Honda BF50D giving me fits..... (cooling issue?)

New here, just joined, but have been a frequent lurker.

I bought this engine on the cheap from a guy in the Tampa area, knowing full well it hadn't been well taken care of - what I call a "salty". I've had the head and the exhaust cover off, and removed all the crud. New water pump and t-stat. All passageways have been cleared of crud using a coat hanger and compressed air. Peeing like a champ. This is not the first one of these 40/50's I've done, but it is my first EFI.

Long story, multiple issues, but I believe my immediate problem has to do with the second water temp sensor, the one located by the oil filter (I suspect this is more of a block temp sensor?) After a LOT of messing around, I figure something is going on here. With the engine on muffs, and with plenty of water available, I'm getting an alarm from the control head (which is an old style, and works fine with other older motors) when the engine is run at 2k for a few minutes. It will idle forever.

The 2 temp sensors are identical, have the same part number. I've swapped them to see if the problem remains and it does. However, if I remove the second sensor from the block and let it hang by the wires, there is no alarm. It would seem the block is getting hot enough to cause the sensor to set off the alarm?

The water temp coming from the indicator/pisser does not seem that hot. You can leave it running on your hand. I get no sense that the engine is hot.

Oil and filter are fresh.

Ideas?

Sorry to wander, but I wanted to include as much detail so as not to leave you wondering what's been done.

Thanks so much!

First thing I would do is run the motor in that water, running above idle on a hose often causes an overheat because the water flow is aerated.

When you say..... you "remove the sensor and let it hang by the wires"
...is there water coming from the port it mounts in?
And, if so, have you tried measuring the temperature of that water?

It could be something as simple as a connector or wiring problem at the sensor that you are unknowingly "fixing" temporarily when you let it hang like that.

If no water is leaking (gushing really) from the port while hanging the sensor then that may mean you have more crud to remove inside the block.

I agree with Ian about running it submerged instead of on muffs. Test tanking is way better for accurately troubleshooting cooling and water pumping issues.

Good luck.

iang6766 said:

First thing I would do is run the motor in that water, running above idle on a hose often causes an overheat because the water flow is aerated.

Click to expand...

Aerated a good thought. I can do that. I have a barrel for that reason. It's just easier to run them on muffs. Will do that today to eliminate that possibility. Thank You!

jgmo said:

When you say..... you "remove the sensor and let it hang by the wires"
...is there water coming from the port it mounts in?
And, if so, have you tried measuring the temperature of that water?

It could be something as simple as a connector or wiring problem at the sensor that you are unknowingly "fixing" temporarily when you let it hang like that.

If no water is leaking (gushing really) from the port while hanging the sensor then that may mean you have more crud to remove inside the block.

I agree with Ian about running it submerged instead of on muffs. Test tanking is way better for accurately troubleshooting cooling and water pumping issues.

Good luck.

Click to expand...

The issue that's mystifying me is regarding a second temp sensor, located down near the oil filter on this EFI engine (at oil filter's 1 o'clock). The older carbed 40-50's don't have this sensor. This second sensor is installed in a "dry" port. There is no oil or coolant circulating though it. Inside is shiny, so it's easy to see this is by design. Nothing plugged. This is the sensor I'm leaving out, hanging by the wires, to eliminate the control head alarm.

Thanks for your thoughts! -Al

Hi Al,

I'm not familiar with that engine so I'm asking questions, not implying I know it's any different than you say it is....but....

Are you using the shop manual and does it specifically say that sensor is sampling something other than water?

When you pulled the top sensor, was it dry behind that one too?

I'm curious because they are, as you said, the exact same part. And they are both mounted with an Oring as you would expect a water temperature sensor would be to prevent leakage.

Last question....
I know you said that you coat hangered all the crud out but I'm wondering if you pulled the water jacket covers when you did?

Just trying to help and maybe learn something myself here. I'm thinking about buying a 50 Honda EFI to repower an aluminum semi V.

Hope you get it figured out and I'll be reading your updates.

Thanks,
Jimmy D.

Jimmy,

I'm happy to share my experience in exchange for your thoughts. I'm convinced all this is going to take is the right idea or to be pointed in the right direction....
I'm retired, and have kind of an unusual hobby that keeps me busy/in mad money. I like bringing back dead Honda 40's and 50's. They're all I work on, other than an occasional Honda 90 for friends. Have been doing this for several years, so pretty familiar with the older engines.

That in mind, to answer your questions, no, not using a manual as a rule, but I do have one for the older "A" motors (rarely needed any more). Haven't bought an EFI manual....yet! Top temp sensor, t'stat housing, exhaust cover (water jacket cover), and head have all been removed and carefully cleaned/blown out. Thankfully no advanced corrosion was found. Nothing needed to be replaced (not always the case).

Regarding your purchase thoughts, maybe because I was raised in the old school, I prefer the carbed engines for their simplicity, even if they do force you to use a choke. WAY less complex than an EFI....

