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Honda BF90AW Doesn’t Pee With Flush

L

Lunasea

Member
Ok…I’m stumped. I now have a 1998 BF90AW that is a freshwater beauty. Bought it to replace my 1999 BF90A that developed water in oil (had been in salt water all its life).
Here’s the issue….the new motor pees well when running and intake well submerged at launch. However, it will not pee any water at all when a garden hose with great pressure is attached to flushing port. I do note water coming from exhaust while flushing…..just not a drop through telltale.
So…how can I believe that flushing with a hose will actually flush the entire motor? Obviously this is pretty concerning having a motor that ran beautifully and was faithfully flushed still develop a water/oil communication.
I should also note that the 1999 would pee a 10’ stream when flushed!
Hopefully someone can shed some light. I did spot a video by a member here (Dave C) that seemed to be related, but was a BF90D. I believe he changed the thermostat, flushing port, and pressure relief. Sounds like some serious work….but if it lets me know flushing is working…..
Just hard to believe the ‘circuitry’ of the flushing system would flush the entire motor yet exclude the telltale.
Any and all advice/experience with older (hmmmm….should I say vintage?) Honda outboards is greatly appreciated. Thanks!
 
I only ever use a barrel to flush my 1999 130, the Honda does not seem to work well off a hose, lots of owners have this experience. If it’s pumping well in use, I wouldn’t worry about it not flushing well on the hose. Have you checked the thermostat?
 
What NSDON says.....Probably.

I don't know because I've never worked on a 90A model.

Having said that, the flush valve (item 5 in link) and the pressure relief valve ( the other item 5 in link) don't look too tough to get at IMO and just cleaning them up would probably be all you'd need to do.


But if you're not up for digging those out, you certainly won't like my next suggestion.

In behind the water jacket (item 14) is typically where evil "crusties" build up and cause blockage problems with cooling passages in the block. Again, I don't know but just making the suggestion because I've seen cases of that occurring with other "experienced" outboards.

Good luck.
 
Yes, it pees well when running ….the concern is it is running in salt water! I want to know that the entire motor is being flushed after use with fresh water when it is appropriately attached to a hose. Isn’t that what the flush port is designed for???
After seeing the video DCV made on his BF90D I am inclined to think the flush port valve (and possibly thermostat) is not operating correctly. Guess I will have to play marine mechanic instead of fishing.
Still hoping someone who has experience with a 1998 BF90AW to share whether or not it peed when flushed with a hose . My 1999 BF90A certainly did.
 
Still seeking clarification……
It seems to come down to water path through the cooling system under two different conditions….running and flushing.

When running, water flows from water pump up to thermostat. If thermostat is closed, it flows out exhaust ports and out telltale. If thermostat is open, it flows through head/block then out exhaust and telltale.

When flushing, water flows from hose, through flush port valve, then through head/block (if one is to believe flushing is accomplishing anything,), then out through exhaust and telltale.

The question is….after water flows through flush port valve, does it have to pass through thermostat or does it pass directly into head/block?

If through thermostat, I can see that would require the thermostat to be open to flush head/block. This would require flushing immediately after running while engine is still warm. But it seems even if thermostat closed, water should flow through telltale.
If passing through flushing port directly into head/block, fresh water would flush head/block whether thermostat is open or closed. Then pass through exhaust and telltale.

Either way, if my thinking is correct, water should be flowing out telltale when flushing. On my 1999 BF90A it definitely DID!
On my ‘new’ 1998 BF90AW, it does NOT. Which seems to indicate either flush port valve and/or thermostat are not operating properly.

For anyone running in salt water, these questions are critical! Proper fresh water flushing or a quickly destroyed motor…..not a tough choice. For those who have their boat on a lift, flushing while running with a barrel, muffs, etc simply is not an option. Attaching a garden hose to the flushing port is easy and clearly described in the manual. Hard to believe Honda would recommend flushing if it accomplished nothing.

Please let me know if this makes sense or correct me if anything doesn’t. Thanks!
 
