As I recall the JT3D engines, we used to apply fuel heat at a regular time (30 minutes?) for 1 minute when the #1M tank temp was below a given temp. Tank #1M was the only one with a temp sensor. We also used to apply 1 minute of fuel heat if the fuel icing light illuminated for any engine.
I apologise if I've got it all mixed up, I last flew B707 as FEO in 1977.