Originally Posted by paulri
I called Techron's support line a few months ago, and the guy told me that it didn't matter (when during the OCI to run the cleaner). I have read as much in threads on here, on the same question.
It was a long time ago, but way back when Chevron had a recommendation that the best time to us Techron Concentrate would be right before an oil change. The rationale was that the high detergent content could get into the oil and deplete some of the oil additives. I suppose the idea was to have a fairly short time where the additives were artificially depleted. They didn't really explain it though. A lot could have changed, including what went into the bottle as well as the additives used in motor oil.