I can’t comment on your major questions but having flushed several different Hondas (in a barrel), a 90 (2000?), 130, two 50’s, and a 5, all produced water out the telltale immediately prior to the thermostat opening . I’ve flushed mercury, old evinrudes, etecs, and Yamahas of various sizes and ages, all produced water out the telltale immediately prior to thermostat opening. I had a 90 mercury 2stroke, a 1998, for 10 years and only used muffs to flush. I’ve only had problems using muffs on the Honda.
 
The pump pushes water UP into the bottom of the engine block. Water is then diverted immediately after entering the block to the tell-tale bypass passage. You have a good pee stream with engine running so we know that bypass passage is clear.

But a blockage or even a partial blockage ANYWHERE above that bypass might prevent enough flow, while flushing, from entering the bypass and exiting the tell-tale.

I guess that you could just remove the Tstat, put the cover back on and try the flush port to see what happens. If the water then exits the tell-tale when using the flush port, it MIGHT prove that there's no problem with the pressure relief valve and no blockage from salt buildup or a rogue piece of pump impeller inside the engine.

With the stat out,.you could test it's operation in a pot of water on the stove and get some information that way. Or, just replace it with a new one.

Bottom line is that there's not much difference from the 1998 and 1999 model 90hp that I can see. The tstats and the water jackets are the same part numbers for both so your replacement outboard should probably "act" like the one you had previously..
 
Thank you for the reply! I checked the flush valve and housing this afternoon. Really quite clean. Also checked Tstat. Also clean. Remember, it is a freshwater veteran.
Did not test Tstat function …but will replace. Tomorrow I’ll have to try just removing it and replace housing….then see if that changes flow through telltale.
I will note this….i could feel and hear substantial flow through the flush hose and valve. A LOT of water flows out of the intake holes and exhaust….but not a drop through telltale.
Just can’t wrap my poor old brain around this issue.
 
Well, the water from the exhaust will be coming from the cylinder head. The water exiting the water intake screens will be coming from the block....backwards....so to say.

I have extensive experience with fresh water lake outboards and believe me, they can get mineral buildup and debris blockages that can be almost as bad as salt water. Especially if it's sole operation is in a "hard" water reservoir.

Minerals LOVE the heat of a surface inside an engine to cling to. It's known as "plating out".

And grass and twigs along with pieces of old impeller can get wedged into very inconvenient places. That's why, on an old engine, inspecting and cleaning behind the water jacket can really improve cooling and often solve a problem.

While you have the tstat removed, do some "backflushing" with that powerful water you say you've got.

Use a rag as a plug to block off passages inside the housing as you flush a particular passage to help boost the hoses' power. Mo powa mo better. ;)

It just might push something out in there. Although, it's best to do that with the pump removed so it has a path to exit.

Good luck.
 
OK….an update on diagnostic efforts…..
I had removed and checked both flush valve and thermostat. Both were very clean. Applied a little o ring lube to flush valve grommet and o rings. Reassembled. Running hose wide open through flush port. Could feel and hear water running. Pouring out intake holes as well as exhaust. Not a drop through telltale.
Ran a weed eater line through pee tube all the way to the T nipple on water jacket. Clear.
Removed Tstat to take closed Tstat out of the equation. Ran water again ….same results. Water through intake holes and exhaust, but nothing through telltale.
Removed flush port valve to take poorly opening valve out of the equation. Ran water again….same results. No peeing.
Replaced flush port valve, but not Tstat. Put muffs on to try to somewhat block intake ports and increase pressure in system. Ran water through flush port…..still no peeing.
Very briefly cranked motor while in that same setup ( flushing through port while somewhat blocking flow out of intake .
Actually got a weak stream from telltale!

Clearly, for some reason , this motor does not pee when flushed through port and not running.

Before anyone says just flush it in a tub or on good muffs……that is NOT an option in my situation. Normally I keep this boat on a lift and there is no way to flush it other than through the port. My 1999 peed 8’ stream when flushed through the port and not running . I find it hard to believe this 1998 wouldn’t do the same. Just don’t know why.
Flushing is CRITICAL since I boat in salt water. I need to KNOW the entire motor is getting flushed. If it is not peeing….how do I know? Even if Tstat is still open ( or removed!) it doesn’t pee. Doesn’t make sense.
Very frustrating…..
 
