Honda BF75L cooling water issues

[Cpotts]

YES, or you'll hear air coming out those two small holes at the back of the housing

removed the inlet manifold and water hoses again....
1) air flows easily from pump y junction to thermostat housing. tells me water can get through the block and to the thermostat. thermostat is missing but the housing is oddly dry even though the passage seems clear

2) the water jacket around the heads seems clear as air can pass from small hole to small hole easily
3) I blocked the lower small hole as you suggested. when I sent air through other hole (thermostat output I believe) NO AIR CAME OUT of the holes at the back of the housing or the exhaust. The main cooling flow around the heads doesn't seem to be happening.

4) I did feels some air coming out.of the thermostat input hole when conducting the test above.

the dry thermostat passage perplexed me. maybe the pressurized air is getting through but not there's not enough water pressure for water to move through the block? tell tale seems to indicate there's enough pressure. plus the impeller only has 10 hours on it.

 

[MattFL]

Have you run it in a bucket in the past without problems?

 

[Cpotts]

Have you run it in a bucket in the past without problems?

yes

 

[km1125]

3) I blocked the lower small hole as you suggested. when I sent air through other hole (thermostat output I believe) NO AIR CAME OUT of the holes at the back of the housing or the exhaust. The main cooling flow around the heads doesn't seem to be happening.

That's your problem. The passages in the head are blocked. This causes an air pocket in most of the block and the head and explains why the thermostat cavity is dry. No water can flow to it because you can't purge that air out because that air would have to go through the head cooling passages to escape before water can start flowing through that same area.

Here's one thing you can do as an additional test. Remove the spark plugs and pull the starter handle several times while the lower unit is sitting in water. This will manually run the water pump and start water flowing through the system (but slowly). You will eventually see water coming out where the thermostat sits showing that path is working fine.

If it's possible to lay the engine down so that the thermostat hole are pointing UP then you could pour some rydlyme (or any strong descaler) into the "littler" hole (not the "tiny" hole) so that it sits inside the water passages in the head. You might be able to dissolve enough to start getting some flow in there. Most four strokes you can only lay down certain ways or you cause other issues. If you can't lay it down then you could also put a tight-fitting hose in that "littler" hole and maybe use a funnel to feed the descaling solution in the hole.

 

[MattFL]

It's odd that a fresh water motor would clog up with mineral deposits, maybe it's something else (sand, grass, etc..)? It's also really odd the previous owner removed the thermostat, that's not normal. Do you still have the guys contact info? Maybe you can ask him why he removed it.

But giving it a descaling rise is very easy and maybe worth a shot if you're trying to prevent disassembling it, though the passages in your pictures look pretty clear so I'm convinced this is your problem. For the rydlyme; dilute 50/50 with water, drop the lower unit and attach a small pump to the water tube and let it run for a while. Then change the rydlyme mix for clean water and run another 10-15 min to be sure the rydlyme is all gone. Here's how I did it:

Descaling flush, motor that stops peeing

This is to share the results of a little experiment. Backstory; my 99' Honda 50 has lots of hours and gets year round use in salt. It has built up enough crumbs of sediment that the pee tube frequently gets clogged and the stream slows to a dribble or stops. The rest of the motor is flowing...

forums.iboats.com

Long story short; if the blockage is from mineral deposits , acid will dissolve it, but acids can be rough on the metal too. Especially anodes inside the motor. Products like Rydlyme claim to be safer for metals while still dissolving the minerals. There are others (Barnacle Buster, etc..), Rydlyme just happens to be the one I used with success.

 

[Cpotts]

is there a way to manually clear the water passage that outlets to the exhaust? I believe that to be the location of the blockage

 

[km1125]

It's odd that a fresh water motor would clog up with mineral deposits,

While very true, we also don't know how long this engine might have been running very hot. Could have for years and each year is a layer of deposits. The hotter it gets the more deposits you get to form - almost like a self-fulfilling prophecy. Think about how often you have to descale a coffeepot and that just goes though VERY small amounts of water each day!

