Very sparingly.
If your engine is clean, I doubt that it is needed.
The only place I have used it is in an area behind the engine in the GTP that I can't get to to clean properly.
It may be a great product, I just don't happen to see much value in it for me.
I have had a few cans for close to two years and have used less than 1/4 of a can in that time. :dunno: