Quote:
Originally Posted by FL&WVMIKE
GM .........................
Most of these engines still have foundry sand in them, from day one.
I don't believe it is possible to have perfectly clean internals, in the cooling system.
When my mishap happened, it was not too long since I had given my engine the vinegar treatment.
It doesn't take much to clog that small opening.
MIKE  (mikeburch)
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There are thousands of these valves in use with very few problems. It's very simple to rinse them out once a year for the benefit they produce. I believe the instructions tell you to rinse them. After all these years there is very little or no sand being circulated. Any sand lays down along the pan rail and stays there unless it is dug out. G.M.