 

[km1125]

is there a way to manually clear the water passage that outlets to the exhaust? I believe that to be the location of the blockage

Not sure there's an easy way unless you take the powerhead off or even the head off. You can try probing the water jacket with a small stiff wire like a thin coathanger or something similar might help.

 

[MattFL]

Stiff weed whacker string is stiff enough to dislodge some debris, but flexible enough to bend around corners and soft enough to hopefully not scrape up the metal. If it's a fresh water motor that is in otherwise great shape, at some point it might become worth it to remove the head and manually inspect/clean the passages. Especially since we don't know why the previous owner removed the thermostat, that still sits odd with me.

 

[Cpotts]

Update
I did all the same tests Inside before, but this time with water. same results

I'm convinced now the water jacket blockage is from the head to the exhaust.

And you're probably right....it's airlocked so no water can pass effectively around the heads or the block.
I'm gonna try descaler...then remove the head of that doesn't work

 

[km1125]

Good luck! Hoping you get it all fixed up!

Another thing you can add to the "mix" in trying to resolve it is using a good wet/dry shop vac and adapting the hose to that "littler" hole near the thermostat to pull on anything inside that might be plugging the passages. You might do that after you've soaked some descaler in there.

 

[Cpotts]

ok thanks for that idea. I also tried some weed wacker line but I could only insert it a few inches. the corners seem tight

 

[MattFL]

Sometimes if you spin the weed whacker string while you insert it, you can get it to walk around the corner then you can push it in further.

 

[Cpotts]

ran some descaler through the appropriate waterways....into the thermostat output and as expected it came out the tiny hole at the bottom

but then something peculiar happened

I put a plug in the tiny hole in order to keep the solution in the waterway. my though was, the descaler would work on that pesky main pathway to the exhaust.

I removed the plug 1 hour later and nothing flowed out. could that mean the exhaust pathway opened up?

put some more solution in and I watched it flow out the tiny hole AND out the hole I'm pointing at in the picture. did it several times to make sure . Is that an access point to the exhaust water pathway?

I snaked all 3 holes as best I could with Wacker line. but I had to go to basketball practice....

 

[MattFL]

I'm not sure the answer to your question, but two things: first if you're using a descaler that actually works, you're going to want to do some serious flushing with fresh water as soon as the descaling is done. From my experience, the measurement would be in minutes, less than an hour. Strong descalers can be harsh on metal. Second, I really doubt that dripping a little in the hole is going to do anything. To be effective I believe you're going to need to use a pump connected to the water pickup (remove the lower unit) and let it circulate for a while. The link I posted above shows how I did it just to give you some ideas.

 

[km1125]

I'd say that's VERY encouraging news!! They may have needed to cast that hole to make the water jacket around the exhaust. It's blocked off when you put the intake cover on, so it doesn't go anywhere. I'd do a couple more applications of the descaler and maybe even block both the small holes. You might also blow some compressed air back and forth between those two little holes and the littler hole up top. And I do agree with Matt to do some rinsing when you're done. At some point you'll just be able to run it in the tank and cycle water all the way through the system.

And when you do run it, don't run it until it stops. Do you have an IR thermometer? If so, use that on the head and shut the engine off if it gets over 160. If not, shut down when you can't put your hand on the head because it's too hot.

 

[Cpotts]

reassembled the engine and fired it up...
the idle is a bit messed up (I'm guessing from all the disassembly) but she started 2nd pull.

strong telltale

kept hand on the head to guage temperature. the engine ran for maybe a minute longer then quit. Due to the heat, I had to remove my hand before it quit.

after quitting, there was a continuous sizzling sound seemingly from the exhaust? I'm guessing I've opened the pathway, but not enough for the flow to cool the heads adequately.
would I be correct to assume the sizzling noise is the weak flow to the exhaust?

thanks Km1125 and MatrFl for continuing.to chime in

 

[Cpotts]

1

 

[MattFL]

Sizzling sound is probably water boiling or steaming off somewhere. Getting it that hot risks creating new problems.

 

[km1125]

Yep... it's probably little squirts of water hitting hot spots in the head or the exhaust that's making those noises.