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...
My friend seeked after the problem with coolant leagake around in the engine room in Volvo 450, he saw in the coolant expansion tank with pocket lighter, whooom!!! His hair burned and all was well. Cause there was gasoline in coolant from defect cylinderhead gasket.
Jens Eirik