Nissan 5hp water pump issue

[svscott]

I've got a 1999 Nissan NSF5A outboard that I'm reviving as a spare motor. The telltale isn't shooting any water. I poked a wire up the hole but it didn't help. I replaced the impeller and the old one was missing 3 of 6 tabs. 2 of the tabs were easily picked out of the circular water passage under the impeller wear plate but the 3rd tab is MIA. Maybe the tab somehow backflushed out the intake screen and into Lake Erie, or maybe it migrated upstream (more on this later).

Although there is no water from the telltale, there is exhaust blowing out the telltale. I used a ball inflating needle and a good compressor and blew air backwards through the system and air bubbled out of the water bucket. Tried starting again but still no water. I took the power unit off the outboard and removed the vertical copper supply tube from the top of the water pump then ran a wire through and blew air to ensure it's clear. I took the impeller apart, verifying the key was still in place and no torn gaskets. I put the lower unit back together and installed onto the outboard case without engine then I put my cordless drill onto the driveshaft in place of the gas engine and ran the drill to spin the prop and impeller... but still no water is coming up from the copper supply tube. I took impeller apart again and it seems like the rubber bushings for the 2 different copper tubings all seem to be pliable and sealing... but maybe not.
The only thing I can find that's visibly worn or out of whack is the thin steel retainer cup that holds the impeller is slightly ovalled where the driveshaft passes through it. Maybe it's losing a vacuum there... but it's only slightly out of shape.
I cut away the lower gasket that covers over the water passage under the impeller wear plate to make sure the passage is open and I can't go any further with the testing until I replace that gasket.

I'm not a trained mechanic by any stretch but my whole adult life I've been maintaining a small fleet of bicycles cars, trucks, vans, motorcycles, tractors, trailers, etc. and I'm losing my mind on this! What could I be missing?

The Nissan was bought new by my dad in 99 and given to me in in 2005. I have been running and maintaining it since.
It got retired and replaced by it's virtually identical Tohatsu Sailpro 6hp last year after the engine suddenly quit running. After much diagnosing and swapping parts from the new engine into the old one and vice versa (they all worked on the new Tohatsu) and after doing a valve adjustment, replacing carb, replacing fuel pump and filter, spark plug, and ignition coil, I finally replaced the exciter coil this morning and the engine is running like new again, only now with no water cooling.
I'm going to order the new water pump gaskets and retainer cup. I was hoping to find a complete rebuild kit but the parts diagram lists everything separate.

I'm stumped.

[Jimmyt]

The impeller housing should be replaced before you do anything else. This is likely your problem. Without seeing it in person, I won't bet my paycheck. But I replace both parts when changing impellers. The impeller rubs on the housing, as well as the wear at the shaft. So, there are a couple of failure modes associated with the housing...

Also, were you careful to get the impeller blades angled correctly when you replaced it?

Sounds like you're doing a good job of troubleshooting, though. Good, logical progression. You'll get it. Hang in there.

Everything above the impeller is pressurized, generally speaking.

Did you have the water level above the impeller when you were in the bucket?

[svscott]

I will probably just order all of the surrounding water pump parts and hope that fixes it.

I'm pretty sure the impeller blades freely switched direction when I hand spun the prop the opposite way. It has been several weeks since I removed the old one and I think it went back in the same way... but maybe not.

The water was about 3 inches over the inlet.

Am I correct in thinking that spinning the driveshaft with a cordless drill in place of the engine should make the impeller pump water up the shaft to the top end?

[Jimmyt]

Am I correct in thinking that spinning the driveshaft with a cordless drill in place of the engine should make the impeller pump water up the shaft to the top end?

If your drill will spin the shaft at 1100-1300 rpm (verify idle speed for your engine) AND you were spinning it in the correct direction, it should pump.

Was the pump casing submerged, or just the inlet at your 3" over the inlet level? Having water over the shaft penetration of the casing might allow it to pump - even if the casing seal was bad. Something to try while waiting for parts maybe.

If you can blow compressed air through the entire cooling path, without noting a restriction, it's probably the impeller/casing that's causing you grief.

Have you verified the intake is clear to the pump casing? Blow directly from the pump intake back through the inlet screens/ports, etc...

[Be Free]

The only thing I can find that's visibly worn or out of whack is the thin steel retainer cup that holds the impeller is slightly ovalled where the driveshaft passes through it. Maybe it's losing a vacuum there... but it's only slightly out of shape.

The area where the shaft passes through the top of the impeller housing is under pressure, not vacuum. If you don't have a good seal here your pump is just going to put the water back into the foot and out the exhaust.

