ORIGINAL: proptop
Well...
All I know is, back some time ago, (back in the early '80s ) a buddy and I were out cruzin' in his '67 Galaxie 500 convertable...hot summer night...and it over-heats...
It's night-time, and he goes to check the coolant level...takes off the radiator cap...can't see anything, so he whips out his cigarette lighter...
Whooosh![X(]
A jet of white-blue flame shoots straight past his face right to the under-side of the hood!
My guess would be yes, the fumes are flammable...
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Wow. That is the first time that I have ever heard of that happening. You're never too old to learn something new.