Do what John suggests NOW.
Whatever it is, when it comes to engines :-).

Along the way you could try a poor-man's reverse flush .
One hose off - you work out which and where.
Thermostat out. .
Radiator cap off.
Air source. Lowis prom compressor easiest. See warnings at end.

Water fill radiator.
Apply air source to open hose / stand clear / ... fountain ...

Repeat until tender.

Fun even when  not effective.
Sometimes very effective.
Sometimes not.

Collecting effusant may provide some nice samples of stuff flushed from sys=
tem.

Do not:  destroy system with air pressure, destroy self with air
pressure, get perishable things wet, move rapidly and damage yourself
when fountain fountains (or slowly), spindle bend fold mutilate
staple,

YMMV.

Do what John says.
--=20
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