Penta 5.0 GXI overheating

[Jojo28]

Last year we began to have an over heat issue at the end of the season. Few months ago, I changed out the impeller and snapped the mount hole on the raw water pump, so I replaced the raw water pump and impeller assembly. Cranked up and overheat still exists. Replaced the thermostat (it was pretty corroded and stuck) and no change. Disconnected the thermostat housing intake house at the impeller and found the impeller not sucking water. Filled the hose with water, reconnected, and cranked engine. Temperature dropped to within limits at about 160°. Ran the boat all day with no issues. Next time out, she overheated at the docks of before we could shove off. Performed another "prime" and temperature back to normal. This past weekend went to take the boat out for a third time and spent an hour and half trying to get the impeller to suck water. Seems like everytime the boat comes out the water, the next time she's in, she overheats. I checked and replaced all my packings and o-rings to the garden hose connector and impeller. Checked for any obstructions and blockages in my intake hoses with no issues. My wife winterized the engine with a coworker but couldn't remember all the plugs they pulled. My thoughts are I either have a bad aftermarket raw water pump and impeller or possibly an open plug somewhere. Any suggestions?

Boat is a 2007 Chaparral 236 SSX with a Volvo Penta 5.0 GXI.

 

[saaristo]

One possibility is that it sucks air somewhere...I would suspect the "garden hose" or flush connector. For a temporary testing, plug it wit something other than the original plug.
Other option is that I've heard before, some engines are incapable of selfpriming, meaning theres airbubble in the intake hose. Follow that its not squeezed somewhere in the back of the engine.
Third one, intake hose might have cracked near the transom assembly either inside or outside. As soon as you are on plane the boat lifts and the crack in the intake hose outside the boat starts sucking air. Seen that.

 

[dubs283]

My thoughts are I either have a bad aftermarket raw water pump and impeller or possibly an open plug somewhere. Any suggestions?

When it comes to rubber parts and electrical parts OEM is the only way to go. Hoses and starters/alternators are pretty decent aftermarket but fine parts like bellows, pumps, tune up parts, etc...aftermarket is not reliable

Have you checked for any leaks when the engine is running and cooling properly?

 

[QBhoy]

Hi, does this have a oil cooler on the line between the inner transom and water pump on engine pump ? down low on port side usually. These can be the cause of issues, when they are perished and drawing air

 

[BRICH1260]

I`d check the following. O ring seal on the water pump, Flush port cap not sealing properly, outdrive hose transition nipple broken or cracked.