2003 Volvo Penta 5.0 GXI-D (SX outdrive) Cooling issue at idle

[GreggoryS]

My VP 5.0 GXI-D SX impeller will not provide cooling water flow at idle in the water and on muffs. It cools appropriately with the garden hose attached to the engine flush connection. I recently changed the seawater impeller and impeller housing. This is a new situation to me as I did not have this issue before the impeller change. At idle RPM (600-800 RPM) impeller will not pull water to cool itself resulting in elevated engine temps and eventually engine alarm. If I increase RPM to around 2000 RPM the impeller is capable of pulling water to sufficiently cool.
Background info: Lower unit was changed last year. I ran it 4 times after the lower unit change with no issues. All connections are tight and impeller housing is torqued appropriately. My thoughts are I have an air leak somewhere between the outdrive water pick up and the impeller. Any info as to where to investigate next would be greatly appreciated.
Thank you in advance. Cheers!

 

[Scott Danforth]

check the water inlet casting where the hose attaches to the outdrive. the fitting could be corroded and leaking (sucking air)

 

[Lou C]

On the SX you don't have that fitting that corrodes on the AQ Swedish style drives but there is the plastic fitting in the transom mount that can crack and pull in air (same as on an OMC Cobra, may even be the same part). When the impeller was replaced was the wear plate checked? If this gets scored then even a new impeller won't pump well.

 

[vwbugman69]

Did you replace the old oring from the impeller housing? I struggled for two seasons of the pump not priming until I found it. It would only prime if I reved the engine to 2k rpm.

My raw pump saga for reference

 

[GreggoryS]

When I replaced the impeller initially, I thought it was a pump housing issue and replaced the housing as well. This didn't correct the issue. Where is the wear plate? Also, I did change the pump housing O-ring and made sure it was seeded properly before tightening. Thank you very much of the replies.

 

[GreggoryS]

I did not replace the impeller shaft seal. It didn't look bad. Have a new one on hand, but thinking probably should throw it on for trouble shooting purposes. Digging that seal out looks like fun. Thx

 

[Silverbullet555]

Some things I did to troubleshoot flow issues.

Inserted clear hoses in all water lines so I could see flow and look for lackthereof and air bubbles. I used clear hose from lowes and brass couplers/reducers to make it work. Had to rig it up, but it worked.

Pulled water from a bucket, bypassing the drive and PS cooler to see if that helped the situation. Disconnect the inlet hose from raw water pump and connect another hose to that and run it to a bucket fill with water and keep it full. If it pulls fine in that situation you know your issue is in between the outdrive and raw water pump. Repeat behind PS cooler if necessary to eliminate the PS cooler and hoses.

DOn't forget to backflush the coolest and drive to make sure there is nothing clogging any of them.

If you replaced the entire raw water pump, which I did as well, the wear plate was replaced as well. If the water pump isn't dripping the back seal is likely fine and I would look elsewhere first.