BF135 ongoing saga. Over heat at full RPM only

Hi Guys,

I have a pair of BF135's on a Cat that I have had many problems with due to buying this project boat "as is". Thankfully to date all previous problems have now been sorted ( thanks iang6766 ) and this is now my last known issue.

This last problem has me struggling again.... The port engine buzzer/alarm comes on and RPM drops back to almost idle when i run at full throttle only. If I key off and restart alarm goes off and i can run around as normal for hours unless getting back to full throttle and running for about 3 or 4 minutes again. In the past i suspected a wiring issue but this last weekend i did notice the overheat light coming on when alarm sounds. This alarm at full RPM's had been an issue for the previous owner and he eventually gave up after spending a heap of money, stuffing a whole lot of things up and then leaving it sitting for 18 months.

To date I have changed out complete water pump asms
Changed thermostats
Back flushed with various chemicals and water
Pulled the legs again today and loosened off the water pipe that goes up extension housing to the oil pan area- inspected the grommet. Couldn't remove the pipe itself but its not blocked. In fact it looks new from the outside. gromit is perfect
The engine pee's fine but it does pee a little less that the stb engine that has zero issues.
There is no obvious corrosion in anything I have pulled apart.
I have pulled all 4 temp sensors and ohms tested against the good engine fine
With all the flushing, back flushing and chemical flushes I have done over the last few weeks I have got no nasty stuff out of anywhere
Im working in Papua New Guinea so don't have ready access to a Dr H or Honda dealership
I have run a heat gun over everything when in shop running in a trough but no high temps, pee runs cool until the trough water get up in temp. In saying that the alarm doesn't go off in the workshop trough...
Thinking of putting back on the water and doing more testing but not sure where to start
Is there something else I should be looking at? Any advice whatsoever would be appreciated

Cheers

Hi Shane,
It does sound as if you may have a blockage of some kind in the cooling system. Most often this turns out to be debris from a deteriorated pump impeller.

If you haven't tried back flushing with full shop air pressure through the thermostat housing with the gearcase removed then I would suggest that before anything else.

In order for the air to do any good, you have to create a seal around the nozzle. I have an automotive cooling system gun that I bought online that has different sized rubber seals for the tip and hooks up to a garden hose. It also has an air nipple so I get the combined power of the air and water working together.

But, in the past, I have used just a rubber tipped air "gun" and use a wet shop rag to create a pretty good seal to help force the air into the passage I'm flushing.

The more pressure and flow the better. Some compressors have an adjustable regulator that you can use to dial up to around 125 or even 150 psi. I would max it out for this one chore and dial it back when done.

Good luck and I hope you get it figured out.

In addition to what Jimmy recommends, I don't know much about the 135/150, but I do recall that they have two thermostats that open at different heat ranges. Are you sure you have the right ones installed in the right places?

Also, have you tested the heat sensors?

Hi Jgmo,

Thanks for that. I have blown air everywhere but down the thermostat housings themselves. I even ran water via small pressure washer down there. I will give the air a go. Would love to see a chunk of old impeller fall out

Chawk,

Yes 2 thermostats and both are in correct positions. Even though new I checked them in boiling water and OK
With the temp sensors I have only pulled them ( all 4 ) and compared ohms on each to the good engine - cold only. No bad readings but perhaps bench testing cold not the way to do testing?
Think i'm going to try Jgmo's advise with the air then re assemble and put back on the water and pull temp sensor plugs once I can get the alarm back on to see what sensor is saying overheat.

Cheers

Try swopping the block temp sensor,it's the one next to the oil filter with a two pin plug, with the one on the sister engine. I have had a couple of these go out of range and set the overheat signal prematurely.

Actually, don't stuff around, just swop them all with the other motor and if problem goes to the other motor you will know it's a sensor .

Swapnostics is a good way to go since you have the other outboard.

I'm just going to throw this out there so you have the info in your tool kit for this....

Many people, including many techs, think that running an engine without the thermostats installed will have the engine running cooler all the time. And, they are right....but only to a certain degree.

I think we all know that running without tstats installed will have an engine running too cold. This affects combustion and performance negatively.

But the thing I want to point out here is that running an engine without the tstats can actually cause overheating!

The reason is the "bypass" circuit that the stats uncover when they are closed during what is called "rapid warm up". Each manufacturer uses a similar strategy for "reheating" the engine block to bring cold start temperatures up to "normal" or operating temperature by taking some of the flow from the cylinder head (the hottest part of the engine) and directing it back into the engine block in a sort of circular flow manner. Then, when the stats open, this recirculation path is closed off as it is no longer needed.

