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Old 11-09-2015, 07:51   #1
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Perkins 4-108 Intermittent Raw Water Flow

Hello:

Intermittent raw water flow issue with Perkins 4-108:

Normally my engine has no water flow issues.

However, this year, I have gone to start the engine twice and had no raw water flow from the exhaust. Both times it happened after sailing (but only once was the boat healed over significantly). The first time I stopped and restarted the engine several times before it finally had good flow the last time. During the episode I even dove under the boat to make sure that nothing was blocking the intake. Yesterday - after a relatively flat sail it did it again. However, this time I had good flow following the first restart. The strainer is clear and I change my impellor every year even if I don't need it. When the engine has flow it runs perfectly and has normal temperature.

Does anyone know what might be causing these intermittent flow issues????

Thanks in advance for any input you may have.
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Old 11-09-2015, 08:17   #2
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Re: Perkins 4-108 Intermittent Raw Water Flow

We had a bout of that problem and it was the impeller. There were backward vanes.
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Old 11-09-2015, 09:40   #3
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Re: Perkins 4-108 Intermittent Raw Water Flow

It could be that the inside of the pump is too worn to prime--if the cover plate has significant wear, turn it over.
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Old 11-09-2015, 09:56   #4
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Re: Perkins 4-108 Intermittent Raw Water Flow

or possibly you have the wrong impellor... a bit small? You have to be careful about some of the "interchangeability" of impellors on line.
Trying to remember how that engine is plumbed... is there any way the raw water could drain from the system when not in use...?
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Old 11-09-2015, 10:46   #5
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Re: Perkins 4-108 Intermittent Raw Water Flow

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Originally Posted by donradcliffe View Post
It could be that the inside of the pump is too worn to prime-.
The cam in the Jabsco pump wears but is replaceable, maybe invest in a raw water pump rebuilt kit.

Also, I have bought a bad batch of impellors once that lasted about a month before they started shedding vanes

Jabsco parts are cheaper than Perkins
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Old 11-09-2015, 11:05   #6
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Re: Perkins 4-108 Intermittent Raw Water Flow

Could be any of the pump problems previously listed. How old are the lines between the intake and the pump? Anywhere air can get in has the potential to cause problems. Loose clamps, delaminated hose, brittle strainer seal rings all need to be checked for too. Should be a fairly simple process of elimination, since system was working properly previously.
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Old 12-09-2015, 11:15   #7
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Re: Perkins 4-108 Intermittent Raw Water Flow

I would second the idea of checking to see if there is ply separation in your raw water line from your engine water seacock to your strainer.
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Old 12-09-2015, 11:33   #8
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Re: Perkins 4-108 Intermittent Raw Water Flow

Whatever the cause it certainly sounds like an air lock in the raw water pump. You could try shutting the seacock off when you shut off the motor. If you do this I would recommend that you hang your key on the seacock handle so you don't start the motor without opening the seacock.
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Old 12-09-2015, 12:39   #9
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Re: Perkins 4-108 Intermittent Raw Water Flow

As I remember the pump is driven by a slot at the inner end of the shaft. Have you used a gasket that is too thick causing the pump to not engage or do so intermittently? I always made my gaskets from kraft (brown) paper bag material. Take a look at the inner end of the shaft for signs of wear.
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Old 12-09-2015, 13:30   #10
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Re: Perkins 4-108 Intermittent Raw Water Flow

I had a similar problem with my Westerbeke 104 which is essentially the same engine. Finally traced the problem to the oil cooler and engine heat exchanger. Flushed and rodded them both and the normal flow returned.
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Old 12-09-2015, 17:30   #11
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Re: Perkins 4-108 Intermittent Raw Water Flow

Quote:
Originally Posted by donradcliffe View Post
It could be that the inside of the pump is too worn to prime--if the cover plate has significant wear, turn it over.
with the symptoms you describe a worn cover plate would be the most likely cause and the simplest fix. altho really you should lap the inside face smooth with a block and course leading to fine sand paper., making sure to keep even pressure and a figure eight pattern whilst lapping, to keep the surface flat. you'll still have to do that if you use the outer face, but not as much depending on the depth of the grooves on the inner side.

Keeping hoses in good shape is smart but in your situation it's not likely the problem, as it would not be intermittent.

a quick fix if you needed the engine in a hurry would be slap some grease in the pump and replace the cover. It'll pump till you are able to stop and fix the cover.
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Old 12-09-2015, 21:04   #12
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Re: Perkins 4-108 Intermittent Raw Water Flow

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Originally Posted by tinkrman69 View Post
with the symptoms you describe a worn cover plate would be the most likely cause and the simplest fix. altho really you should lap the inside face smooth with a block and course leading to fine sand paper., making sure to keep even pressure and a figure eight pattern whilst lapping, to keep the surface flat. you'll still have to do that if you use the outer face, but not as much depending on the depth of the grooves on the inner side.

Keeping hoses in good shape is smart but in your situation it's not likely the problem, as it would not be intermittent.

a quick fix if you needed the engine in a hurry would be slap some grease in the pump and replace the cover. It'll pump till you are able to stop and fix the cover.
Agreed!

Have had the exact symptoms in the past and it was due to a worn cover plate. On our Johnson pump it was simple to take off the cover, sand off any bumps on what was the outside and replace "inside out'. If you can't source a proper gasket making one from thin paper (I've used the cover from a glossy magazine successfully) is pretty easy.

Give it a try... no cost, and if it doesn't cure the problem, it is unlikely to make it worse!

Jim
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Old 13-09-2015, 19:29   #13
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Re: Perkins 4-108 Intermittent Raw Water Flow

Had the same problem on my yanmar 3gm30f. Worn belt and pump pulley.
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Old 14-09-2015, 18:40   #14
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Re: Perkins 4-108 Intermittent Raw Water Flow

I've had the same problem, changed impeller and gasket only to realise I had a loose belt. Try tightening your belt, if you haven't already tried that.

Sent from my XP7700 using Cruisers Sailing Forum mobile app
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Old 14-09-2015, 19:18   #15
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Re: Perkins 4-108 Intermittent Raw Water Flow

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I've had the same problem, changed impeller and gasket only to realise I had a loose belt. Try tightening your belt, if you haven't already tried that.

Sent from my XP7700 using Cruisers Sailing Forum mobile app
You had a different problem. A Perkins has a gear driven pump.
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