I'm pretty sure the impeller blades freely switched direction when I hand spun the prop the opposite way.

You can get away with this on a new impeller. An old one will likely break off one or more fins. In any case it's not good for the impeller.

The impeller housing should be replaced before you do anything else. This is likely your problem. Without seeing it in person, I won't bet my paycheck.

+1. It really sounds like your impeller housing is seriously worn. It's not expensive and no harder than what you've already done. Change them both.

Although there is no water from the telltale, there is exhaust blowing out the telltale.

This part worries me a little. There is not supposed to be any connection between the telltale and the exhaust. It is possible that the exhaust is entering the water pump through the top of the worn impeller housing or running backwards from the foot and exiting the telltale. Either way there's no water in the water jacket. Let's hope it's something like that. The other possibility is a blown head gasket.

[Jimmyt]

The area where the shaft passes through the top of the impeller housing is under pressure, not vacuum. If you don't have a good seal here your pump is just going to put the water back into the foot and out the exhaust.

Hope we can have a friendly disagreement over this point. .

The intake portion is under a vacuum, and air leaks at the shaft will prevent the pump from pulling water into the intake. The pump is well above the intake water level when the boat is planing, and possibly at idle, depending on how the motor is mounted. Still not sure that his bucket water level submerged the pump housing past the shaft penetration.

I do agree with you for the compression portion of the cycle, but if you can't pull water into the pump chamber at the intake, there won't be any to leak out as you attempt to pressurize it.

My thinking on the exhaust through the telltale is, the entire cooling system is dry. Exhaust can backflow into the water jacket due to the lack of any water in it. Both the water discharge and exhaust are combined and exit through the foot/prop hub together. Put the prop hub under water, and you have adequate back pressure to force a small amount of exhaust back through the cooling jacket to take the path of least resistance out the telltale.

Just hope the totally new pump assembly takes care of it; and it's not that missing vane or some other foreign material wedged in an inaccessible spot. We have mud daubers here that build entire condo units in anything you leave accessible to them...

[Tomfoolery]

Both the water discharge and exhaust are combined and exit through the foot/prop hub together. Put the prop hub under water, and you have adequate back pressure to force a small amount of exhaust back through the cooling jacket to take the path of least resistance out the telltale.

I don't know about others, but the BF50 has a dry exhaust above the water line that actually does discharge exhaust gas at idle. When it's running fast enough it will come out the prop hub, and if the prop is actually driving the boat (not in neutral), there is a vacuum there that will pull exhaust out. But absent that hub vacuum and high exhaust flow, it all exits out that little oval exhaust port. So it's conceivable that with no water in the system, exhaust could also make its way through the water passages in the engine and come out that pee tube.

[Jimmyt]

Both the water discharge and exhaust are combined and exit through the foot/prop hub together. Put the prop hub under water, and you have adequate back pressure to force a small amount of exhaust back through the cooling jacket to take the path of least resistance out the telltale.

I don't know about others, but the BF50 has a dry exhaust above the water line that actually does discharge exhaust gas at idle. When it's running fast enough it will come out the prop hub, and if the prop is actually driving the boat (not in neutral), there is a vacuum there that will pull exhaust out. But absent that hub vacuum and high exhaust flow, it all exits out that little oval exhaust port. So it's conceivable that with no water in the system, exhaust could also make its way through the water passages in the engine and come out that pee tube.

Very interesting! Wonder if the tohatsu 5 has a similar port. I also wonder how much exhaust that small port can pass...

I know when I run my Etec on the hard, it cackles like straight exhaust from the ports; but is very well mannered when the foot is in the water. That leads me to thInk that most, if not all, of my exhaust is through the submerged portion. Maybe it has a muffler section for the dry exhaust?

Anyway, thanks for that information!

Seems like the consensus is, cautious optimism that exhaust at the telltale doesn't necessarily mean a blown head gasket - fingers crossed.

[Tomfoolery]

Both the water discharge and exhaust are combined and exit through the foot/prop hub together. Put the prop hub under water, and you have adequate back pressure to force a small amount of exhaust back through the cooling jacket to take the path of least resistance out the telltale.

I don't know about others, but the BF50 has a dry exhaust above the water line that actually does discharge exhaust gas at idle. When it's running fast enough it will come out the prop hub, and if the prop is actually driving the boat (not in neutral), there is a vacuum there that will pull exhaust out. But absent that hub vacuum and high exhaust flow, it all exits out that little oval exhaust port. So it's conceivable that with no water in the system, exhaust could also make its way through the water passages in the engine and come out that pee tube.

Very interesting! Wonder if the tohatsu 5 has a similar port. I also wonder how much exhaust that small port can pass...

