A viscosity too low can cause cavitation and pump impeller damage.
Viscosity to high can cause high running current and motor damage.
>>A viscosity too low can cause cavitation and pump impeller damage.<<
I hate to show off, but pump cavitation is strictly a function of liquid vapor pressure at pumping temperature. Cavitation is NOT a function of viscosity. Sorry. Cavitation is associated with bubble formation and rapid collapse which is stricly a function of vapor pressure. Viscosity is generally associated with Reynolds number which, in turn determines pressure drop due to fluid flow. I say all this because I busted my ass as a young man studying this crap so much so that I neglected the love of my life and got painfully kicked to the curb which resulted in me carrying a huge hole in my heart. It was really not worth the effort.