1973 Slickcraft 188 overheating

[ThirdCoastBoater]

hello everyone, I’m new to the site! I just purchased my first boat, 1973 Slickcraft w/ 188 mercruiser (Ford 302) with 888 drive. My issue is that my boat is overheating when going anywhere above idle. I have replaced thermostat, impeller, water pump, and back washed block lines. I have seen other similar posts however only info about overheating while going slow and mine seems to only overheat while going fast. I was wondering if anyone could suggest where to look next. Thank you in advance!!!

 

[achris]

Check exhaust elbows and manifolds. If they're partially blocked it reduces water flow and you overheat, only when you're going fast.

The other possibility is the water pocket cover in the drive.

Btw, your engine is an 888, and the drive is an MC-1... That '888' sticker on the drive is an 'engine designator'...

Chris...