Changed impeller, still no water

[the beave]

I changed the impeller on my '65 Merc 3.9 as the old one was shot big time but after taking it out in the water today it still was not spitting any water out of the exhaust hole. It is together right with the water tubes together. I checked and water goes thru the hole on the bottom, past the impeller and out so I know that it is'nt blocked. Is ther any way to tell if there is a blockage in the upper part of the line?

 

[emckelvy]

Re: Changed impeller, still no water

Yes; pull the lower unit off, and blow air up the copper water supply tube. If it seems to blow freely, next try hooking up a water supply to the tube. You should get a pretty good flow down the center of the exhaust tower (mid-section) if water is flowing properly thru the powerhead. If you have good flow thru the motor there's either something going on with the pump assy or you may have missed getting the water tube into the pump assy, on the "way up".

Typical places of restriction on these:

1) Chunks of impeller in the tube or upper end;
2) Upper water tube rubber grommet squeezed shut;
3) Plastic upper grommet washer melted shut;
4) Silt/crud buildup in the block behind the water jacket cover;
5) Exhaust manifold plugged up or exhaust plate perforated with exhaust blowing back into the cooling system.
6) Drain passages in the bottom of the block, or in the exhaust adapter plate underneath, plugged up.

If you're completely plugged up, I'd most suspect #2 or #3. Unfortunately you have to pull the powerhead to check. Although the powerhead's not hard to pull, especially if it's a fresh water motor.

#4 is the easiest to check for, just pull the (4) bolts holding the cyl block water jacket cover (the one over the end of the block where the spark plugs are). Use caution if the bolts are stuck, they're easy to break. To loosen reluctant bolts, apply heat (from a propane or MAPP torch).

Once you have the back cover off, you can check for silt buildup. I've seen the entire lower half (or more!) of the block plugged up inside, when that happens water won't circulate very well thru!

With the cover off, it's also a good time to apply water and see if you get anything up into the block. If not, time to start tearing more stuff apart until you find the source of blockage.

I was working on a '77 4.5 HP and it sprayed water out the telltale like no 1-cyl I'd ever seen. Turns out the discharge holes under the powerhead were all plugged up and the tell tale was the only place water could get out of the motor. Needless to say, not good for much speed above idle! Once I found this by pulling the powerhead, it was easy enough to unplug the holes and blow everything out.

HTH & G'luck.............ed

P.S. the above also applies to the smaller Merc Twins (9.8, 7.5, 6HP) as they have similar water flow characteristics.

 

[the beave]

Re: Changed impeller, still no water

OK so I pulled the lower unit again and blew air up the pipe but was only getting a small amount of air out of the exhaust hole but there was some flow. I then fought with and was able to remove the screw on the bottom of the main housing marked "fresh water flush" and found it to be blocked with a white hard substance that as I poked at it, it turned powderish. I then removed a screw type plug right above the sparkplug and there are signs of the same type of stuff in there but not as bad! Would this indicate silt/crud bulid up behind the water jacket cover? I don't really want to pull it off if it can be avoided! If I run the hose somehow into the fresh water flush hole would this be enough to clean it out?

 

[CharlieB]

Re: Changed impeller, still no water

Depends on what that 'white stuff' is made of,

I had a 9.9 on the water that kept overheating, when I pulled the stat out and started it to re-check water flow I found white chunks of grainy (sand?) flushing out of the block, kept running it (no stat or cover) until it cleared.

Crazy thing, this stuff felt grainy to the touch, but once wetted it desolved(?)

Chunks floated, broke up into individual grains and melted, disappeared. Motor ran cool, put the stat back in and call it a day!

 

[emckelvy]

Re: Changed impeller, still no water

Airflow thru the powerhead should be unimpeded. If you're only getting a little, there's no way an adequate amount of water will flow thru. You could try hooking up water to the supply tube and flushing out the hole above the spark plug. Water should gush out of there pretty good. If it doesn't, you've definitely got circulation problems. If you get good flow at that point, try plugging off the hole and see if the water flows well thru the motor, or if it just stops. That'll tell you if the "goes-outa" is stopped up!

