[JFP in PA]

I'd suggest against adding any other coolant to the OEM stuff; we have seen too many episodes of gellation issues for it to be worth the risk of spending a lot of money if the system cruds up (we handle them on a strict "time and materials"basis, and none of them have been cheap). The OEM stuff is available, not that expensive, does a good job, and holds up well for a long time (when mixed with distilled water). Yes, there are products that will mix with the OEM stuff and not cause problems, but there appears to be several that won't; mixing them is akin to tap dancing in mine field. You might get lucky, or you might not............