I'd still recommend the standard (methyl alcohol) version of Heet:
1) Iso-Heet is slightly more expensive ($2.29 vs $1.79)
2) Regular Heet (methanol) has much better anti-freeze properties:
An 80% solution of isopropyl alcohol freezes at -35.
An 80% solution of methyl alcohol freezes at an unbelievable -225.
3) I'm guessing that today's auto finishes are extremely resistant to
both types of alcohol-water mixtures. Years ago I was extremely
careful about using any solvent on an auto finish. I now use a
variety of strong solvents for difficult tar and bug removal - this
includes nastier solvents such as methanol and acetone. Decades
ago these could have ruined the paint. Obviously, you always
have to test the solvent on a small, hidden bit of paint first.


My reasoning on why methanol is used in the WWF that we purchase:
1) The extremely lower freezing points.
2) Paint finishes are much tougher these days. Some of the
binary formulations are rock hard.
3) Commercial methanol is about 3-4 times less expensive.
And since only half as much is need for the same anti-freeze level,
it becomes 6-8 times less expensive when used in WWF mixes.
4) Possibly, methanol is a better solvent for bug removal, etc.
I'm just guessing on this one.

Gideon