JRC JMA-5206 Instruction Manual page 298

(1) Radiator
Attention
If the radiator front face (radiation plane) is soiled
with smoke, salt, dust, paint or birds' droppings,
wipe it with a piece of soft cloth wetted with alcohol
or water and try to keep it clean at all times.
Otherwise, radar beam radiation may attenuate or
reflect on it, resulting in deterioration of radar
performance.
Never use solvents of gasoline, benzine,
trichloroethylene and ketone for cleaning.
Otherwise, the radiation plane may deteriorate.
Check up and clean the radiator.
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