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Old 13-12-2009, 10:40   #61
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Originally Posted by Jud View Post
I got less than even the lowest spec --lower than 4.5 gpm with a new impeller, so something's up. This was measurement directly from the pump.

I will check at the exhaust elbow hose connection tomorrow. But it's looking strongly like the pump is weak (and there are no problems on the suction side or barnacles, etc. fouling through-hull, etc. I've looked at everything upstream of the pump, including sea strainer, hoses, and through-hull intake (and transmission, which is sea-water cooled --sea waters passes through tranny after entering boat and before going to pump)
If the output directly from the pump is low and the pulley system is not slipping or changed for some reason, there is no other possibility than either a worn pump or a restriction of some kind on the inlet side.
Kinked hose when installed? Growth inside a hose?

We had a similar mystery with our Lord Nelson 35.
It took forever to fill the diesel tank, about 1 gallon a minute was all it would accept. We thought we had figured it out when we found a slight kink in the fill hose, but that was not it. When I cut open the hose to install a 90 degree elbow, I found the culprit. The inside of the hose had delaminated into a flower petal shape. The cross sectional area was near NOTHING. Replacement of the hose with a USA made brand solved the problem. The broker was very happy to hear of our discovery, as all Lord Nelsons were having the same problem and nobody had yet figured it out.

"I have never understood why it is "greed" to want to keep the money you have earned,
but not greed to want to take somebody else's money"

-Thomas Sowell
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Old 13-12-2009, 12:17   #62
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We have a 2003 which also used to have overheating problems. Ours occurred closer to 2500 after being run for a few hours. Over the course of correcting the problem we discovered:

1. A mass of muscles underneath the strainer. We have since removed the strainer.

2. 50/50 Polypropelyene mix was too thick. It was reduced to 60/40.

3. Not all impellers are created equal. The blue run dry Globe 1112 impeller was incapable of maintaining proper flow. This was replaced in favor the correct sized Jabsco.

We have now motored over 32 hours straight at 2500 several times without overheating.

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Old 13-12-2009, 13:54   #63
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Originally Posted by Paul L View Post
Where are you measuring the RPM. Is the pump geared 1-to-1 with the tach?

Paul L
Hey Paul --small world ;-)

According to the guy I spoke to at Johnson, the pump is directly geared, which means engine RPMs = pump RPMs, right... I'd forgotten about that --so, given the 4.25 gpm output I measured (@2500, which is supposed to be max. output; specs say it should put out between 4.5 and 5.4 gpm), it appears low. Since it is direct gearing, this seems to be further evidence to suggest the pump is in fact weak.

I'm bringing it to a specialty marine pump place to look over tomorrow. After all this, I feel like I've done my part .
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Old 13-12-2009, 14:03   #64
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Originally Posted by Chief Engineer View Post
I belive you mentioned you have a speedseal plate.....Is there a possibility that the gasket/o-ring is damaged?

From what I have gleaned so looks like the pump.....

There may be a leak at seal, lipseal (inside pump) this could be allowing air in at higher RPM......and while we are at it, take a look at the gasket on your stainer.....

BTW where are you located?
Might be the Speedseal o-ring...I don't know how to ascertain. It stands proud of the inside of the plate very, very slightly, presumably to form a seal.

You've made me realize I should ask the pump shop to test output with the Speedseal plate and with a stock pump plate to see if there's any difference in output. I have checked sea strainer gasket...thanks.

I'm in Vancouver, Canada (and there are plenty of marine specialty businesses here, fortunately.)
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Old 13-12-2009, 14:14   #65
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Originally Posted by Highlander40 View Post
The pump parts wear. Side plates and the radial cam that flexes the rubber. Even with a new impeller, excessive wear on the metal parts will cause bypass leakage. The bearing may go also and reduce the impeller deflection= less volume.

Maybe new pump time.
Thanks for the info, fills in the gaps in knowledge in my head...I had no idea these pumps could wear like that in various places.

I'll have the pump assessed and am thinking I'll probably just spring for a new pump for $150 instead of rebuilding (thanks for the info on pump source, PaulL).
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Old 29-03-2010, 20:06   #66
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Hey Jud, I have been reading this post for the last half hour and the suspense is killing me. Please reply and let us know if you fixed the overhating problem!
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Old 29-03-2010, 20:18   #67
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Overheating and Raw Water Flow Specs - 28hp Volvo

Originally Posted by SailingYoungs View Post
Hey Jud, I have been reading this post for the last half hour and the suspense is killing me. Please reply and let us know if you fixed the overhating problem!
Hi --No, unfortunately, I never solved the problem.

Not for lack of great advice --I got tons of it here! But for lack of time. For various reasons (life is busy!), I never had sufficient time to try various things, and now the boat has been hauled and will be on the hard for a while, making it impossible to diagnose the overheating (until it's back in the water).

One thing: I did change the pump's wear plate (back of the pump), and cam, and smoothed out the groove worn in the front of the cover (Speedseal cover). Ran the boat the other day, and even after these things, the engine still starts to overheat over 1900 RPMs. So, the engine overheating fix will have to wait until the boat's back in the water.

Thanks again to everyone for all the great advice.

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Old 29-03-2010, 20:43   #68
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If you haven't already replaced the might have this problem. If the center brass piece has come loose from the rubber (bond). It may work a low speed, but spin inside the impeller at higher speed. I have seen this an a few rare occasions
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Old 29-03-2010, 21:02   #69
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Since you probably know such things.... the OP's 4.5 gallons a minute seems like quite a bit of water to me. I'm always happy to see a "nice flow" of water coming out - but never thought to measure how much. Sort of like flow from a more personal piece of equipment

When engine manufacturers do a spec for this sort of thing, is it theoretical (e.g. at the mixer) or is it the gallons per minute at the transom after the water's gone through the waterlift muffler, risers, etc. (e.g. is it like those imaginary bilge pump GPH numbers )?

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Old 29-03-2010, 21:12   #70
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when you changed the raditor fluid what mix did you use? too much fluid and not enough water will cause low heat transfers.

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overheating, raw water, volvo

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