Yanmar 3YM30 raw water cooling system problem

[Vegas]

How long should I run the engine to see if the impeller will prime and pump water, knowing that running it "dry" for too long will affect the new impeller I just installed?

Start of the issue was that my engine temp alarm went off and I noticed no water pumping with exhaust. I had to be towed in. I put in new impeller (old one looked ok, however). The impeller is turning, because I ran it for a few seconds with the impeller faceplate off, and observed it rotating. Removed the intake hose and carefully opening the thru hull indicates thru hull is clear. Hose from intake thru hull to seawater strainer is clear, as is the hose from the seawater strainer to the impeller. Seawater strainer is clean.

I took off the impeller "out" hose and ran the engine for 10-15 seconds and no impeller water output, even with the new impeller.

Am I not running engine long enough for it to "prime"? How long can you run it dry without
ruining the impeller. If impeller is turning, and plumbing to the seawater thru-hull is not clogged, what can keep the impeller from pumping water? Do I need to replace the entire water pump assembly?

 

[Davidasailor26]

To help the pump get a prime you can try to open up the strainer and pour some water in it before starting the engine.

The only problem that could prevent water flow that you haven't checked for would be an intake hose collapsing under suction, but I'd be surprised if that was happening on a boat that age.

 

[Davidasailor26]

One more thing to check - make sure that the o-ring on the strainer is seated properly and that it can't pull air. When the engine is running the strainer should have about an inch of water in it and you should see more getting sucked in.

 

[Stu Jackson]

One more thing to check - make sure that the

faceplate is smooth. You may have to sand it some. If you can see grooves, that could be your issue. Your troubleshooting work was very good. You have identified it as AT the pump, water TO pump, impeller spins, no water OUT. So...??? Good luck.

 

[Vegas]

Stu: It is pretty smooth but there is the slightest groove visible. Here's a picture but not sure how well you'll be able to ascertain the depth of the groove. Do you think that could be the problem? I can't imagine why that slight groove would make a difference, however you are the third source of that groove info today so I'm going to sand it smooth and see if it helps! Thanks!

 

[dave_and_dd]

when you re-assemble the pump, either coat the insides well with Dawn DW detergent or even KY jelly. that will help draw a suction and pull in the prime. if it is drawing well, it should prime very quickly, you don't have to run it long dry to say it isn't working...

Dave - Tampa, fl

 

[Vegas]

A friend suggested turning the cover plate inside out.....I mention that because if it works, it could be a good temporary fix out on the water. My plate has lettering stamped into the outside, so I don't know if that lettering would have the same negative effect as grooves do.

 

[Allan12210]

Check that the hose fitting into the exhaust riser (mixing elbow)isn't clogged. About every season salt crystals form in mine and completely block that little bronze fitting. If the water can't get out it won't come in. You could pull the hose off the riser and stick it in a bucket. With no backpressure the pump should prime and flow quickly.

 

[Davidasailor26]

You have identified it as AT the pump, water TO pump

Stu, my only concern is that while the lines to the pump may be clear, if there is a chance to pull air in at the strainer then that would break the prime. The strainer on the Beneteau is above the waterline so it relies on a seal to pull water through, and a bad seal would not leak water.

 

[Newport Bob]

From my experience- my strainer is above the waterline and I usually fill the 2 hoses ( to thruhull and to pump) and strainer basket with water when I first commission in the spring, screw on the cap then open thruhull and start - all OK. HOWEVER, did have your problem one year - air leak at the strainer. A little petroleum jelly on the o-ring solved the problem.

 

[kloudie1]

Strange.. That faceplate does not look to be touching the sides of the impeller blades/vanes..?? Usually the inside of a properly fitted plate will be shiny across except for the middle. Methinks the gasket is too thick or there are two in place? The impeller blades/vanes must touch both sides and the tips should be in contact with the case all the way around.. bent a lot more on the cam, but bent back a little opposite the cam.. If the impeller sides or tips don't contact the case, it will not pump nor will it even try to prime.
Could be a wrong impeller too.. If the impeller is ten thousandths of an inch too narrow, it won't work. one quick way to check is to push the impeller all the way in the case then put a good straight edge across the case face.. If that straight edge does not touch the impeller, the impeller is too narrow.

 

[Jim 5757]

Looks like you have the "beloved" Sherwood pump. According to your posts, by removing the pump output hose you have eliminated any issues with everything downstream of the pump, so don't worry about that stuff. I agree with Newport Bob that you could have an air leak at the strainer, but you could test that by running a line direct from intake to pump. To refresh the cover plate may I suggest you place a sheet of wet-or-dry sandpaper on a sheet of plate glass and sand down the inside face of the pump cover. Working in a sink with water running will lubricate, flush and yield a nice finish. I used 400 grit. Sand in a circular or figure-8 motion until the surface is smooth and free of ridges.
Please let us know how you make out!

 

[Vegas]

It's pumping water now!

Not sure which change did the trick:
1. turned the impeller face plate around, with copious amounts of vaseline on the o-ring;
2. turned the o-ring in the cap of the seawater strainer around...noticed it was flattened somewhat on one side...so by turning it around a more rounded, "new" surface would create the seal. Also put more petroleum jelly on that seal, and tightened it a little tighter than my previous practice;
3. primed it by filling both hoses to the impeller with soapy water, with the thru-hull closed, then started the engine and opened the thru hull a few seconds afterward.

Thanks to all your input!!!

Unfortunately I discovered a small leak from the area between the rear of the water pump and the engine. Haven't totally tracked it down yet but suspect it is a leak from the pump shaft between the impeller and the pulley. Have around 1400 hours on the engine and believe it is the original water pump...........so..........will be tackling that next!
.

 

[Jim 5757]

Oh yeah baby! The seals are shot! That pump has a carbon bushing and two seals... one to keep the water out of the engine and one to keep the oil in. I messed with ours for 5 years rebuilt it twice before giving up and buying the Oberdorfer.

!

 

[Scott B]

It was most likely the vaseline that did it? The 3YM30 has the Johnson pump. The groove in the face plate is for the O-ring which is in the face of the pump and should be changed when you change the impeller. The impellers used to come with a small packet of lubrication, but no longer. I would trun your face plate back around and install a new O-ring.

FYI, the AWAB flexible nut driver works great for the nuts on the face plate.