On the flushing screw, it's kind of a "dead leg" passage that leads from the screw up to the powerhead. So, if it hasn't been used regularly to flush the motor (few are in my experience), the "dead leg" will fill up with debris. The white stuff you're seeing is from salt (or alkali depending on where it's been run) deposits/corrosion products.

So, stuff plugging up the flush port is not necessarily an indicator of what's going on with the rest of the system.

The least-intrusive thing to do is to pull the cyl block water jacket cover and have a peek inside. The gasket is common and should be available at any Merc dlr. Or get some gasket paper from an auto parts store and cut your own.

HTH & keep us posted..........ed

 

[the beave]

Re: Changed impeller, still no water

Ok so I flushed thru both the fresh water flush screw and the screw above the spark plug and got lots of flow down thru the midsection but nothing out of the hole on on the back of the case that the exhaust comes out of! I then said the heck with it and pulled the cover off of the water jacket. It wasn't overly bad. I then put the hose on the copper pipe again and there is a slow flow of water comming up thru, but there is water. A couple of times it coughed like it was going to start gushing, but never did. Is the powerhead the actual engine? Is it hard to pull it? Is there anything special I need before deciding to do this? There is a plate under the back end of the engine, what is under that? Should my water be comming out of the hole on the back bottom of the case or does it only go out down thru the midsection like it is?
Sorry for all these questions but would like to know what I'm in for before I get into it!
Thanks again!

 

[emckelvy]

Re: Changed impeller, still no water

The water should pretty much "gush" out of the cyl block area with the cover off. BTW you won't get much water out the exhaust relief hole in the center section if the engine isn't running, as the exhaust is what pushes water out that hole due to backpressure.

The "powerhead" is indeed the upper part of the outboard, i.e., the block, pistons, crankshaft, flywheel, etc.

The plate you mentioned at the back of the powerhead just covers an exhaust relief passage which doesn't usually require any servicing.

Powerhead removal on these is pretty simple; if you look under the lower cowl, you'll see a series of nuts around each side, if I recall there's (4) per side but don't quote me on that! Once these nuts are all removed the powerhead is loose but you also need to undo the carb linkage, kill switch wires (if it has a kill switch), and disconnect fuel line. If I recall those are the only interferences to powerhead removal but you should be able to tell by looking at things carefully, if anything else is in the way.

There's one nut per side at the very front, so don't forget to remove those too. The front studs are a convenient place to pry the powerhead up to break it free from the gasket.

Once you have the powerhead off, turn it over and inspect the bottom middle, you should see a passage where water discharges out the center of the motor. Blow air thru the block passages to see if they're clear and clean out if you find them plugged-up.

Replace the water tube upper grommet; the washer that lays on top of the grommet; and the powerhead gasket. Also check the condition of the driveshaft O-ring, since you've had the lower unit off a few times.

Assembly is reverse of disassembly.

Sure sounds like you've pinpointed the problem, let us know what you find when you get the powerhead off.............ed

 

[the beave]

Re: Changed impeller, still no water

I pulled the powerhead today and sure enough the plastic gromet was melted shut! Everything else seemed fine with good flow thru the motor. Went and got a new gromet, powerhead gasket and water jacket cover gasket and all is now back together. Now I just have to wait for the wind to die down so I can take it and give her a try. Will let you alll know how things work out as soon as I can. Thanks again for all the help!

 

[the beave]

Re: Changed impeller, still no water

Had it out this evening for a test run and it worked great! It had a good flow out the exhaust hole and seemed to run fine! Ran strong and kept cool. Will give it a good run on Sunday if the weather is good!

 

[emckelvy]

Way Cool Now !!!!

Way Cool Now !!!!

Sweet ! You're a Bona-fide Merc Outboard mechanic now, time to open up your specialty shop for small old Merc cooling system problems!!!!!

Happy Boating.........ed

 

[the beave]

Re: Changed impeller, still no water

Finally got out today for a good run. Was out for an hour and a half and everything was great! Too bad it didn't have more speed but it sure beats rowing...lol! Thanks again and happy boating!