The pump, when in good shape, is VERY powerful. Probably more so than your hose pressure. You probably got a bit of a pee when you ran the engine because the pump was able to overpower the flow coming the opposite way from your hose plus have enough "oomph" left over to create a dribble.

The backflushing from inside the tstat cavity and using a rag to plug the adjacent passages to increase water power is a good technique to use for dislodging debris like twigs, weeds and old impeller pieces. It could make a difference.

I agree with you that the 98 should flush the same as the 99 for no other reason than that they are both essentially the same outboard.

I'll say it one MO time and then I will stop.
There's a VERY REAL possibility that there's a blockage behind the water jacket inside the engine block. A for sure pain in the keester to check that out but....well......
....WHOOP, there it is!

Good luck.
 
I will note that all the part numbers for water jacket cover, gaskets, thermostat, flush valve, etc, etc. are identical for 1998 and 1999.
So what is causing the 1998 not to pee on flush when the 1999 did? Both pee well when running.
Would replacing the entire water pump possibly reduce the retrograde outflow through the intake during flushing….possibly increasing the pressure above enough to have it pee? The 1999 pump had been…I don’t know about the 1998.
If I just could be sure the entire motor was being flushed (albeit while Tstat is still open) even though it wasn’t peeing…..I’d be happy, put boat and ‘new’ motor back in the water, and get back to fishing.
SWFL has an extremely high salinity. My perfectly running 1999 succumbed to corrosion despite good care for the last 11 years. But the first 15 was also spent here and who knows what care it really received. So flushing is right up there on my maintenance list. I’d sure like to keep this freshwater beauty running for a long time here in the salt!
 
Sorry Jgmo…..posted before I saw your reply appear. I hear you on the jacket cover. Lot of work, not to mention a $42 gasket, but certainly worth it if it straightened things out. What I can’t wrap my mind around is that the nipple for telltale tube is low on jacket. If it pees (through that nipple then out) when running, it would seem channel inside jacket ought to be open. If it wasn’t peeing at all, removing jacket would be clearly necessary.
Sure wish there was a resource showing paths of water flow in this motor. Might help make sense of it.
What do you think about my water pump thoughts? Worth rebuilding and possibly reducing retrograde flow through intake?
 
Wouldn’t hurt to do the complete water pump kit.

Before or after the new kit, maybe try a long vinegar flush in a barrel, I’ve used four 4 liter jugs of food grade vinegar and run it for 15-20 minutes at 1500-2000.
 
Lunasea said:
Sorry Jgmo…..posted before I saw your reply appear. I hear you on the jacket cover. Lot of work, not to mention a $42 gasket, but certainly worth it if it straightened things out. What I can’t wrap my mind around is that the nipple for telltale tube is low on jacket. If it pees (through that nipple then out) when running, it would seem channel inside jacket ought to be open. If it wasn’t peeing at all, removing jacket would be clearly necessary.
Sure wish there was a resource showing paths of water flow in this motor. Might help make sense of it.
What do you think about my water pump thoughts? Worth rebuilding and possibly reducing retrograde flow through intake?
Click to expand...
May I suggest when your running water thru your flushing port, take a can of compressed air and blow thru the tell tale hole, myself I use my wife’s compressed air for her computer she’s always asking what happened to the air for her keyboard I say I don’t know, hope she’s not reading this??!!
 
While I typically never argue about doing pump replacement (cheap insurance), my thoughts about why it doesn't pee when flushing is because there COULD be a blockage in the jacket interfering with flow that is.trying to travel in a direction opposed to the pump.
I could be wrong....often am.
 
