I used to operate L-1011s from the Caribbean to LHR, where the aircraft turned around in about 2 hrs. No smoke on summertime starts at LHR, but every once in a while when it was really cold at LHR,there would be a cloud of smoke that smelled strongly of kerosene. Noticed it with other operators too. Also operated to YYZ where it was colder, but not as many "smokers". Beats me!