BF135 ongoing saga. Over heat at full RPM only

Correction, off set diagram shows old with both sensors the same number, main diagram shows new style chaincase with different size sensors, old style chaincase being NLA

Hi iang6766, You are 100 % correct - and i should have know better than questioning your comments . I had just noted at some stage that numbers were different ... Yes I must have the later chain case (or the engine is later than the 2004 i had assumed) so yes do have the different size boss in the case... Good to know that sensors are same specs

I'm going to chuck this one amongst the workshop techs,in the mean time,if you go out again,try running the motor at the necessary rpm but at a different hull speed, so SB motor only as fast as necessary to get port rpm to 5300. I once had a through hull pick up causing just the right amount of water aeration round the water pick to cause an overheat, either side of that speed was fine. Weirder things can happen that one doesn't think of. I have never had a BF150 behave this way, usually the overheat occurs above a given rpm.So if it doesn't overheat at a lower boat speed you need to look at the hull to see what could be causing it.

Ok iang6766 that I can do. I will do the other tests with the laptop - hopefully tonight - if rain stays away then try some more on water testing at the weekend. Been preoccupied with these temp sensors and still need to do more to satisfy myself but you may be onto something...
Before I mentioned overheating on this forum, cavitation or lack of water being sucked in played on me. Being a CAT with fairly narrow hulls though it seemed like a lack of water issue initially. The anti cavitation fins do sit about an inch higher than the bottom of the hull... ( no pods ) cant really drop engines lower due to the exhaust idle ports being a bit closer to the water than I would deem safe . The bottom of this alloy hull did have some "V" type extensions that I though may have been interfering with waterflow so i lobbed them off. One thing I have also noticed is the engines are toeing out ( front of motors closer together than the rear ?? ) .. so somewhat of a rooster tail as close as 5 meters from the rear of the boat... so also wonder if this toe in... although not a ridiculous amount is affecting the water flow in at least one side of the intakes. One thing I always think about is how quickly my old yamahas ( different boat ) would alarm if something got stuck around the water intakes... Very quick to alarm even at slow speeds so seemed to me to be super sensitive to lack of water or heat.. Perhaps different story with these Hondas...

I will keep at it ... plenty to keep me out of trouble

One more thing to try, how about trying a clear pipe from the thermostat housing down to the plastic junction so you can watch what is happening at the exit from the thermostats, never done it but this is a one off problem that needs a little ingenuity .This has really got me head scratching.

Tried my fancy new knock-off Honda scan tool last night and seems i have damaged the little black box that comes with the loom. Will try to have fixed local but doubt it... I guess that was worth the AUD $300 for the 30 odd minutes use i got out of it..
Will try some more on water antics at various speeds this weekend and report back re possible hull / water intake issue

Cheers

Oh no!
I didn't know you were in Australia or I might have suggested the Dr. H tool by BRP DIAGNOSTICS. That software and interface is made in Australia and is Dr H "backward engineered" according to the owner of the company.
So sorry Shane!

Hi jgmo,
I'm actually working / living in Papua New Guinea. I'm a Kiwi but do get a lot of stuff over here ex Oz . The unt I got was from the states. Honda Marine Diagnostic software ( Marine HDS ) Got a local guys that's trying to repair now. Really am keen to ID the one temp sensor that is causing this issue.

So guys, The weather is still rubbish over here so hard to get out and get testing done. I did remove both thermostats from the engine this last weekend and gave it a short blast but the alarm/light came on at approx 4500 vrs the normal 5300 ish . Refitted T/Stas while on the water and alarm resumed its normal 5300 RPM issue. Also removed the 2 water intake screens ( these are new ) just to try - thinking may allow more inflow of water.. didn't make any difference.

Wow! 800 rpm difference is significant! But what does it mean? I sure don't know!
Hmm. My boss had the HDS and, as far as I know, it is still used by dealers. But we didn't have anything bigger than a 20hp in the rental fleet so I never got to use it.

I hope your guy there can get it sorted for you!

Good vibes is all I got at this point.

Hi jgmo and iang6766

Been out of country for last few weeks so no real new info besides little testing i did in shop yesterday that will hopefully get closer to the reason for the overheat alarm... so I will share with you as might shed some light...

