WTF!? DSMs are sooo wierd.

The majority of you know that I have a blown headgasket(as far as I know). Well my car would start to overheat after driving like 3-4 miles. Then if I would put it in neutral or let off the gas it would cool back down fairly quickly. WELLLL, today somehow I managed to drive to and from work (52 miles) with out even peeping over my normal temp. I'm puzzled...