Honda BF90 temperature indicator / buzzer

Can anyone please help me to solve my problem with my Honda BF90 encounter today?
Here is the sequence of events:
1. Just after casting off with engine running at approximately 2000rpm the overheat light and buzzer came on and rpm dropped.
2. Checked and confirmed that water is flowing from the water signal outlet.
3. Switched off engine and restarted after about 2 minutes.
4. Same thing happened as above.
5. Switched off engine and restarted after about 2 minutes.
6. Engine running OK at 2000rpm for about 5 minutes.
7. Increased rpm to 3000 and again after approx. 2 minutes the overheat light and buzzer came on and rpm dropped.
8. From the boat out at sea I phoned a friend and after explaining what happened he said that the thermostat might have got stuck closed so I opened the plastic thermostat cover, removed the thermostat and closed the cover.
9. Restarted the engine and since I was a bit convinced that the problem was the thermostat I ran the engine on 4000rpm.
10. Just after a couple of minutes same thing happened.
11. Switched off engine and headed for shore with my auxiliary engine.
12. Got the boat to the garage and as usual with engine running at idle ran fresh water through the engine to rinse it.
13. I never use the flush port to rinse the engine but I feed fresh water from the normal intakes near the propeller using ‘headphones’.
14. Switched off engine and opened the thermostat cover.
15. With fresh water running I switched on engine and just after a few seconds water was flowing from the thermostat port.
16. Switches off engine and am asking for some guidance.

Since you said you opened the plastic cover, I am assuming you have a 90 hp fuel injected.

If you do...there are two thermostats. One in the block and one in the head. You probably removed the one in the head, since it is easy to see. The one in the block is just to the right of the one in the head. It is behind the ECM. The black plastic housing around the ECM has a hole in it, so you can get to it.

You may still have a bad impeller, bypass valve or temp sensor...but I would check the second thermostat first. It is a different temperature than the head thermostat, so do not get them mixed up.

Mike

Thanks a lot for your help. Yes it is fuel injected. I will check the second thermostat during this weekend and if you do not mind I will comunicate to you the findings.
Cheers

Hi Mike,
Forgot to mention that the boat had been in the garage for about 9 months due to an accident with my back however as always I had flushed it with fresh water and salt away solution.
Here is what I did after your recomendations
1. Located the thermostat in the block and removed the cover. Tried to extract the thermostat but it was stuck in its cavity. Tried several times to remove it by inserting two screw drivers underneath the round metal part that forms part of the thermostat assy and levered it. This sub-assy (round metal part and spring) did give and I managed to work it mechanically but still did not manage to make it get dislodge from the cylinder block cavity. I used moderate force because I was afraid that if I use high force I would deform the spring assembly, it gets loose and spring would fall inside the block.
2. Tried also carefully lever the thermostat from the seal that houses the thermostat with a screwdriver but still in vain. Sprayed penetrating oil but still for nothing.
3. When I ran out of ideas I held the thermostat open and pumped some ‘Salt away ‘ solution from it to remove any possible blockage of salt in the passage way.
4. Fixed back the thermostat cover and went to try the engine out at sea.
5. Again after approx 3 minutes engine running at 2000rpm the buzzer and warning light went on.
6. Removed the cylinder head thermostat and tried again. Engine was running fine at 2000rpm. Increased to 3000rpm and engine was fine for a whole 30 minutes. At that point I thought the problem was solved and it was due to a bad cylinder head thermostat and a stuck cylinder block thermostat which got loose after my trying to remove it.
7. Wanted to make sure the problem was resolved so I Increase to 5000rpm but for only a minute because of the sea condition.
8. Reduced to 4000rpm and everything was fine for a whole 15 minutes when again the buzzer and warning light went on.
9. Very disappointed headed for shore and went to find some information to locate the bypass valve and temp sensor that you mentioned earlier. I did not manage to find the by-pass valve and there are more than one temp. sensor in the illustration. Maybe the by-pass valve is shown under a different name. Below is the link to my engine illustrations: http://www.boats.net/parts/search/Honda/Outboard%20Engine/2007%20and%20Later/BF90DK0%20LRTA%20/parts.html If you find some time I would appreciate very much if you have a look at it.
10. Today I am off to buy following:
a. both thermostats
b. O- ring for both thermostat covers
c. Water jacket cover gasket
d. Impeller kit
Any feedback from your side is very much appreciated.

The relief valve is # 6 http://www.boats.net/parts/search/Honda/Outboard%20Engine/2007%20and%20Later/BF90DK0%20LRTA%20/MOUNT%20CASE/parts.html

It might be stuck open or it might be stuck closed.

I have a feeling there is a partial blockage somewhere. When you get the block thermostat out, it will give you a better picture. It does sound like you are headed in the right direction.

Since things have improved...the temp sensors are most likely not your problem. Although, they could be reading incorrectly due to salt deposits on them. Since you are doing all this, you might pull the sensors (that you can get to) and check/clean them.

Make sure you put the right thermostat in the right place...they are different temperatures.

I do not have to deal with salt, here in the midwest (thank goodness!). Maybe someone else on the forum or your dealer can give you some suggestions for cleaning those passages out.

Mike

Just to inform anyone who might encounter same problem here is how I managed to fix my problem.
I managed to dissolve the salt that was jamming the cylinder block thermostat by pouring some white vinegar around the periphery of the thermostat seal and repeated this procedure for three times leaving a 15min interval.
When I managed to remove it the lower part of the thermostat was full of dry salt and I thought no wonder my engine was heating up. However when I investigate further and looked at the thermostat cavity in the cylinder block to my surprise I found a wall of dry salt blocking the passage.
I carefully removed / scarped the salt with a screw driver and managed to clear the passageway. With a pipe and by siphon I passed 5 Liters of water through this passage.
Fixed the thermostat cover but without the thermostat, removed also the cylinder head thermostat and ran the engine with plenty of tap water that was around 23 deg. Centigrade. Left the engine running for about 15 min.
Fixed back both thermostat (replaced with new ones) and this weekend went to try it out. Engine was behaving as if it was new and since weather was permitting I even ran it for some time at 5100 rpm without any problems.
Thanks to Mike for guiding me and gave me directions as where to look to try and solve my problem.

Thanks for the feedback as to how to solve the problem once you found it. Those of us in fresh water areas do not have these issues, but it is nice to have a solution in case someone comes in that ran their motor in salt water.

Mike

Excellent post guys. Will be helpful for many others.

hondadude said:

Since you said you opened the plastic cover, I am assuming you have a 90 hp fuel injected.

If you do...there are two thermostats. One in the block and one in the head. You probably removed the one in the head, since it is easy to see. The one in the block is just to the right of the one in the head. It is behind the ECM. The black plastic housing around the ECM has a hole in it, so you can get to it.

You may still have a bad impeller, bypass valve or temp sensor...but I would check the second thermostat first. It is a different temperature than the head thermostat, so do not get them mixed up.

Mike

Click to expand...

Hi, I know I'm digging up an old thread but I'm having the same problem. Do you know where I could see some photos of the thermostat location for both the fuel injected and carbureted Honda 90? Thanks for any help!

I have the same issue with my 1997 BF75A.

It ran fine for a couple of hours and then I got the intermittent beep and the RPM dropped.
The flow indicator was working fine.
The engine was not particularly hot to the touch.

I replaced the thermostat (I believe there is only one on this carbureted model) but still getting the alarm.

Any help would be GREATLY appreciated.

Thanks, Hal