1988 mercruiser checy 350 5.7L help it's over heating need advice

[animalpals2]

Motor has been running perfectly took it out this morning to go fishing and with in 20 minutes it started smoking and over heated to the max.
In spring we put a new impeller in outdrive, it was making like a power steering hissing sound at intervals this week, now it has a rattle sound in the outdrive when you rev it up. Does anyone know what the cause maybe that is making it overheat besides water pump or thermostat? The boat is a 1988 bayliner 25ft convertible 2556 cruiser. Thanks...

 

[Bondo]

In spring we put a new impeller in outer drive,

Ayuh,.... Welcome Aboard,.... Head back to the impeller, 'n see what's up with it,....

Then follow the water system forward,.... impeller, drive housin', transom housin' plumbin', the t-stat,...

If the boat is still in the water, pull the hose off the t-stat housin' that comes from the drive, 'n start it up,...
There oughta be 'bout 5" of water bubblin' straight up from the hose end,....
If there ain't, go to the impeller,...
If there is, check the t-stat, 'n motor plumbin',...

 

[animalpals2]

Ayuh,.... Welcome Aboard,.... Head back to the impeller, 'n see what's up with it,....

Then follow the water system forward,.... impeller, drive housin', transom housin' plumbin', the t-stat,...

If the boat is still in the water, pull the hose off the t-stat housin' that comes from the drive, 'n start it up,...
There oughta be 'bout 5" of water bubblin' straight up from the hose end,....
If there ain't, go to the impeller,...
If there is, check the t-stat, 'n motor plumbin',...

Thanks so much I'll update on Monday were having marina bring out of water so we can do a thorough check.

 

[Scott Danforth]

The raw water impeller will fill a 5 gallon bucket in about 20 seconds with the motor at 1000 rpm

Also, if the old impeller had lost any pieces, you have to find them