Raw Water Pump Priming

[w88dm4n]

Excellent forum.


My raw water pump now seems to require running the engine at 2500 rpm for 30 sec to regain its prime after more than an hour of not running. The problem began just after I replaced the impeller. So, I naturally re-seated the gasket but the problem didn't go away. So, I tightened the impeller housing screws and evey hose clamp I could reach while on the water. No dice.

Any ideas?

2007 Volvo 5.7Gi-300-J, 780 hours, pretty clean looking.

Thanks,

Rick

 

[Bt Doctur]

wrong impeller if it all worked before

 

[bruceb58]

Pretty hard for these to lose prime since the water level is above the pump. You are testing this in the water I assume?

You have an air leak somewhere.

 

[w88dm4n]

Yup, the problem is on the water. I'm assuming this is a priming problem. If running in neutral at 2500 rpm for 30 seconds pulls the temperature down that much, it's the only cause that makes sense.

 

[bruceb58]

Remove the 1" hose going to the thermostat that comes from the raw water pump. Start the engine and see how much water comes out when you have your engine running at 1000RPM.

At what temp is it getting up to and what does it go down to?

Did you you replace the impeller with an OEM Volvo impeller or an aftermarket part?

 

[w88dm4n]

I should explain. After putting in and going through the no wake zone, I normally run at 1200 RPM to the middle of the cove, then I open it up to get on plane. After that impeller change, I see 175F and thermal protect is the next stop. Puttig it in neutral at running to 2500rpm brings the temp down quickly.

Volvo impellor. I spend the extra money on all Volvo parts and do my own labor. I do run Sierra oil, though.

 

[dypcdiver]

Could be several things, I experianced something similar, I pressure tested after removing the outdrive and all held without leaking. I put clear hoses T'stat to Exhaust manifold and could only get flow at 2000 RPM plus. Turned out to be the bronze pickup tube between the upper and lower units. It is located in the exhaust tract and had burnt through and was sucking exhaust gas rather than water. New ones are stainless, I wonder why!

 

[w88dm4n]

Nice idea.. I took your suggestion and disconnected the 1" line. Running at 600 rpm, the volume of the hose was slowly pushed out, and the line was dry for the next minute. Also, the impeller gasket was mashed outside the seat and is likely the source of sucking air. Will re-seat and torque it this week. Feeling pretty foolish right now.

 

[PaulinSWFL]

Could be several things, I experianced something similar, I pressure tested after removing the outdrive and all held without leaking. I put clear hoses T'stat to Exhaust manifold and could only get flow at 2000 RPM plus. Turned out to be the bronze pickup tube between the upper and lower units. It is located in the exhaust tract and had burnt through and was sucking exhaust gas rather than water. New ones are stainless, I wonder why!

WOW. That's a great find. I'm commenting because of the issues I am having with a 5.0FL Volvo Penta.

 

[Lubak572]

Could also be the raw water housing itself being worn. I will be replacing mine on one of my engines.

 

[PaulinSWFL]

Could also be the raw water housing itself being worn. I will be replacing mine on one of my engines.

That's a definite for me too. I replaced the impeller after a overheat and it now has a slow drip from underneath. No gasket material on either piece of the raw water pump and it's only three bolts. Warped from the heat I guess.

 

[Grub54891]

Had one at the shop that did that. Owner did everything mentioned, Still had issues. After looking at myself and scratching my head, a new housing fixed it.