Thanks! -Al

iang6766 said:

First thing I would do is run the motor in that water, running above idle on a hose often causes an overheat because the water flow is aerated.

Click to expand...

Nice try, but not the solution we're looking for here. Does the same thing in a big drum of water, w/water level an inch or so above the top plate. (cut down 90 gallon trash can).

Thanks for your input. -Al

The other sensor measures block temp. One more question, when you ran your motor on a hose did you seal the secondary pick up under the cav plate above the prop, if not and you revved the motor you more than likely over heated and destroyed the impeller and possible the housing too, I have seen this many times.

iang6766 said:

The other sensor measures block temp. One more question, when you ran your motor on a hose did you seal the secondary pick up under the cav plate above the prop, if not and you revved the motor you more than likely over heated and destroyed the impeller and possible the housing too, I have seen this many times.

Click to expand...

I learned that fried water pump lesson the hard way too...

Thanks for confirming my thought regarding the second sensor = block temp. Located so close to the main oil galley, guessing that oil temp in play as well.

-Al

Well...I used to think carbed engines were less complicated too but I bet once you get used to EFI, you might change your mind.

You still didn't answer my question about whether or not the upper sensor was immersed in water or not. You see where I'm going.... I'm still not convinced that block sensor was intended to be in a dry hole. But, I'm probably wrong....usually am. [:>(

One other thought fer ya....
Did you go through the VST cooling system and verify flow through all that plumbing? A clogged tube there might set up some sort of "flow dynamic" that could disrupt cooling. I see this type of problem occur occasionally when heater cores plug on autos and disrupts coolant flow.

Good hunting!

Well...I used to think carbed engines were less complicated too but I bet once you get used to EFI, you might change your mind.

You still didn't answer my question about whether or not the upper sensor was immersed in water or not. You see where I'm going.... I'm still not convinced that block sensor was intended to be in a dry hole. But, I'm probably wrong....usually am. [:>(

One other thought fer ya....
Did you go through the VST cooling system and verify flow through all that plumbing? A clogged tube there might set up some sort of "flow dynamic" that could disrupt cooling. I see this type of problem occur occasionally when heater cores plug on autos and disrupts coolant flow.

Good hunting!

Sorry about the double post. I got impatient pushing buttons.
Anyway...
As to the VST, I would also pull that water jacket cover and "de-crud" in there if you haven't already.

VST plumbing has been apart and thoroughly cleaned. You can add that to the list of stuff mentioned already that I've had apart and thoroughly cleaned.

In an attempt to troubleshoot this cooling issue, the engine was started without the (top) temp sensor installed. This resulted in a virtual fire hose shooting from the side of the engine. Amazing amount of water coming from that small hole actually.

The "dry" hole the second temp sensor is located in was confirmed dry by lang6766 in note #9. There's little doubt it's water temp sensor acting as a block temp sensor. It's actually located in a section of the block that is not water cooled. All of the water passages in the block would be located further back, toward the cylinders.

Thanks for your thoughts, -Al

Hmmmm....
....well....
....Alrighty then!

Thanks Al.

JimmyD

Update from this morning-

I found a battery to fit my (very) inexpensive infra red temp gauge. When the alarm goes off, the area around the block temp sensor is just under 150 degrees (146-148 indicated). Oil filter in the high 130's. Other areas of the block all in the 130's (measured closer to the front of the motor). The water temp sensor area is about 135. When the engine was shut down, the t-stat was removed and found to be still closed.

I need to look further into what temp the t-stat opens at, and what temp these water temp senders are supposed to close/open, not sure which.

To satisfy my curiousity, the engine was run without the t-stat (save the sermons, I know this is generally a no-no, and why). Oddly enough, the alarm didn't go off, and the block temps were down just slightly. Pisser was running noticeably cooler.

Ideas and thoughts welcome! -Al

You might find the tstat temp stamped on it if you still have it out.
I obviously don't know what it's supposed to be but I'm guessing it's probably no lower than 180° and likely higher than that being it's an EFI engine. If this were a betting pool I'd go with 190° to try and win the pot.

So...with those temperatures, it sure doesn't seem it's overheating at all. Could this be a case of a faulty alarm circuit in the ECM?.....OR....

The fact it doesn't alarm with the stat removed, could it be an indication that you have a flow problem?

Flow is so critical to proper heat exchange. Have you ever shut the engine off while holding your hand in the pee stream? If you try it, be careful!
As soon as that pump stops pushing, the block transfers lots of heat very quickly into the slow moving water. It can scald you!

Okay, I have two suggestions left. Have you removed the cover on the port side of the cylinder head, the one the thermostat sits in? If you do, right at the bottom there is a slot for the water to exit that may be blocked, clean this all out thoroughly and blow with compressed air. Change the internal anode whilst you are in there. Secondly, when you say you fried the impeller by not covering the secondary pick up, did you replace the complete pump, because if you didn't I would suggest you do. The pumps have a tendency to distort in these instances and lose efficiency very easily.

