Logo

Honda BF75D 2007 overheating at high rpm

Ruigie

Member
Hi all,

I recently purchaseda 2010 Beneteau Antares 580 with a 2007 Honda BF75D outboard.
Mecanic changes impeller and oil before going out the firsttime.
After an hour an intermitent alarm went off and after thatthe engine stalled.
Engine started without problem and we returned at 3500 rpmwithout problem.
Resulted to be water in the gas, so we changed all the gas,filters and cleaned both separators.
Got on the water again, trolling a few days without problemsand returning at 3500 rpm.
Tried WOT for a change and after a minute the engine stalledand the temperature light and alarm got on.
The engine started without any alarm after that, got back tobase and called the mecanic.
As he was to cometake a look I told him to take a look at the fresh wáter intake also because itseemed to be stuck.
He changed the thermostat as it was rusty and dirty and withsome salt on it, but he didn´t look at the intake.
Tried again and had the same problem.
Got the boat out of the water and the mecanic had a look atit again, taking the leg of.
Said the tube at the entrance of the cooling circuit haddirt in it, that might be the cause.
Also the fresh water intake valve was stuck due to salt slagand dirt.
Put the hose on it, water came out without problem (one ortwo pieces of sand)and the water from the pee hole came out strong.
Got out again and after a while had the same problem.
Now I told him to replace the temperature sensor….
Anyone any ideas ?
Thanks
 
Your mechanic should have already done a reverse flush of the system through the thermostat housings. Anytime an outboard seems like it's overheating and the gear box is off is a good time to remove the thermostats and use a professional power flush tool to seal in the water and shop air pressure to force flush the internal passageways so that any trapped debris can exit the bottom of the engine block via the water tube connection. This is also the appropriate time to replace the TWO thermostats, one at the head and one in the block, as well as the water tube seals.

The longer it takes to solve an overheat issue and you are still pushing the boat, the more it's going to overtemp, go into power reduction and frustrate you and your crew.
Not to mention the damage that could be occurring to your outboard. While the built in power derate engine protection works very well at minimizing engine damage, it is not designed to be a 100% guarantee against hurting the outboard.

Have you verified that it is actually overheating? Replacement of the sender isn't a bad idea but if that doesn't solve your problem then the next move should be to monitor engine temperatures while the fault is occurring. After BOTH tstats are replaced. A quality, infrared, no touch, heat gun can reveal good information upon which to act.

One other thing that gets neglected when an older, fuel injected engine tends to overheat while being worked hard is a lean fuel condition. If you do all that's required of cleaning and maintenance to the cooling system but the problem persists, then you may need to investigate the fuel delivery. This can be as simple as cleaning the VST and replacing the filters to pulling the injectors and cleaning and checking them for proper flow and spray pattern.

While I realize some of the procedures I've laid out aren't always readily available at dockside or even a marina, I wanted to point out what, sometimes, just has to be dealt with.

Here's hoping that you can get it sorted out and then simply enjoy the water.
 


Many thanks for your reply !


My mechanic has a Suzuki outboard shop but obviously doesn’twork a lot with Honda outboards as he insisted that this engine has only onethermostat.I finally convinced him there are two sending him some pictures…


I’m going to try the engine dismounting the thermostat thathasn’t been changed to see if it fails again.


If it does I willcall the Honda repair shop to see if they can finally solve the problems.


Meanwhile theseason is ending fast.


The mechanic didn’t do as you suggest when the gearbox wasoff due to lack of tools I guess, but if I have to take the boat out of thewater again we will do so.


He « fixed » the flush valve that was stuck due tosalt, I put the hose on it and left it running for over han hour.


After the first try-out giving the same overheating alarm Iwent back to my berth and put the hose on it again.


Now when I start the engine water comes out of the flushingvalve so the valve obviously doesn’t close now…


I tried various things but it still doesn’t close.


The boat has a year of garantee but it is rather expensiveto hire a trailer and trail it up and down to the (professional)seller , not tomention two working days.
 
Yeah, I have had trouble with Honda flush valves not seating and leaking after being used. But, they are simple devices that most can open up and repair. If the engine is mineraled (salted) up, they usually just needs a good cleaning inside.

Salt encrusted engines can also be very difficult to get flushed. The minerals tend to become embedded in the metal and can affect heat transfer. There's no sure fire method for cleaning but I have had some degree of luck using vinegar in a trashcan and then rinsing but this doesn't work on heavy encrustation. The only real fix is to practice prevention by flushing after use.

There are threads on this forum about vinegar and using Salt Away with advocates and detractors of each.

While you're doing work on the thermostats, you can check and replace internal zincs and use small stainless steel brushes to gently remove loose material inside the housings. If the housing is bolted on, you can also take it off and do some "deep cleaning". This makes back flushing easier and more effective too. Just keep in mind that you don't want to remove the cast aluminum trying too hard to scrub, scrape salt. You can only do so much this way.

