Brief recap: Had started to notice a gradual overheating over a period of time.. First thought was that the impeller was failing. After replacing the impeller, there was an inability to get water to come out of the stern discharge. Replacing the cam did help, but lost the prime yesterday. Today: Removed the pump cap and lubed the impeller. Removed the thru hull seen line at the pump to prime, but it had water in it. Started the engine and was rewarded with discharge water..
Facts: 1986 Universal M25
Oberdorfer pump ( OEM?)
Heat exchanger caps dropped and clear sightline to port side
First new impeller failed, second holding strong
New cam installed
New intake hose and pump to exchanger installed
Oberdorfer pumps currently unavailable
Boat is propelled by an 3 bladed Autoprop
WOT yields 3000 RPM when not in gear
Normally the engine in forward WOT will only yield 2300 RPM and push the boat at 6.8 to 7.2 kts
NOW: Above 1900 RPM overheating will slowly start
1500 RPM yields 5.2 to 5.4 KTS
1900 RPM yields 5.8 to 6.2 Kts
CONCLUSIONS: Yesterday when the engine was hot and had lost the prime after checking the strainer and would not pump it was reasoned that the heat expansion of the pump body that is already believed to be out of tolerances that were exacerbated by the heat of the pump.
Today with a cold engine and no need to prime, the engine/pump was able to draw, pump and cool the engine. The replacement of the cam added significant area to the internal pump body that allowed it to perform. BUT, that alone is not enough when the engine is under load.
So for now, RPMs will be held below 2000 RPM...
Once Oberdorfer is back up and in production, a new pump will be acquired and installed. This might not happen until next spring, but an update will be provided.
Facts: 1986 Universal M25
Oberdorfer pump ( OEM?)
Heat exchanger caps dropped and clear sightline to port side
First new impeller failed, second holding strong
New cam installed
New intake hose and pump to exchanger installed
Oberdorfer pumps currently unavailable
Boat is propelled by an 3 bladed Autoprop
WOT yields 3000 RPM when not in gear
Normally the engine in forward WOT will only yield 2300 RPM and push the boat at 6.8 to 7.2 kts
NOW: Above 1900 RPM overheating will slowly start
1500 RPM yields 5.2 to 5.4 KTS
1900 RPM yields 5.8 to 6.2 Kts
CONCLUSIONS: Yesterday when the engine was hot and had lost the prime after checking the strainer and would not pump it was reasoned that the heat expansion of the pump body that is already believed to be out of tolerances that were exacerbated by the heat of the pump.
Today with a cold engine and no need to prime, the engine/pump was able to draw, pump and cool the engine. The replacement of the cam added significant area to the internal pump body that allowed it to perform. BUT, that alone is not enough when the engine is under load.
So for now, RPMs will be held below 2000 RPM...
Once Oberdorfer is back up and in production, a new pump will be acquired and installed. This might not happen until next spring, but an update will be provided.