ordered the thing. I can’t help it. My name is mangeorge, and I am a gizmo addict.
So, I’ll install it and sound the alarm here if it cracks my windshield within the next couple years. If it works good, maybe I’l post my excitement in MPSIMS.
Bub Eye
mangeorge