It may actually be worth the time, hassle and expense to take advantage of the guarantee you have if you're not willing or able to do this work yourself. Just make sure you ask about the work being done and, if at all possible, get a sea trial before taking the boat home. Document everything in the event this just can't be repaired. That will help you if you need to pursue this with the dealer.

I hope that you get it sorted out.
 
We took out the cilinderblock thermostat and both the tip as the spring were completely covert with salt slag.
Also a lot was to be seen inside the housing.
We put the cover back on with the thermostat out and put the hose on the flushing.
The water came weakly out the pee hole but a lot out of by the propeller.
I hope this is normal?
 
Also we cleaned both thermostat housing on the inside the best we could.
While cleaning as deep as possible on the inside with a iron wire with the tip doubled in order not to scratch the surface, my friend tells me the wire came out with the tip straight.
now he doesn’t know if the doubled tip broke off inside or just straightened up....
Were would the lost piece go if the engine started and where if we put the hose back on the flushing mount?
 
I am going to let the Suzuki mechanic replace the thermostat ans flush valve but if the problem isn’t solved,i’ll take the boat back to the dealer that sold it...
 
Well, it does sound like you may have found the problem. My guess is that the wire just got snagged and was straightened out. If you closely inspect the tip it should be obvious if it was cut or fractured and broke off. Either way there's not alot you can do about it now. If you determine that it broke, you may be able to retrieve the piece by attaching a powerful magnet to the wire and push it back in there and see if the piece can be attracted and pulled out. Otherwise it will probably rust and dissolve eventually. Likely not a big worry.

Your question about how the flush water comes out pee hole a little and most out the extension sounds normal to me.

I hope this work solves your problem. I think that it might.

Good luck.
 
Yesterday the second thermostat was replaced, so today I went out to try.
got out on open sea and kept the revs high for a few miles without a problem.
got back into the bay and hit WOT and no problem neither.
On the way back hit WOT again for about half a mile and lifted the trim a bit .....and the alarm went off again!
This time I could see quit some vapor coming out.
Stopped the engine and started again without a problem , neither vapor nor alarm.
Guess it’s time to take it back to the dealer��
 
So, do you think replacing that thermostat made ANY improvement?
If so....you're headed in the right direction. If not, I'm not sure what that might indicate. I'll have to think about it some more.

At any rate, I think taking it in to the dealer would be wise. You don't want to wait until your warranty is expired.
 
Today we went for a trip with the family, and even at wot no overheating signs.
For this boat and about 320 kgs of people on board an 75 hp outboard is obviously underpowered, but the engine didn’t heat up as it did before.
Even after half an hour at high revs.
the alarm it gave this morning was only after trimming the engine a little bit up .....the boat gained speed but after a while the alarm set off, maybe at this position the water intake picks up too much air.
We are going to change the relief valve and the temp sensors.
On monday i’m talking to the sellers and see what they say.
thanks again for your advice!
 
Well, the situation does seem to have improved.

But now I wonder why you experience issues when you trim. That makes me curious about how your motor is mounted. Where is the cavitation plate in relation to the bottom of the hull when the plate is horizontal?

Theoretically the cav plate and hull bottom centerline should be at about the same height. Having the plate 1 to 2 inches lower works for many installations but higher is not typically recommended unless some sort of transom extension is being used.

You may want to measure this and discuss it with the dealer when you call.

Good luck.
 
Finally got out to do the trial, out at sea at WOT got to 20 knots, but when geting off the throttle the alarm went of.
turned the engine off and after half a minute on again and no alarm.
returned to the bay to try there, at WOT 24 knots but after a minute the alarm went of again.
Back at the berth I took off the hood and the engine was very hot.
Took out one of the thermostats ( the easy one) ,it was wide open with some sand and salt in it.
Put the hose on and after a minute the engine cooled off considerably.
Looking at the pics my fear is now that along the cooling circuit where we have no access another clog of salt obstructs enough flow of cooling water at higher rpms....
When on the shore I flushed the engine with vinagre and water intermittently during one and a half hour but as the pictures show not to much effect.
after replacing the anodes and cleaning all visible parts the mechanic had Salt Away solution running through it for some time.
any ideas?
 
Finally got out to do the trial, out at sea at WOT got to 20 knots, but when geting off the throttle the alarm went of.
turned the engine off and after half a minute on again and no alarm.
returned to the bay to try there, at WOT 24 knots but after a minute the alarm went of again.
Back at the berth I took off the hood and the engine was very hot.
Took out one of the thermostats ( the easy one) ,it was wide open with some sand and salt in it.
Put the hose on and after a minute the engine cooled off considerably.
Looking at the pics my fear is now that along the cooling circuit where we have no access another clog of salt obstructs enough flow of cooling water at higher rpms....
When on the shore I flushed the engine with vinagre and water intermittently during one and a half hour but as the pictures show not to much effect.
after replacing the anodes and cleaning all visible parts the mechanic had Salt Away solution running through it for some time.
any ideas?
Important to mention, besides oils, filters impeller and pressure valve were changed and no visible debris visible from lower end up.
 
