Optimistic Paranoid
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SternWake said:. . . No issues with heater core clogging either, but this is certainly a consideration.
Heater cores have to be scrupulously clean before you use a stop leak. IIRC from my days of selling auto parts 20 years ago, any good stop leak will plug any hole smaller than .035. The tubes in heater cores used to only be .040 when new - at least back in the old days, I couldn't say if that changed when they went to these new aluminum radiators you were mentioning. Anyway, it's scale build up in the heater core that causes it to plug when you add stop leak.
If it does happen, you want to get the hoses off the core and MacGyver a garden hose to flow through it in reverse. That will blow the plug out and restore heater functionality.
It's easy, btw, to tell which way is reverse. Normal flow is always from the water pump, to the heater core, and from the heater core back to the engine.
Regards
John