It can't pass much, but it doesn't have to at idle. I'm sure that's why it's there, to prevent excessive back pressure at idle since it would take relatively substantial pressure to push the exhaust out under water. With the prop engaged, the vacuum at the center aids in pulling exhaust out, and I doubt much if any is coming out that little port when running at speed. You can certainly see the bubble stream coming out of the prop hub when in gear, but I've never checked to see how much, if any, exhaust is coming out the little vent port.

And in the driveway, you can certainly hear it coming out the port. No mistaking an unmuffled engine at idle.

[svscott]

For sure the water bucket was plenty high on the shaft. I've run it in the same bucket dozens of times.

I am convinced the engine's water passages are clear, and I've gone through the entire water pump and it's passages more than once, even cutting away gaskets and taking each component apart. That 3rd tab is nowhere to be found! Aside from the igniton system being fixed, I did compression test and adjusted valve clearances. I don't think there's a blown head gasket but I have not done a leakdown test (I've never done one in any engine). After working on the outboard for a week last season (then giving up due to replacing it) and now a couple days this season, the engine now starts on first pull and runs nice but without water, I only ran it a minute or two total.

It'll probably be a couple weeks before I get back into this project. The weather is improving enough to actually sail, and the parts for my Honda BF50A arrived. I've got a bunch of routine maintenance on that engine because I've got no idea of it's maintenance history so I'm going to do the water pump assembly, thermostat, spark plugs, oil/filter change, gear oil change, and replace the very rusty main pivot bolt. I'll check the timing belt and maybe do a compression test while I'm in there.

[Be Free]

Hope we can have a friendly disagreement over this point.

One of the things I like most about this forum is that most of the disagreements are friendly. I don't think we are in any significant disagreement. I was concentrating solely on the symptom of exhaust (and no water) at the telltale and what may be causing it. My assumption was that if the pump was able to draw water up from below it would exit around the shaft and back to the foot rather than making it's way to the indicator. I'm in total agreement that the intake is under vacuum and that the outlet is under pressure.

I believe we are also in agreement that the likely cause of exhaust in at the telltale is a dry water jacket allowing exhaust to move up from the foot and out the indicator hole.

I don't have any first-hand experience with the exhaust system of a small Honda but the older small OMC engines I have worked with did not have a through-hub exhaust. All of the exhaust came out under water but not through the hub. If that is true of the small Honda engines as well then there would have been less back pressure in the empty water jacket than in the exhaust port even though it would only be a few inches under water. I leave it as an exercise for the student to calculate what percentage of the exhaust (by volume) will exit each point while the engine is idling in neutral.

[Be Free]

Tom,

I don't think you have a compression problem in your 5hp engine. I just mentioned it for completeness. The dry water jacket is the most likely source for the exhaust at the telltale. I think you will be pleasantly surprised when you rebuild the water pump.

You are doing everything right on your BF50A. That's just what I would do if I had a new (to me) engine with unknown service. This way you will know when (and how) the maintenance was done and you can go forward from there.

Have you examined the tube that the engine tilts up on? If it's not been replaced it may be showing significant rust on an engine as old as yours.

Now, go sailing.

[Be Free]

Sorry Tom, it was svscott who posted. The rest of the post remains unchanged.

[Jimmyt]

I don't think we are in any significant disagreement.

... I leave it as an exercise for the student to calculate what percentage of the exhaust (by volume) will exit each point while the engine is idling in neutral.

Absolutely agree.

[svscott]

You are doing everything right on your BF50A. That's just what I would do if I had a new (to me) engine with unknown service. This way you will know when (and how) the maintenance was done and you can go forward from there.

Have you examined the tube that the engine tilts up on? If it's not been replaced it may be showing significant rust on an engine as old as yours.

Now, go sailing.

It's funny you ask about the main pivot shaft bolt for the Honda. I ordered the bolt and new washer/nuts from the dealer a week ago and picked it up today, along with a water pump assembly. I got the pivot bolt and hardware changed today and also swapped the water pump assembly, plus did engine oil/filter and gear oil, new spark plugs , checked compression on all cylinders (all exactly the same at 175 psi), and inspected the timing belt. I also have a new thermostat to install but I ran out of time this afternoon before I had to hop on the motorcycle and go help my friend lay up fiberglass to repair some keel to hull damage on a C&C 29 he just bought.

It's unseasonably warm here so I had the 26D out yesterday for this first trip of the season. This has to be the earliest I've gotten on the water. I've got a lot of irons in the fire right now with work and other projects but I'll fit sure be sailing again sooner than later.