Mercruiser 233 Overheating

[Ctmangrum]

My 1976 mercruiser 233 overheats at rpm when i run it with the plunger while its on the hard. Anyone else have that issue just when using the plunger? Just curious if its not getting enough water or if i have a more serious issue. Launching in 2 days so im committed. Thanks.

[Ctmangrum]

Meant to say higher RPM

[km1125]

My guess is that you're not able to feed it with enough water to satisfy the flow at higher RPM. You really shouldn't running it "at RPM" on a hose.

How old are your impellers? When was the last time you inspected/replaced them?

[Viper]

RPM is the key here. It doesn't take much above idle on a garden hose for you to starve the pump. The true test is how it runs in the water. If we're talking inboard here, the pump can be serviced in the water if you find it still overheats at higher rpm after launch.

[Ctmangrum]

Source of the post My guess is that you're not able to feed it with enough water to satisfy the flow at higher RPM. You really shouldn't running it "at RPM" on a hose.

Impellers are only a couple years old. Makes sense about the hose. Boat never had sea strainers so i wasn't sure what to expect. Appreciate it

How old are your impellers? When was the last time you inspected/replaced them?

[km1125]

Just as a comparison, the average hose running wide open is about 10 gallons per min(GPM). A long hose or any restrictions will cut into that quite a bit.

At idle a small block raw water pump could pump 5-10 GPM but at 2000 to 3000 RPM that could rise to 40-60GPM. You could easily starve the pump supplying it with just a hose.