"An interesting proposition." Rokuro understands on a conceptual level, even if the chemical jargon goes almost entirely over his head. Force the trucks to stop innocuously by blocking the road with one of their number, and take advantage of the opportunity to investigate their contents.

"I do not know if I can manipulate this 'coolant' you speak of, as I have never encountered it, however... I could give the second or third driver what looks like a heart-attack, which may cause a similar delay and upset. As these things occur naturally in people, I doubt they would immediately suspect foul play or outside interference." It's not the most savoury of plans, but it may be the most reliable. Attempting to control the chemicals inside the vehicles, not knowing how Rokuro might affect them, is a risk.