1989 Johnson 4hp
 

I have a 4hp 1989 Johnson outboard used as an auxillary for a 15ft
Shetland
This has an impeller but I cannot see any tell tale pipe or water
inlet. Last season I had to use it in earnest to get me back and ran
it flat out for about one hour without it siezing so it must be
cooled. Could someone please explain this, also if there is a way of
connecting an external tank, mine has a small integral tank above the
motor which keeps needing replenishing
Thanks
Ali