So, if the stats aren't installed, the rapid warm up flow is CONSTANTLY returning to the engine block through the unblocked bypass. At high rpm and high load, when the engine requires maximum cooling, the bypass is delivering unwanted heat into the engine!

I'm telling you this because I have seen this occur in engines that DO HAVE the thermostats installed but, for various reasons, they don't block the bypass circuit sufficiently enough to provide maximum cooling.

The most common reasons for this is that the wrong replacements were installed.

Another common issue is tstat seals that are improperly installed or are deteriorated.

Also, in an engine where corrosion has taken metal from the housing, the stats or seals or both no longer fit properly.

Now I'm not suggesting that all this applies to your problem. I don't know this outboard or how the thermostats are configured. I just wanted to make sure you know this and maybe you could spot something out of place or not quite right as you put her back together.

Good luck

I'll throw out one more reason for an engine to run hot at full loads and then I'll shut up....until I can think of another ;>).

A lean burn condition can cause an engine's combustion temperatures to be excessive. This might translate into overheating. A close inspection of the spark plugs is a good way to get an idea if a lean condition has been occurring.

I don't know how likely this is in your case. The comment that you made about the pee stream being less on your problem outboard still makes me think of a blockage of some sort. I'm just brainstorming this aggravating condition and want you to have as many ideas as we can come up with.

I hope you find and slay the dragon!

Thanks for the advice iang6766 and jgmo

Going to put in the water this afternoon and try and get some more time on the water and pay more attention to when the overheat alarm goes off. One thing i did notice after legs off and flushing again (and blowing high pressure air down the thermostat housings) ...is that the "bad" engine does appear to pee a little better than previous times, it was never what I would call weak just not as good as other engine.... Even timed how long it took to fill a small container and both engines are peeing at same rate. No gunk came out of anywhere... but perhaps something has moved.

I did revisit the thermostat location and made sure that the new genuine Honda ones I received were correct temp. They are 50 and 60 degree and are in the correct locations. There is no corrosion or anything suspect about the thermostat seats, plastic spacer block or gaskets.

I have swapped all 4 temp sensors to the good engine. I was going to remove the thermostats and give that a try but understand Jgmo what your saying. We used to drill small holes in automotive thermostats in the belief that this would help with circulation... or remove to counter overheat situations

I need to have a look at the cavitation plate in relation to the water at speed also. Engines possibly 1 notch to high judging buy how its sits.

Will update after the weekends re testing

Cheers

I'll be interested to hear your results,these engines generally don't give problems with the cooling systems

Ha ha, I still see people drilling holes in thermostats. And, I do think that if there is a trapped air issue due to poor filling and bleeding procedures (closed, pressurized systems) it's been known to work.

But, today's after market parts stream is so bad it has become universal knowledge to stick with OEM tstats whenever possible.

Hope you have a GREAT test drive!

Guys,

Just letting you know I was unable to get on the water the last 2 weekends due to the weather and had work travel during the week... Will report on outcome of test drive this weekend

Cheers

No hurry....we wait patiently.

Hi Guys,

Well I finally managed to get out on the water this weekend for a few trials...
Bought a mate along so I could monitor the pee stream etc while he drove

Alarm and temperature light still coming on Port engine even though swapped all 4 temp sensors over with the "good engine"
A little more detail on the fault now I have more feedback . If I throttle up to 5300 +/- RPM's the alarm/light comes on after about 1 1/2 to 2 minutes and goes into backup mode - this clears within seconds and resumes to normal operation with no alarms / lights. The engine pees fine all through the rev range. I can run the boat at 5000 RPM for extended periods and no alarm/ lights. Soon as it hits the 5300 mark and kept at that rev range for around 2 minutes alarm / light comes on again.

The pee stream while underway never gets warm. In fact it feels very close to the sea water temp - currently 26C /79F over here.

Now the strange part to all of this is we got brave and decided to load up the good engine a bit more to see if that would also alarm at any given speed , it wouldn't even up to 6000 RPM. Then we ran both engines to 6000 ( full throttle) expecting the bad port engine to alarm after the usual 2 minutes +/- and it didn't! We tried this several times and got the same result. At full throttle / 6000 RPM no alarm. We didn't run too far or too long at that revs as it seems excessive especially standing beside the motors while they are both screaming but it certainly appears that the fault is only around the 5300 ish rev range.

As usual any further advice or suggestions will be appreciated

Cheers

This is a real headscratcher. One thing that came to mind after reading how the two engines performed at 6000. This sounds like it could be related to harmonic vibration. Engines vibrate at different frequencies as rpm is raised and lowered. I'm wondering if you have a connection in the temperature warning system that's sensitive to the vibration set up in that 5300rpm range?

