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1997 BF90A - Sufficient Cooling Water? No noticeable water out center of prop.

A

AlphaBob

New member
Good Morning,

This is my first post on this forum and I'd greatly appreciate any comments on the video in the link below. Specifically, the video is a test run of my 1997 Honda BF90A: new water pump, thermostat, flush and pressure-relief valves. Everything looks OK, EXCEPT I'm thinking that water should be coming out through the center of the propeller. And, I can't really see any water coming out anywhere except the telltale stream. But, its hard to tell for sure because the muffs are spraying water around the bottom of the foot, so there may be some water dribbling out down there.

https://rumble.com/vem8tz-1997-honda-bf90a-no-water-out-the-exhaust-is-this-ok.html

When I run the engine as pictured, the thermostat cover gets to hot to hold my finger on - I don't know if this is a good sign, or a bad sign. Related, when I run the motor with the flush hose connected (hoping this isn't a bad thing to do), the thermostat cover stays cool. My concern is whether the water is completely circulating inside the motor. Although, when I opened up the thermostat and relief / flush valve passages I did not see any obstructions - just ordinary light corrosion.

Is it safe to take this out for a test run?
 
First, take that muff and squeeze the metal piece that keeps the tension on the muffs in a vice. That should cut down the amount of loss.

My next move would be to attempt to figure out why you have water coming from the flush port.

You say "new water pump". Does that mean you replaced the impeller or the entire assembly?

I would say heck no on the test run. You've got some work to do here.....
 
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Some outboards have some holes on the gearcase that need to be taped shut when running on muffs. I don't know if this is one of them...maybe Alan can tell you.
Just throwing that out there for discussion.

Good luck.
 
The 90's work on muffs OK, in my experience anyway. As mentioned, I did discover that the type our OP is using works MUCH better with a little extra tension holding the cup in place. Easily accomplished with a little squeeze from a vice. -Al
 
Furthermore, I don't know of any Honda outboard that should be run with the flush hose attached to the flushing port, if that is what you did - not good!
 
chawk_man said:
Furthermore, I don't know of any Honda outboard that should be run with the flush hose attached to the flushing port, if that is what you did - not good!
Click to expand...

That was one of my questions. I did run it briefly using only the flush hose. It's possible that I burnt up the brand new impeller (I'm guessing). One of my next steps is to run it in a barrel so that the water intakes are not pressurized. Using this approach will demonstrate whether the water pump is working - by seeing if there is a stream coming out of the telltale.

Does anyone know how the water is diverted when the thermostat is closed? if its supposed to circulate inside the motor until it warms up, is that the possible reason that no water is coming out from the propeller? The problem with the logic is that where would the water go if its not coming out of the exhaust?
 
Alan Hicks said:
First, take that muff and squeeze the metal piece that keeps the tension on the muffs in a vice. That should cut down the amount of loss.

My next move would be to attempt to figure out why you have water coming from the flush port.

You say "new water pump". Does that mean you replaced the impeller or the entire assembly?

I would say heck no on the test run. You've got some work to do here.....
Click to expand...


Good idea on tightening the muff - the muff is a little long in the tooth anyway - I borrowed it from my son's boat. Regarding the water pump, its a metal housing (i.e. Mercury) water pump so it go a new impeller, key, all the gaskets including those on the vertical shaft seal assembly - also installed new vertical shaft seals. The stainless plate the forms the bottom of the pump was replaced also. I'm going to check the water pump by running the motor in a 55 - gallon drum filled with water. The telltale should indicate if the pump is running (I assume, but chime in if this isn't correct).
 
If you are lucky, you didn't burn up the impeller - but you must check it. Even if working OK now, that could be trouble down the road, IMO.

I don't know much about the BF 90, but on my BF 225, when you start up and the t-stats are not yet open, cooling water is diverted to a pressure relief valve near the bottom of the engine. The water pressure opens up a simple spring-loaded valve and the cooling water is diverted back into the water jacket. As the t-stats open, the pressure is reduced and the pressure relief valve closes.

OK, I looked it up. Your engine is a bit different - see parts 4,5,8,9 at:

https://www.boats.net/catalog/honda/outboard-by-hp-serial-range/90hp/bf90a3-lrta-2003/thermostat

The hose coming out of the #9 "spacer" likely goes straight back into the water jacket.

BTW - the telltale is not necessarily a reliable indicator of adequate water circulation. They can easily get clogged up, even if cooling is fine. For a definitive test, use a heat gun on the manifolds. Not sure what the spec is for the BF 90, but on the BF 225 it's 160 F.
 
Thank you very much for all the good comments and suggestions - I think I've verified that I have sufficient cooling water for a test run. I separated the rubber hose between the water pump output and the cooling jacket input and connected a garden hose to the water jacket side - this static test allowed me to verify that water is freely flowing thorough the cooling passages and out the bottom of the motor as expected. You can view the video of this test here:

https://rumble.com/veqvkj-test-2-1997-honda-bf90a-cooling-water.html

Next I did a heart / lung bypass dynamic (i.e. engine running) test. The muff was installed on the foot to feed the water pump, and separately the water jacket was fed with a different garden hose. The temperature of the thermostat housing stayed in what I believe to be the normal operating range and the water pump put out a good volume of water. The water pressure was extremely low, but again the volume was high. You can view a video of "test #3" here:

https://rumble.com/vertpx-test-3-1997-honda-bf90a-water-pump-output.html

I suspect that the water pressure is low because the motor is idling. At higher speeds the centrifugal force holds the impeller fins tightly to the pump walls and the dynamic water pressure of water being rammed into the inlet increases the pressure inside each wedge shape and further enhances the pump efficiency. This conclusion is based on subsequent inspection of the water pump - everything looks fine - even no evidence of leakage out the top of the pump, and the connection between the pump output and the vertical water tube inlet (connected when the foot is bolted back on) is tight.

If any thoughts come to mind, or if anything jumps out, don't be shy about commenting~
 
I haven't seen any explanation regarding the water coming from the flush valve. I don't know this engine as well as some others, but the water coming from the flush valve leaves me wondering about check valves not holding, or stuck, preventing the flow of water through the engine as designed.

The logic being, I think that flush valve diverts all of the incoming water up into the engine - preventing it from back feeding the water pump. If a valve in that system were to stick for instance, it could theoretically prevent water flow from the pump? That being the case, I would have to do some investigating....
 
Thanks for reminding me! I meant to mention this in my last post - the flush valve stopped dripping. It was a new valve and I'm sure that it has just gotten knocked out of alignment a little. It appears to have reset itself after I used the flush port the last time. Good catch on your part - thanks again!
 
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