Yamaha 20D Owner's Manual page 68

Oil level warning system
The various oil-level warning system functions are as follows:
Oil level warning indicator lamp
(Bottom cowling)
Red
Engine oil tank
more than 200 cm
OFF
0.181 Imp qt)
200 cm 3 or less (0.21 US qt, 0.181
ON
Imp qt)
O
3 (0.21 US qt,
2-21
Remarks
No refilling necessary.
Buzzer sounds in remote control
box and engine speed is limited
to about 2,000 r/min to help
conserve oil.
Check oil filter for clogging.
Add oil.
GB