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Would it do any harm to OVER-fill (like nearly full) the antifreeze/coolant overflow/recovery/expansion tank (bottle)? What about concentrations of antifreeze/coolant of more than 70% - is that harmful??
Wont hurt anything to overfill your expansion tank, it will just leak out of the cap on the tank if it needs more room to expand.
If you have more than a 50/50 concentration of anti-freeze that itself wont hurt your truck but it does hurt how much heat your coolant can coolect and remove so your truck will run hotter and could over heat which will damage your engine. 50 percent anit-freeze is about the most you want to run.
I knew a guy once that ran about 80 percent anti-freeze and fried his Mustangs motor the first summer he drove it here in Arizona. Anti-freeze raises the boiling point and lowers the freezing point but it doesn't help your cooling system remove more heat.
50-50 is the recommended mix of Anti-Freeze to water. More water you risk freezing, less water you risk boil over. Variations from 50-50 are area dependent.
In Arizona, a bit more water can't hurt. In northern Maine you might want a little richer mix of antifreeze.
Here in the Midwest we generally do 50/50.
It's really not rocket science, but straight Ethylene Glycol coolant doesn't do a good job at either extreme by itself (or so I was taught).
IIRC, it can get slushy at around -10F and boil at about 220F straight from the bottle. It needs water to broaden the range of protection.