Well, I believe I might have an answer. Pulled the lower unit today and found some significant issues. Still won’t know if they would cause the ‘no peeing on flush port’ until I reassemble tomorrow. Seriously happy I decided to investigate the water pump …..couldn’t believe it was moving water at all. Impeller was like a melted rock….looked like it was the original from 1998 ! Also found the grommet on top of pump housing that seals the intake tube was broken and useless. Fortunately had found a genuine Honda full rebuild kit on fleabay (for a good price) that arrived this afternoon. Got everything cleaned up and rebuilt. Would have reassembled lower unit and tested….but had to help a friend with his boat wiring.
Sure seems that these two findings might explain ‘no pee on flushing’. All the hose water was simply running out the bottom end…so not enough pressure to run out telltale. Fingers crossed that repairing them will solve things. Should know more tomorrow……
 
Agreed. But it's good you recommended he check it out.
Another testimonial about doing the pump, gear oil, plugs oil and filter on a "new to you" outboard.
I might also go with valve adjustment but that's usually a bridge to far for most.

It also goes to show just how well a totally wiped out pump can still move some water.
 
Last sentence is so true! Just for fun, I’ll try to post a picture….
Definitely a rock. The vanes don’t flex at all. Yet its shape still moved water!
 
My theory might not pan out…..
Decided to test more before reinstalling lower unit. Removed Tstat and flushed through port while blocking open end of intake tube.
Water poured through exhaust cavity, but still did not pee. Hard to know if the body of lower unit would reduce some of the pressure loss through exhaust. Maybe I’ll try to shove a rag in the cavity to see what that changes.
While it seems unlikely that scale would be causing this issue, might as well go through a 4hr flush with CLR and a pump while lower unit is off. Other than removing water jacket, I’m running out of ideas (and patience)
If the identical 99 motor does…..there MUST be a reason the 98 doesn’t. Just unable to determine exactly what!
 
May be bits of rubber from that impeller around and clogging something just enough to cause your hose issue.
 
Well, I do have additional findings to share.

I ‘mostly’ blocked off the midsection exhaust cavity with a couple of rags and blocked any retrograde flow through intake tube with my finger.

Lo and behold…..it peed!

I feel it is safe to conclude that internal passages are open and IF sufficient resistance to outflow through exhaust and newly rebuilt water pump ….it will pee on flush port not running.

I also got the thermostat housing off on the 99….wondering if it was stuck open and allowing it to pee not running whether motor was cold or hot. Found it to be closed. Seems to contradict the theory that Tstat must be open.

What remains to be seen is if rebuilding the water pump and reinstalling lower unit will indeed result in enough such pressure. Stay tuned…

BTW…..I decided to bite for some CLR and a cheap pump. Felt I might as well do a 4 hr descaling flush while I have things apart. Having come this far, it certainly can’t hurt!
 
Well, for those who have followed this saga…..I can share some great information.

Completed 4 hr CLR flush and then flushed with clear water. Little to no sediment noted in tub. Freshwater motor is a good thing.

Reassembled lower unit (with completely rebuilt water pump) onto motor.

Flushed with hose through port while Tstat was still out of housing. Peed strongly, as well as had some flow through exhaust and intake holes.

Replaced Tstat (new and CLOSED) then flushed through port again. Same result! Peed strongly with also some flow below.

Then ran motor in tub. Peed strongly.

Safe to say, all this effort has been worth it. The 98 pees now pees exactly like the 99….whether running or not running. SUCCESS!

Obviously folks will have to draw their own conclusions on their motors. This addresses Honda BF90. But I have to wonder if something might actually not be quite right on motors that don’t do the same. I do admit that seeing it pee while not running and Tstat closed still doesn’t definitively answer if entire motor is being effectively flushed. At the dock, I will still try to be quick about flushing immediately after running in salt water. Not to mention doing a long CLR flush with Tstat removed.when boat is pulled. Certainly can’t hurt!
 
I gotta say I agree with JGMO the best water pump on a new to you motor is the one you installed yourself. I flush my 2013 BF 200 that sees only salt water use as often as possible, and I change out the water pump about once a season, even though the old one usually looks pretty good. I figure If I have it apart, and a new pump is sitting there, just do it. Peace of mind.
 
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