Water pump install
 

I have a 150 Mercury 1988
And why do they say you should keep it in forward gear?
I always do but it always clips back to neutral.
I get it lined up by turning the flywheel but the Manuel says keep it in forward gear,why?

i was told to put it in reverse. Not sure it matters, just helps keep the shift shaft aligned when you put the foot back on.

When you spin the flywheel, you re lining up the CS with the driveshaft coupler.

you keep it in forward to keep the shift shaft in alignment. It allows you to turn the driveshaft with the prop to align the splines. On an I/O you cant pull teh drive without it being in FWD gear