"Midlant" wrote:
Is the oil reservoir manually refilled periodically or is it an overflow
from the oil pump?

Don't know about small Mercurys but on large ones, the external tank
is supposed to keep the internal (under the cowling) tank full. Keep
the lids tight and hoses in good shape.

Now I need to know is the reservoir there in case the oil injection
fails

If the oil injection fails, the reservoir won't help matters.

or as a standby for the external oil tank?

IIRC, oil is pumped from the small (internal) tank to the mixer. The
small tank is simultaneously refilled by the large (external) tank.

It's been awhile since I've looked at the manual but I'm pretty sure
that's right. Theoretically, you shouldn't have to refill the
reservoir. Don't forget to check it frequently though (cuz $#!t
happens).

How do I know the oil injection system is working?

The warning horn is loud enough to wake the dead.

Rick