Volvo SX-M Raw Water Pump not pumping at 1700 RPM and greater

[billkoller]

1995 Volvo 5.8 EFI, New Raw Water Pump. Boat is in the water and the Gimbal water inlet is below the waterline by about 2". I placed a clear hose from the Pump out to the Vaporizer to check water flow at low RPM's the line is full of water at 1700 RPM and avoce there is more air in line than water. I took off the line from the Gimbal to the pump and pressure tested it, it passed, I replaced the Raw water pump and still have same results. There is no water at the Gimbal water inlet, with that much air I would assume I would see water if it were cracked.

Is it possible my exhaust is filling the water jacket of the outdrive causing it to sucking in as the pump starts moving at higher speeds?

Tomorrow I will be swapping the input hose from Gimbal to pump from one engine to the other. If that does not change I plan on adding running a long hose from the other motors Gimbal to this motor and vice versa to see how each motor reacts.

if anyone has any other ideas please let me know, I'm at a total loss.

 

[Senior B]

Was there an over heating problem before that still remains after the pump change or did you just put the clear hoses on and now perceive that you have a problem from the visual cues?

 

[Augoose]

I'm not sure I follow your troubleshooting steps. With the engine running, are you drawing ANY raw water into the thermostat housing? If you grab that cooling hose, do you feel water flowing inside? Do you suspect that you have a cracked hose in the outdrive and are drawing air?

 

[billkoller]

Was there an over heating problem before that still remains after the pump change or did you just put the clear hoses on and now perceive that you have a problem from the visual cues?

The clear hose was put on after repeated overheating to make sure the engine was getting the proper amount of water ( It gets full flow of water until around 1700 RPM then the line starts to dry up) the raw water pump was swapped with pump from other motor and the results didn't change. This tells me it's a water feed issue and not the pump.

 

[billkoller]

I'm not sure I follow your troubleshooting steps. With the engine running, are you drawing ANY raw water into the thermostat housing? If you grab that cooling hose, do you feel water flowing inside? Do you suspect that you have a cracked hose in the outdrive and are drawing air?

Yes with engine running below 1700 RPM I have full water flow feeding the thermostat housing. At 1700 RPM the line feeding the housing starts to dry up, the pup was swapped out and the results did not change. The boat is in the water and hose in the outdrive is totally submerged so even if cracked seems impossible for it to be bringing air into the mix.

 

[billkoller]

A little update for anyone with the same issue. I was correct the exhaust was getting into the water jacket of the outdrive causing the cavity to dry up. Turns out the seal on the pickup tube was not sealing correctly.