I blew a head gasket in my taurus once. You will know if it happens. It's a cloud of white smoke and it smells sweet.
Do you have aftermarket tailpipes or anything? mine are set kinda wierd and slanted up a little, not by choice they just fit wierd. Anyways, when I wash the car water collects in the pipes. I know you said you didn't wash it, cut could it be condensation from sitting overnight and being cold? Just a guess.
i was havin the same prob w/ my 2000 GT. but it was also leakin coolant up front. i had a crack in the intake manifold, it also leaked into one of the cylinders which then made the engine light go on.