Raw Water Problem

[JWSutcliffe]

We are having an intermittent raw water problem with the Universal M25 in Oryx. When I start the engine the first time of the day I have plenty of water running through the muffler and out the exhaust. After sailing all day we start the engine and have no raw water flow. Running up to max rpms will not start the water flow, and the engine overheats. I have verified that the inline strainer is clear and that I have water flow up to the raw water pump inlet. I also have a brand new impeller in the pump. If we disconnect the hose from the heat exchanger to the muffler and blow through it there is no blockage in the muffler and beyond. If I start the engine this way the water flows from the heat exchanger, and will then flow through the exhaust once we reconnect the hose to the muffler. I am baffled - any ideas?

[mattlydon]

I have a similar problem - if the engine intake comes out of the water, it's likely that the raw water pump looses prime.

I find if I start the engine at LOW idle, the pump seems to prime wihin about 30 seconds - it's nail biting time until the water comes out.

If I remember to close the seacock before sailing, I seem to be able to retain prime, and have no issues. Of course, you need to remember to turn it back ON before starting the engine again.

Matt

[Mitch F]

Did you lube the impeller? Smear some vaseline on it and you might find the problem solved. We have to do this to the pump on our MD7A sometimes.

[Steve Laume]

If pump tune up might help you could also check the condition of your cover. On my old pump the cover had a groove scored into it by the impeller. I took this home and ran it on a belt sander to progressively finer gits until it was flat and polished again.

I doubt seriously that this is your problem but but it couldn't hurt to help with maximum performance of your water pump.

Problem solving is much easier when something just plain breaks, Steve.

[sharkbait]

A positive displacement pump should draw water almost instantly.

Your rubber impeller pump is a positive displacement pump. It should be self priming. I suspect that you are some how drawing air. The above comment about inspecting the cover plate of the pump is valid. You should also look at everything between the pump and the thru-hull. Somewhere there is an air leak. Look closely at the seals on the strainer. And, check the gasket on the pump cover plate.

[Jim Walsh]

I believe you have an air leak. I replaced my M25 with a M25XPB but I retained the original seawater strainer and the raw water hose from the seacock to the strainer since it was in fine shape and of recent vintage. I have never lost prime. I always ensure a healthy flow of water through the exhaust as a matter of routine.

[Phil Shedd]

I would also say you have a air leak on the suction side of the pump. Make sure the grease cap is full of grease and screw it down so you know there is lots of grease in the seal area. Air can get in that way if there is little or no grease.

I have a m25 in my cd31. The basic set up with a strainer before the pump .There is always a good flow of discharge water. Also check the gasket for the strainer

Went for first sail of the season yesterday was Great.

Phil

[Bruce Barber]

Another possibility is pressure loss within the pump. I know nothing about your pump, but the impeller in the pump on my Yanmar 1GM had worn the cover and cam enough that it would no longer pull water from a bucket below the level of the pump (I flush the engine with fresh water at shutdown.) Replacing those two parts made a big difference. Not the same situation as yours, but it goes to show that internal wear can sometimes be significant.

[cbrenton]

I changed my impeller last week-end and put the raw water hose in a bucket. Started the engine and no water in the exhaust. I noticed that two screws on the cover plate were not completely seated. I was able to remove some debris from the bottom of the screw holes with an awl, then screwed a tap into the holes. Replaced the cover plate and it worked fine.

[Dean Abramson]

Skip, I also think this is an air leak. Maybe somehow, when the engine is hot, the leak is worse.

If you do not have a SpeedSeal cover for your pump already, maybe this is a good time to try one out. Perhaps you would get a better seal; they come with a rubber O-ring. (But the main reason to buy a SpeedSeal is the simple hassle-free access to your pump innards.)

Good luck.

Dean

[Maine Sail]

One thing not yet mentioned is the possibility of a collapsing hose wall under suction. This happens often with older wire reinforced hose where the inner membrane detaches from the outer wall and under suction it collapses and prevents flow. This will only happen on the suction side not on the pressure side.

[Dean Abramson]

Maine Sail makes a good point. I could see where a soft hose might get softer when it's hot.

[JWSutcliffe]

I pulled the whole raw water system apart today. I found four possible contributors to the problem:

1. Some residual old gasket material on the pump cover face and pump body. I cleaned that up.

2. The replacement gasket I used was fairly thick. I Made a new gasket from thin paper and installed it instead.

3. The hose at the junction with the exhaust elbow was partially blocked. I replaced all hoses.

4. The check valve on the anti-siphon elbow was old and sticky. I replaced it.

I ran the engine several times and got good water flow each time. Didnt have a chance to go out sailing and prove the results, but I will by this weekend. I am also going to order a new raw water pump, as the existing one looks like the seals are probably about worn out.

Thanks for the input, guys.

[sharkbait]

You can order a new pump but you should also order a seal kit for the old one. Rebuild the old one and keep it as a spare.

[Dean Abramson]

Skip, please report back on the results.
Thanks,
Dean