Baffled by Raw Water Cooling Problem

[Greg Shakeshaft]

The brass union that connects to the inlet side of my Johnson F4B-9 Impeller pump broke off the other week and consequently needed replacing. I took the opportunity to take a closer inspection of the impeller whilst my engine was out of action and I'm glad I did as some of the blades were beginning to crumble. I ordered a service kit and whilst waiting for it to arrive, I took the pump off and stripped it down to check the bearings etc. Once the kit arrived it was a simple and straight-forward job of swapping old with new and soon the pump was re-assembled and back on my engine.

However, despite repeated efforts to 'prime' the system it just would not draw water up from under the hull into the strainer box. I was taking the boat out of the water anyway for it's annual clean and antifoul and thought that maybe some marine growth had managed to suck itself up and cause some blockage around the inlet under the hull. Once the boat was on the hardstand I was able to attach a hosepipe to the seacock inside the engine and give the entire inlet a good flush in the hope that if anything was in there, it would be dislodged. Water poured out easily and thus convinced me that there was nothing blocking the inlet under the hull. I was not able to do any more testing until the boat was back in the water.

The boat went back in yeaterday and although I had primed the raw water system prior to her being lowered into the marina unfortunately, when I started the engine and motored back to my pen, very little water was coming from the exhaust. Fortunately,i only had a about 100 metres or so and thus it was never going to be a real risk however, on arriving back I immediately started to strip down the entire raw water system in the hope of identifying the problem.

I took the pipe leading from the seacock up the strainer off and flushed that out with a water jet. I then removed the pipe from the strainer to the impeller and did the same with that. With the stainers pipework removed I took the opportunity to unbolt the strainer and gave that a good wash in a bucket of fresh water and checked the strainer was serviceable and the seal around the lid was secure and working correctly. I then refitted the strainer and all the associated pipework. Then I removed the impeller cover and made sure that the impeller was indeed going round on the shaft and it was correctly installed. Everything appears to be just fine. I then moved to the section on the outlet side of the impeller. This is just a short piece of hose that bends round and attaches to the heat exchanger union. I double checked that there was no blockage in this area.

At each seperate point of this process I started the engine to see if I had resolved the problem but to no avail. I even attached a length of clear hose to the outlet side of the water pump hoping that even if the raw water would not pass through the heat exchanger, I would at least see it exiting the pump. But it wasn't even making it that far.

Why won't the pump do its job? It has all these new parts in it, it should work better than ever but for some reason, it just won't work. Am I priming it incorrectly? I close the seacock, unscrew the top of the strainer box and pour water in. The water travels down the pipe back to the seacock easily enough and it also travels down the pipe that leads to the pump. I ensure that strainer is full of water before screwing the lid back on. I open seacock just seconds before starting the engine, the initial water that was sitting in the strainer gets sucked through the system and is forced out of the exhaust as it should but no new water is pulled up from under the hull. Something strange is happening and I am at a loss as to why I cannot get it to work.

Any ideas would be gratefully received.

[Sailmonkey]

Did you put in one of the seals backward allowing the pump to pull air more readily than water?

[Tim R.]

The cover on the pump could be worn. Check it for scoring. Even a tiny bit of wear will significantly reduce the ability to pump water. It is not much more money to install a Speed Seal rather than replacing the cover with the factory part.

It could also be that your are sucking air somewhere. because all you did was replace the inlet, I would make sure it is installed properly.

As for priming, I would backfill as you stated but not open the seacock until the engine has run about 5 seconds.

[Greg Shakeshaft]

Thankyou Sailmonkey & Tim for your suggestions and recommendations.

Firstly to Sailmonkey.... Which seals are you referring to? I have pulled so much apart over the past couple of weeks, I'm not sure whereabouts in the system you are referring to.

Secondly to Tim... When I purchased an impeller kit, it came with a new gasket for the cover. I lightly sanded the existing faces with very fine wet n' dry to emove any imperfections and remains of the old gasket. the two faces appear to mate well and all of the 6 screws holding the cover in place have been replaced with new ones as theses were also included in the service kit, The inlet and outlet unions were replaced at the same time even though it was only the inlet union that actually broke (corroded away) as I guessed that it would not be too long before the outlet one did likewise. I will try your suggestion of not opening the seacock until 'after' the engine has started and see if that helps.

Cheers, Greg

[Tim R.]

Greg, the surface of the cover I am talking about is where the impellor rides. Try removing the gasket and using a very thin bit of RTV sealant. This effectively closes the gap between the impellor side and the cover. If this helps, I would replace the cover or get it machined flat again.

[Sailmonkey]

I was referring to the lip seals in the pump.....did you remove those when you stripped it down to inspect the bearings?

[Cheechako]

just curious.... doesnt your sea strainer fill with water on it's own when the boat is in the water? Were pieces of the impellor mising when you took it out? there could be pieces jammed in the heat exchanger.

[Greg Shakeshaft]

Thanks again to all of you for assisting in my dillemna...

Tim... I will certainly consider replacing the gasket with RTV sealant however, prior to the union snapping, the impeller was running perfectly. However, thanks for the suggestion, I will keep it in mind.

Sailmonkey... Yes the two lip seals that sit on the shaft either side of the bearings were removed when i stripped it down. I took careful note of which way round they were facing as the service kit included two new ones which I inserted. They went in without a hitch and appeared to be correctly seated. Thanks once again for your thoughts.

