Overheating at idle

[LAPLANT]

My 96 Merc XRI 150 is overheating at dle no water is coming out of the pee hle until around 1500 rpm
It doesn't overheat at all long as i keep it above 1500 rpm
I put a new impeller and pump housing in it
Thanks for the help in advance

[Chris]

Was the impeller installed right?

And did you get a complete waterpump kit with all the parts, or just the impeller alone?