There are relatively cheap testers that can detect combustion products in the coolant system. I had one and it worked really well. You can get them from NAPA.
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Don't bother giving me "rep", I won't return it and I think it is stupid.
Gracie Barra Clearwater
Gyms in Clearwater, St. Pete and Port Richey
pm me if you are interested in trying a free class at any of the gyms.