I mean, it doesn't seem to be actually overheating so it's got to be something weird like that.

Have you tried swapping the ECMs, this is not making any sense at all? DrH would help a lot to see which part of the engine is overheating if it is.

Hi Jgmo,

Yes I agree its a difficult one and now that all seems to be OK at 6000 has me really stumped. I will revisit the earths at the front of the engine as they were a bit green but were cleaned up back when i was chasing the MIL light problem. Besides those earth's every other wiring connection and plug on the engine has been immaculate. Main looms are all new. With the harmonic vibration I guess its possible that a wire is breaking down... I do have a slight vibe at idle and it resonates through the alloy hull at trolling speed but nothing noticeable at high speed - although it would be hard to notice i guess.

Hi iang6766,

I changed ECMs back when i was chasing the MIL light problem you sorted for me with the new little 2 lamp clusters. I'm not sure now what ECM I have on what engine so that will be my next job. I ordered a "Honda Marine Diagnostic system" of some ebay seller with 200 + sales of the product last week and should have before the weekend. I have seen lots of debate on it vrs the DR H but worth a shot for the price ( around $ 200 USD ) if it gives some sensor outputs.
I am still suspect on the overheating side of things. Everything tells me its not overheating but not yet convinced otherwise. The water coming out of the pee tube is suspiciously cool and wondering if something is allowing it to bypass so i'm only seeing water almost direct from the leg vrs after its circulated in the block.
I hope the HMD will point to what temp sensor is telling me its hot. Is there one sensor in particular that is set to "go off" at a lower temp than others? Thinking about Yamaha's I have had previously - when plastic bag or something got around the water intakes alarm would always sound very quickly...

Cheers

Not sure what a "cold" pee stream would point to. I assume that you have compared it to your other outboard. Is there a significant difference between the two stream temps?

The tell tale circuits are "bypasses" and aren't intended to pick up a lot of heat but I agree that they get warm normally.

You. might try feeling the stream as the engine is switched off. You have to be careful doing this because it's my experience that as soon as the pump stops, the stream almost instantly gets very hot. If you have sensitive skin, you probably shouldn't even try this little experiment. I really can't say why this phenomenon occurs but I noticed that it is very consistent on the outboards I've worked on with healthy cooling systems. I have speculated that what is happening is that the water column that is in the block drains back and out of the tell tale but I'm not absolutely sure.

The only reason I suggest it is it may be another comparison you can try between the two outboards.

I was going to say that swapping the ECM's is a good idea but I see you did that already.

Hi jgmo

Understand on the pee and yes cool water from both engines stream while underway. Was just something i had thought about as doesn't make sense if truly overheating and pee stream cold. Both engines so must be normal

On the ECM i probably didn't explain properly. I have changed them around in the past while chasing previous faults so not sure if original ecm is with original "bad" engine now that this overheating fault has shown. I will swap ECM's and report back.

Cheers

Hi Guys,

Sorry for the delay in reporting back but weather here has been rubbish.

So back to the on-going saga. As recommended I previously changed all 4 temp sensors with the good engine - this did not change the fault so this weekend swapped over the ECM's. Same problem still exists on testing. Overheat light comes on and constant alarm. This still occurs at around 5300 - 5500 rpm after maintaining same rpms for a minute or 2. Alarm clears within seconds and can then resume without issue . I did receive the HMD disc and cable and have tried it but its been frustrating as weather has been rubbish, cable is 1 1/2 meters shorter than would allow me to sit in the cab...so trying to keep the laptop out of the rain / ocean mist, trying to manhandle a beer while having a mate drive... along with alarms going off while laying belly flat on the deck does not make for an enjoyable trip

Anyway this HMD did allow me to read 3 of the 4 temp sensors. They all showed various steady rising temps with max temp on sensor 1 showing highest temp of 80 C / 176 F. When I did same testing on good engine temp sensor 1 ran about 5 - 8C degrees cooler. Not a lot of difference.
One thing i did notice the other day when I first hooked up the scan tool is that If I unplugged the various temp sensors they would in turn throw the MIL light , set a hard code as well as the buzzer and temp light. I'm presuming the problem I have means I don't have a broken wire or bad connection on any sensor wiring as I never get a code or MIL light on when the normal 5300 rpm overheat occurs.

So is it possible that it is actually overheating while only showing 80 Deg C? I did note that sensor 2 and 3 were considerably cooler... could this alarm be set off as too much variance between sensors?


Any more ideas guys? I cant do too much with it sitting in its berth and cant replicate the fault when its on land running in a bucket...