Thermostat should be 60 deg C

iang6766 said:

Thermostat should be 60 deg C

Click to expand...

Whoops!

It's a 72c (converts to 161 f) supplied from the small stash of commonly used parts for the older engines that I use frequently/keep "in stock".

That's significantly warmer than the 'stat the newer EFI engine calls for - the 60c 140 degree t'stat..... and kind of a surprise that the older engines run warmer than the new ones?

Not completely convinced that's the whole story here, but we'll have a new (right) one in a couple of days. Another one of those hard earned lessons I guess.

Meanwhile, the lower unit will come off for a second look at that - including the water pump.

Thanks again! -Al

iang6766 said:

Okay, I have two suggestions left. Have you removed the cover on the port side of the cylinder head, the one the thermostat sits in? If you do, right at the bottom there is a slot for the water to exit that may be blocked, clean this all out thoroughly and blow with compressed air. Change the internal anode whilst you are in there. Secondly, when you say you fried the impeller by not covering the secondary pick up, did you replace the complete pump, because if you didn't I would suggest you do. The pumps have a tendency to distort in these instances and lose efficiency very easily.

Click to expand...

Sorry, missed this note on the first pass.

Yes, have had that cover off, but having second thoughts regarding how thorough I was in cleaning ALL of the passages. For what it takes, I'll revisit that. I do have a clean older block sitting on the bench that I can reference to make sure I'm seeing all of them.

Regarding the "lesson learned" that happened a few years ago, and yes, I absolutely tore that pump up, so everything from the bearing up needed to be replaced. Lessons like that can be so humbling....

Still on the "second thoughts", will be pulling the lower unit for another inspection of that, AND the pump, to rule issues there out completley.

Thanks much for your thoughts! -Al

UPDATE-

After double checking the cooling passages under the water jacket/exhaust cover (no problem found), pulling the lower unit to confirm all passages, including the tube leading up from the pump are clear, AND installing the correct 140 degree t-stat, I installed the motor on a test boat and took it out onto the lake. Starts and idles perfectly, but get the temp warning buzzer w/500 rpm throttle reduction in just a couple of minutes runtime. This at 3000 rpm or so.

To the only way to kill the buzzer is to shut the motor down and restart. Then it acts like nothing happened - until you throttle up.

I did check to see if the engine was making oil (leaking gas through the fuel pump) and it's not. The oil does seem kinda thin (dripping from the dipstick), though that could be my imagination.

Stumped.....

-Al

This sounds a lot like one that has the impeller vanes pointing the wrong way. You couldn't have done that to yourself could you?
I've done that before and I still struggle with second guessing myself when I put one together because it happened AND because I don't do a pump all that often anymore.

Not trying to insult you.....just sayin'

Trust me, any ideas very welcome at this point. Don't worry about insulting me. Worst case, I might get a chuckle out of the deal! Point being, not easily offended, especially by somebody trying to help.

I have to believe if I had done that (vanes pointed in the wrong direction on install), that these vanes are long and soft enough they would have flipped themselves, especially after today's run. I did make a "damn the buzzer" wide open pass for 2-3 minutes, hoping the problem would become apparent (or the motor would blow). Of course it didn't, but your mind makes you do funny things on occasion. Anyway, with the boat moving at speed and full rpm, the force of the water moving through the pump would have pushed the vanes back to the correct direction.

So there's that, and the fact the water indicator will shoot 20'. I'm pretty comfortable saying there's nothing wrong with the pump, or the volume of water getting to the motor.

Thanks! -Al

Ok....
Here's another brainstorm...

First, a question...
How much does this one vibrate? Many outboards vibrate a bit and others quite a bit.
Since that alarm goes off at varied rpms. I wonder if it could be a loose electrical connection that's sensitive to vibration? Harmonic vibration can do some strange things.

If this were equipped with an alternator I would also be wondering about that. When the diode banks fail they cause alternating current to "ride on" the dc current. This can cause solid state electrical modules to wig out at times. Happens on cars often.

Not sure about the magneto charge system though. I haven't seen it on those systems.
It's easy enough to rule out though. Just probe the battery posts with your DMM set to the ac volts scale. Any ac volt reading above 0.250vac (two hundred fifty millivolts) might be cause for checking the rectifier. I say "might" because I just don't know. But if there was another one you could plug in and compare, it might tell you something.

Just throwing out ideas.

This would be a smooth running engine, typical of Honda. Very little vibration. Charging system seems to be working well. Test boat has a digital volt meter that's reading a little over 14v. with no irregular flashing. Plus, the battery acts like a big 'ol capacitor that would filter out any weirdness going on until it got really carried away.

I don't believe this is happening as a result of vibration.

If anything, it seems to be tied to how long the engine is running at speeds over an idle. It seems like this is happening at 2-3 minutes.

I'm wondering if there isn't an error stored in the ECM that's causing this. I don't know a lot about that potential, so going to clear that and see what happens.

Thanks! -Al