So I did manage to have the Honda diagnostics box repaired and it is now working as before.

On the main screen it only shows 3 of the 4 temp sensors and when monitoring in the past ( and on the water ) none of these showed high temps.
So by unplugging each sensor all 4 set of the o/heat alarm so that's good...
On this HDS unit it gives a number to each temp sensor as follows -
sensor 1 ( block sensor - RH side of block )
sensor 2 ( thermostat housing - rear )
sensor 3 ( Top of exhaust manifold )
Sensor 4 ( thermostat housing - front )
Seeing as i didn't notice any high temps on the 3 sensors that display on the main screen before i'm guessing that it may be sonsor 4 that has the issue. When it ( # 4 ) is unplugged and alarm is sounding there is no indication of fault on the main screen but it does leave a "code" on the "fault list" screen. I have never noticed this while on the water but perhaps been paying too much attention to the other 3 sensors and been distracted as the "overheat" alarm does clear itself on the water very quickly...

So I bough back some resistors with me from my travels . I did some playing yesterday and found I can potentially trick the ECM into thinking its 44 deg C / 56 deg C or 79 deg C by using one of the 3 resistors in place of the variable temp sensor.

So I m guessing that if i fit the 300R resistor in the place of the sensor, telling the ecm we are at 79 degree's and have picked the correct troublesome sensor circuit , water test at 5300 should then stop the o/heat alarm coming on. This would then tell me the engine is in fact over heating ( even though i've used the temp gun on all surfaces ) or there is trouble in the wiring from sensor to ECM. As per previous rambling posts all 4 temp sensors and ECM's have been swapped with good engine ...and didn't fix the problem

Be happy to know your thoughts...

Cheers

Shane

Shane,i'm impressed by your reasoning, just one comment. The front thermostat should open at 60 deg C and that sensor should not show more that 65 deg max. The only one that should get up around 80 to 100deg is the block sensor, no.1.Are you certain you have a 50 deg thermostat closest to the cyl head and the 60 on the block side?

It sounds like you've thought it out pretty thoroughly except maybe what Ian has suggested. You could still use the 44° resistor to check the #4 stat circuit but following the temperature sequences that Ian points up is going to be important.

I have nothing to read on this so it's above my pay grade so to say. I am interested in the problem though and hoping for a positive outcome for your efforts.

Keep swingin' at it!

I was looking at the electrical drwg it seems that the buzzer and indicator light is already connected to the positive the 4 sensors seem to be the negative side of the indicator and buzzer if the thermal switch in the sensor comes into the normally closed position it will bridge and the negative circuit will be completed and trigger the alarm and indicator light on, now you don't know which sensor is causing the trouble out of the 4 what i will do is connect a globe to each sensor and the globe that comes on will point out which sensor is the problem connect 4 globes if none of them come on then start looking elsewhere

Tegwini has a good idea but if the 12v supply is from the ECM or a solid state module you won't want to use incandescent bulbs if you do this. Even a low Watt tungsten filament bulb has a high ramp current that solid state circuits don't handle very well.
You don't want to let the smoke out.

Hi jgmo, there will not be any smoke the ECT sensor is a RTD as the temp increases so does the resistance when the resistance increases it produces between 4.30v and 5.25 volts then connect a globe between the r/w and g/r wires the g/r is earth if the globe comes on when the temp picks up the sensor is working.

Well, I've never heard of a temp sensor "producing" volts so I guess I'm not understanding your point.

At any rate, my precaution still stands that incandent bulbs should not be introduced into any solid state circuit without using due care. A well trained electronics person could devise a way to do it but most of us don't have that in depth knowledge.

That's all that I was trying to point out.

It wouldn't hurt, all you're doing is using a globe to see if the sensor is going to ground prematurely.

2 strokes use thermal sensors and 4 stroke use RTD,s its,s also called Pt 100

Correct, so when a 4 stroke sensor shows o/heat, resistance goes to zero, ie ground, this voltage reading to ecm increases towards 5v

And by using the globe method we can determine which sensors are working and which one is triggering off the alarm and indicator lights.