Any suggestions appreciated as usual

Cheers

Hi Shane,the temps you are reading are normal, the block temp ECT 1 can get as high as 103 deg C without activating the alarm and it's normal for the others to hover around the 60 deg mark. Is the alarm and temp alert light activating at the readings you mention? If so this is really weird because they are exactly where they should be. If you can, get the alarm to sound and try and keep it sounding while you go into the DTC faults , it may tell you something whilst the alarm is actually active. Honda diagnostics are not the best but with a bit of stuffing around you can usually figure out the fault. The other thing you can try is to take a data snapshot whilst running with alarm activated and send it to me by email and I can have a look for you and compare with run files that I have for those motors.

Hi Shane,
I wrote a long reply and accidentally deleted it. But, on reflection of typing it all in again I think I'll hold off for now. Because, Ian has given you some excellent things to try so let's see what happens with those.
Just letting you know I'm still watching and interested.

Man! I feel your pain!

Thanks Guys

iang6766, Yes the alarm and temp light does come on at those temps. Highest sensor # 1 got was 80 +/- C while others were considerably lower . When I tried again at 5300 rpm and went into the DTC screen nothing showed while alarm and light was on... So doesn't seem to be setting hard code. But when i was "playing" at the berth earlier i could get a DTC by disconnecting each sensor - this would also activate the MIL lamp and codes then had to be cleared. What I do need to figure out is does whats showing as sensors 1 , 2, 3 on my laptop equate to 1,2,3 sensors on the engine. As mentioned before the scan tool only shows 3 of the 4 temp sensors so perhaps "missing sensor 4" on my laptop is the one that's playing up... . I will try and get some screen shots at about the time of the alarm going off and post. I have really only had a quick play with the HMD but couldn't save any data to review later... I will spend more time on it.
One question: are those 4 sensors all set up with the ECM to activate the overheat alarm at the same temperature ? Could alarm potentially be set by any of the 4 sensors at above say 103C....Or is one sensor / ECM reading set at lower activate temp. Was wondering if sensors are in wrong locations as previous owners have done allot of mucking around. When I swapped sensors I just swapped 1 for 1 - same locations.

Thanks for all the great advice iang6766 and jgmo. I couldn't have got to this final ( but frustrating ) stage without the help from both of you

Cheers

I wonder if you might have some RFI (radio frequency interference) causing this. If you have spark plug wires that are breaking down you they will "leak" RFI. COP (coil over plug) ignition can do the same thing but it's much easier to change out a set of wires than to start replacing coils. An oscilloscope is the preferred tool for diagnosing this but not something most of us carry in our hip pocket.

Another thing that causes the ECM to act goofy is when diodes in the alternator break down and allow alternating current to "ride" the DC signals. We call this AC "ripple" current. Happily, it is easily detected with a digital volt meter. You simply check your battery as you normally would to see what the charging voltage is. Red lead on positive terminal and black on negative terminal, engine running. The only difference is that the meter is set to the AC volts scale instead of DC volts. A reading of 0.50 volts ac or higher is definitely a problem.
Check at idle and at about 2500 rpm. I'm not sure about taking it over 3000 because ripple should show up at the lower speeds.

To answer your questions, all the temp sensors are the same part number. You obviously don't have a genuine DrH, to identify sensors, disconnect one at a time noting on your active DTC what number sensor is showing open circuit, that way you will know which is which. The temp sensor nearest to the oil filter is the block temp, this is the one that should read a lot higher than the others.

Hi jgmo

I guess its going to mean getting into all of these kind of details to get to the bottom of it. Easy enough to check the battery re the AC current and perhaps worth changing over the coil packs too. Haven't changed the plugs - as told they were new when i purchased so worth doing also - or at least inspecting them.

Hi iang6766

I just checked the online parts book re "all temp sensors are the same" and one of the 2 sensors in the thermostat housing differs from the rest. Block sensor , Exhaust top sensor and one of the sensors in T/Stat housing are listed as 35673-ZY3-003 while the second sensor in T/Stat is listed as 35673-ZW5-003. I m not sure if this is a typo or what

No I don't have Dr H, Its some mickey mouse copy but yes I will need to pull all sensors and confirm engine locations jive with the laptop locations. I should have paid more attention when pulling all sensor plugs previously. I will do more testing and report back. Hopefully with some screenshots

Cheers

Shane,
I love your no quit attitude!!

Your chaincase must have been replaced at some point, the old ones had all same sensors and then around 2007 they changed , the thread size being the difference, if you look at the correct year it should show them as the same with an offset diagram showing later numbers if chaincase was replaced, it's complicated, but long story short, resistance values are the same