GM straight 6 overheating

[west8586]

Just bought a 75 with the gm straight 6 (not sure what horsepower) . The motor was totally rebuilt and has 25 hours on it. Took it out and it immediately started to get hot. So I now have the out drive torn apart as it was not pumping water to the engine. I pulled the impeller and stuck a different one in it from a spare pump. I noticed right away the difference. The old one could easily be turned inside the pump by hand. The new impeller was very hard to turn. Could this indicate that the impeller was bad and this was my overheating issue?

 

[west8586]

Before I tore it apart, I did find that the thermostat was bad. Ran it without and it still got hot. Flushed all lined with pressure bladder just to ensure no blockages.

 

[southkogs]

Welcome aboard West:

75 OMC with an inline six should be a 165HP. Being easy to turn is a good indication that the impeller was bad, and a bad impeller will cause the system to overheat. I would recommend buying the service kit and putting a new impeller (not a used one) in. I would also recommend you grease your swivel bearing - that will keep exhaust gases from overheating your engine.

The impeller does sound like your problem, though.

 

[west8586]

Well, put a new impeller in, and still getting hot. But this time it's only at full throttle, cools fine from about half throttle down. I'm thinking I may have put the impeller in backwards? I made the mistake of not looking at which direction the old one was in, so I had to guess. Other than that it ran perfectly. Hoping it's as simple as flipping the impeller the other way!

 

[bruceb58]

Did you do what Soutkogs said and grease the swivel bearing?