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Old 10-11-2017, 14:42   #1
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Perkins 4.108 Raw Water Flow Problem

My Perkins 4.108 engine runs flawlessly, and always has. Always runs at normal temperature and excellent oil pressure. So... here's the problem I ran into today when trying to winterize the engine. I started the engine to get it to operating temperature. Checked for proper raw water flow out the exhaust, as I always do. All was fine. After about 10 minutes, the engine got to operating temp. Checked again for water flow out exhaust, just to be sure. All was good. I have a cut-off valve on the raw water intake hose just for the purpose of winterizing the engine. I made sure the raw water intake seacock was open, as normal. I had the cut-off valve valve closed, as normal, while warming the engine. I had connected a separate hose to the valve, and the hose was submerged in a large bucket of pink antifreeze, so that when I closed off the raw water valve seacock and opened the cutoff valve, the engine would draw from the bucket, instead of the sea water. With the engine running, there was maybe a 2 to 3 second delay between shutting off the raw water seacock and opening the cutoff valve to allow the pink Antifreeze to be sucked into the engine instead of the raw ocean water. However, I saw that the pink Antifreeze level was not going down, which meant it was not getting into the engine. I checked the exhaust and there was no water coming out. I blipped the throttle a couple of times, but still no water out the exhaust. I then checked the raw water impeller and it was okay. Because there were a couple of cracked vanes on the impeller, I installed a new impeller while I was in there, just to be safe. I started the engine and still was not getting any raw water flow out the exhaust, so I shut it down to think things over.

Question: Could there be an air bubble in the raw water system that is stopping the raw water from getting out the exhaust? What else could have happened? I'm stumped. HELP!
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Old 10-11-2017, 16:23   #2
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Re: Perkins 4.108 Raw Water Flow Problem

Connect direct to the pump and see if it make a difference. Also try and prime the pump as you don’t have the pressure associated with sitting in the ocean.
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Old 11-11-2017, 05:51   #3
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Re: Perkins 4.108 Raw Water Flow Problem

When I test my 4-108 on the hard, I almost always have to give the pump a little push. (Hose to the pump inlet hose.) You would think they will self prime, but not so all the time. RBK is correct.

I had thought to put a Y valve on the inlet to serve as an emergency bilge pump, but the priming bit has me stumped due to access and lift from the sump.
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Old 12-11-2017, 03:55   #4
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Re: Perkins 4.108 Raw Water Flow Problem

I lube the insides of my salt water pumps with waterproof grease when I change or inspect impellers. The grease protects the impeller before water is moving and increases the suction. Usually a finger of grease rubbed on the housing, shaft and plate. Method is in older manuals of some engines. I get about 5 years out of my impellers. 2 Detroits, 4108 and Onan.
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Old 12-11-2017, 12:05   #5
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Re: Perkins 4.108 Raw Water Flow Problem

Well, you guys were right. I had to remove the intake hose from the pump and attach a hose to gravity feed the pump with winter coolant (pink). It then began sucking fluid immediately when I started the engine with that hose connected. Thanks all for the input.
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Old 21-11-2017, 01:44   #6
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Re: Perkins 4.108 Raw Water Flow Problem

Never run the Perkins with raw valve shut,you will be running impeller dry.
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Old 21-11-2017, 05:20   #7
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Re: Perkins 4.108 Raw Water Flow Problem

Rubber Impeller pumps should be self priming, if they’re not the usual causes are worn cover plate, worn impeller, or worn cam. Any of these items worn can also reduce pumped volume.
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