I've never tried doing it but have often thought of using CLR, full strength, to try to clean deposits out of an outboard.

The reason I have been considering this is that where I live, the well water is VERY hard and mineral deposits in appliances and plumbing fixtures is a regular problem that I've learned that CLR works really well for.

So, I have been thinking that salt is just another mineral that might be dealt with using this very effective product.

The scary part is that I've also learned that salt tends to not only "plate out" on aluminum but actually seems to structurally bond with that metal. When scraping and wire brushing engines with a lot of salt buildup, you have to be careful not to be too aggressive with removal so that you aren't removing the metal as well.

So, I CAUTION you that this is just an idea and I have NEVER actually tried it.

Any CHEMISTS out there?

Good luck.
 
To afraid to use CLR, used pure vinagre through the stats housings and let it sit overnight before rinsing with fresh water.
after starting overheating alarm went off but stopped after 10 seconds (didn’t have time to even heat up!).
went yesterday for a run at WOT inside the bay, achieved 24 knots at 4800 rpm with 13 1/4 x 17 prop before going into limp mode with alarm again.
Used a heatgun to check and block was at 149 degrees F, head about 130.
can this mean it is not actually overheating?
Also shouldn’t the rpms be in the 5500 range rather than 4800?
And last, I called the Honda workshop to have them put the computer on it to see what it reads, first thing he said was that this engine doesn’t have this option?
 
Ruigie, Dr H can communicate with your motor, however, it only logs the number of overheats it has experienced. From my experience , I have had a number of these engines with this same issue , quickest and best way to fix is to remove the cylinder head and clean out the block. Every one I have done has had salt and silt packed around the bottom cylinder, there is no chemical I know of that will fix this.
 
Ruigie, Dr H can communicate with your motor, however, it only logs the number of overheats it has experienced. From my experience , I have had a number of these engines with this same issue , quickest and best way to fix is to remove the cylinder head and clean out the block. Every one I have done has had salt and silt packed around the bottom cylinder, there is no chemical I know of that will fix this.
OK, will first wait what the Honda mechanic can tell me but sure will see to have the head lifted to see how the circuit is.
What temperature should head and block give by heatgun after running at WOT?
Thanks for your advices guys!
 
You cannot accurately measure with a heat gun, use Dr H, block temp should not exceed 100 deg C, it will take about 15min of hard running to get there
 
Stillbwaiting for the Honda workshop guy to get back to tell me when he will have time to take a look, probably not in August...
Anyhow the other issue I had was the boat not getting on plane easily and when it did on flat water with the actual 13,25 x 17 prop, it didńt get past 4800 rpm.
I have ordered a 13,75 x 13 prop to see if this helps and we’ll see if the alarm goes off again.
Want to have the head pulled to see how the passages around the cilinders are...
 
Stillbwaiting for the Honda workshop guy to get back to tell me when he will have time to take a look, probably not in August...
Anyhow the other issue I had was the boat not getting on plane easily and when it did on flat water with the actual 13,25 x 17 prop, it didńt get past 4800 rpm.
I have ordered a 13,75 x 13 prop to see if this helps and we’ll see if the alarm goes off again.
Want to have the head pulled to see how the passages around the cilinders are...
No news from the Honda shop yet, but now sometimes the alarm goes off after 5 minutes at idlle at the berth...desperate, going on holiday but hope to have news from the workshop soon...
 
Got the boat finally back.overheating issues solved after a circuit cleaning with some sort of acid dilluded with water (which damaged the ˋpaint a bit).
no more overheating issues anymore even running at 6000 rpm for a while.
holeshot improved with 13 prop , rpms at wot go well over 6000 rpm.
still waiting good w4ather for further tests.
 
However, if you need more information in this chemistry domain, you can access a student help source for chemistry help. I chose this subject of salted engine oil process and consequences, and I found on https://essays.edubirdie.com/chemistry-help great expert writers who provided me with reliable data. I understood perfectly how ordinary salt (a highly charged compound) quickly dissolves in water; however, it is insoluble in oil, gasoline, or alcohol. Then it will remain in solid form and will never make it past the fuel filter to the engine. So, the writing service is useful for learners who have trouble with homework, need chemistry help on dissertations, and also for usual users of cars since chemistry is the base of any process.
 
Last edited:
Most common issue, passages blocked behind the block thermostat. Best to remove electrical box to gain proper access to inspect/ clean.
 
Back
Top