Cheechako... My sea strainer sits approximately 16-18" above the seacock roughly at the same height as the cylinder head/heat exchanger casings. Water entering the plastic pipe that joins the seacock to the strainer never rises more than about 8" up it which I am guessing is the waterline. The only way to fill the strainer and the hose leading from it to the inlet side of the impeller is by closing the seacock and pouring into the top of the strainer before replacing the screw cap. Regarding the possibility of bits of impeller blocking the heat exchanger. When I removed the rubber hose from the outlet side of the impeller, I placed the end over my mouth and blew hard. There was absolutely no resistance and a bubbling noise (water in the exhaust pipe system) could easily be heard. later, when I was struggling for ideas as I had done everything possible to sort the problem out, I did remove the heat exchange cover and inspected the veins for any types of blockage. Whilst, I do feel that they would benefit from a proper clean they nevertheless look in reasonable condition. I know that to remove them will require the disassembly of the fuel filter and fuel lines and for the moment I feel that I already have enough problems without creating additional issues to have to work through. One problem at a time is more than enough

Cheers again everyone. Anymore suggestions, ideas, etc. will be gratefully received.

[um saudade]

I often have a hard time visualizing the exact layout of things when people try to describe things but this seems pretty straight forward. If, as I assume, both the inlet and outlet sides of the pump are connected with hose-- Did you reverse the hoses???

I have seen before where everything was done right and owner was sure the hoses went "there" but they were reversed. It takes a nearly catastrophic failure before this system will not pump at all and should prime itself easily.

Good luck

[Therapy]

What are the chances that the kit had the wrong impeller in it?

[Nor'Sea 27]

Disconnect the seawater to mixing elbow hose with the motor idling. This will verify that the mixing elbow water passage is not full of debris and thus blocking the outflow of seawater.

Check the elbow fitting where the waste seawater hose connects to the mixing elbow also. These elbows frequently are made of steel and will have rusted inside thus preventing seawater flowing out into the mixing elbow and overboard.

Oh yes-- also check the suction side hoses that might crimp when the pump is turning but will appear normal when the motor is off.

Charles

[sailorchic34]

Ah, In order to pump water, the impeller must be tight against the forward wall of the pump with just a slight compression of the rubber at the aft plate. I found out that it is possible to fit the impeller, so there is a small gap at the front of the housing. This keeps the impeller from forming a seal.

A good test is to blow through the inlet port, if the air moves easily, the impeller is not seated all the way. If its hard to blow air through it then its fitted correctly.

Don't ask me how I know...

[Greg Shakeshaft]

Thankyou all once again. Your suggestions have been invaluable. Might I reply in order as follows...

Um Saudade, Yes, the reverse issue was one of the very first things that crossed my mind. I had taken a photo of the layout with my camera/phone prior to dismantling and double-checked with this as soon as the problem came to light. Every connection is exactly as it should be.

Therapy, hmm, you know, I did start to wonder if I may have been sold the wrong parts. The kit came in a box but it wasn't sealed. I actually removed the impeller again yesterday and photographed the markings on it to ensure it was indeed the correct one for my pump. It says 'Johnson 810 B-1' on it so I'm satisfied that it is the correct one for my setup.

Chas Erwin, I do like this suggestion very much and will investigate further today. Up to now, I have been concentrating all my efforts on the inlet side of the Heat Exchanger from where water is drawn into the boat on the bottom of the hull, up past the pump and onwards into the engine casing. At no time have I looked at the other side and whilst I have put my mouth around the hose that attaches to the inlet side of the heat exchanger and blown and the airway appears clear, I am not 100% aware of where the air is travelling when it leaves the other end. I have a couple of "T" junctions at that end, one leading to the prop seal for lubrication and another linking up with the exhaust system. It's all a bit complicated to explain and I'm no expert but I will have a closer look in this area.

Sailorchic34, Yes, I did wonder if the impeller blades were fitting snug against both the the inner wall of the pump and the cover plate. I have attempted to blow into the inlet union but like you said, no air will pass through so I am confident the seals are good. Thanks for your suggestion though.

Well, I really do appreciate everyones help with this. I will certainly look forward to updating you all after I have investigated Chas Erwin's suggestion.

Cheers.

[s/v Jedi]

Did you make sure the impeller is turning? With the seacock closed and pump open, while pushing the stop button (so that engine won't start), hit the starter for a second and see if it spins.
The impeller hub might not be secured to shaft or rubber part of the impeller.

Also, the pump housing has an internal cam which bends the impeller blades all back as they pass. This cam wears out and needs to be replaced when that time comes.

The pump housing lid can be sanded with wet paper and an orbital sander in very short time. These ridges must also go. Check for any wear or damage inside the pump housing too.

Last test: remove input- and output-hoses from pump and put a yard of different hose on the input with it's other end in a bucket. Put another different piece of hose on the pump output and back into the bucket. Now verify if it pumps.

You can only run the engine for seconds as the exhaust doesn't get the raw water injection. When you have plastic components in the exhaust (like a Vetus waterlift etc.) then seconds is a lot already.

Good luck!

[Gabrieln]

I'm sorry for asking such a naive question. But are you sure the impeller is locked to the shaft?