there IS a pre-diluted version of finalcharge and it says so on the bottle... there is also a full strength version of final charge..
on the phone he told me that a maximum of 20% of 50/50 mix could be present of other coolants in the system when converting to finalcharge...
fleetcharge is a different makeup than finalcharge.. the bottles are totally different...
fleetcharge is pinkish purple in color..
finalcharge is red..
im talking the full strength bottles.. it will say on it if it is a 50/50 mix
it could be too that mixing the 2 makes it tough to test for proper amounts of the correct chemicals for the anti cavitation but that your engine is still protected...
im only going on what the engineer told me when I called .. my guess is there's likely other scenerios where the engine and cooling system are not at risk but that they dont recommend