I have mixed up two loads of APC as directed. one is at 10:1 and the at 4:1. Now all it really says for use is use the weker solution for light use and 4:1 for heavy. If use the 4:1 in the engine bay is that going to be OK if I get overspray on belts or anything in there? i am going to use it inside as well on fabric and plastics. Is the best thing to do just test the mixes and check there is no reactions and proceed? I tried a little 10:1 on the carpet in the flat and it was awesome !