White smoke, but only when cornerning
 

I have a '78 280CE, 6 cylinder, double overhead cam, with 190,000 miles. After driving for 30+ miles on a straightaway at 55-60 mph, when I decelerate to make a 90-degree turn, an ENORMOUS cloud of white smoke blows out of the tailpipe, lasting for 8-10 seconds. After thoroughly embarrassing me, then it's fine until the next 30+ mile trip. If I drive in town at 30-40 mph for hundreds of miles, this never happens. Only after driving over 30 miles at speeds of 55+ and then turning does this happen. Any suggestions on what I can tell my mechanic to check out?