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  1. #1

    Default Honda BF 150 Overheat Alarm

    Serial # BANJ 1200500

    This is a new one for me. It has been difficult to diagnose this issue.

    Started a month or so ago with the starboard motor. ONLY when accelerating out of the hole will I get an alarm. If I very slowly bring the boat up to speed there is a chance that it wont come on...

    I checked the paperwork I recieved when I bought the boat three years ago. 2006 KeyWest 268 with a pair of BF150's. Sold new in 2008. It had 280 hours on it and the seller produced a bill from his marina where the 300 hour service was done. New impellers as well as thermostats and the rest of the normal maintenance items.

    The rig now has 550 hours and when this started I pulled the LU's and put in new impellers. I did leave the metal housings. Buttoned everything up and damned if the same thing happened.

    Once on plane and at any speed, it runs great. Good pee stream and no alarms once underway.

    Only when accelerating. Any ideas?

    I'm considering poppet/bypass valve...but wouldn't that be a constant problem. Especially at speed?

    Thanks!

  2. #2
    Join Date
    Apr 2016
    Location
    barnegat NJ
    Posts
    2,706

    Default Re: Honda BF 150 Overheat Alarm

    Poppet valves come into play usually at higher rpms, Wait for other replies. Always replace entire pump and seal them.

  3. #3
    Join Date
    Mar 2009
    Location
    Cincinnati, OH USA
    Posts
    4,176

    Default Re: Honda BF 150 Overheat Alarm

    When you get an alarm, what is the status of your warning lights? Check engine light on? Oil light on? Overheat light on? Battery light on?

    You may not have noticed....but that will provide much better direction to solve the problem.

    Mike

  4. #4

    Default Re: Honda BF 150 Overheat Alarm

    The overheat alarm is the only alarm that comes on. Red light and solid warning tone, along with reduced RPM...

    I turn the motor off and almost immediately restart it. And many times the second time I power up on plane I dont get the alarm.

    I usually run out one channel where I have to idle for twenty minutes or so. Then I power up and get on plane..

  5. #5

    Default Re: Honda BF 150 Overheat Alarm

    Is it possible that a bad sensor is involved?

    I was thinking not, as the problem goes away and an intermittent sensor should keep giving me alarms, not just under power-up

  6. #6
    Join Date
    Apr 2016
    Location
    barnegat NJ
    Posts
    2,706

    Default Re: Honda BF 150 Overheat Alarm

    sensors can be tested with an ohm meter, trace sensor wires,look for a worn wire,bad harness connections around a moving linkage,throttle

  7. #7

    Default Re: Honda BF 150 Overheat Alarm

    did you rectify your problem?

  8. #8
    Join Date
    Jun 2008
    Location
    Posts
    555

    Default Re: Honda BF 150 Overheat Alarm

    Had a similar issue on a Bf175. Removed some debris from the poppet valve and that seemed to fix it.

  9. #9

    Default Re: Honda BF 150 Overheat Alarm

    I have not torn into it again, nor have I had the boat back out on the water.

    If the sensor had a bad wire or was intermittent, I would get an alarm at any time.

    The ONLY time I get an alarm is when accelerating and jumping up on plane. This is why I am having a hard time finding the culprit. If it would happen at any other time I could plug a bunch of new variables into the equation....

    I have plans to pull the poppet valve so will be looking in that direction...

  10. #10
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
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    3,725

    Default Re: Honda BF 150 Overheat Alarm

    When you replaced the old impellers, were any of the vanes missing? One possibility is that you have a partial blockage in one of your cooling passages. The shortcut fix for that is to drop the lower unit, remove one T-stat at a time, and stick a garden hose in there, seal with a tape or rag, and put as much pressure as you can get and try to flush it out.

    I guess on other obvious thing is whether you checked the intake screens on the lower unit for blockages or debris. The screens need to be removed completely to check them. Easy to do.
    CHawk 25 DLX

  11. #11

    Default Re: Honda BF 150 Overheat Alarm

    Quote Originally Posted by chawk_man View Post
    When you replaced the old impellers, were any of the vanes missing? One possibility is that you have a partial blockage in one of your cooling passages. The shortcut fix for that is to drop the lower unit, remove one T-stat at a time, and stick a garden hose in there, seal with a tape or rag, and put as much pressure as you can get and try to flush it out.

    I guess on other obvious thing is whether you checked the intake screens on the lower unit for blockages or debris. The screens need to be removed completely to check them. Easy to do.
    The old impellers were like new, with only 250 hours on them. No missing vanes.

    I have removed the screens and used pressure to flush anything that might be in there..

    What I have a hard time understanding is if it were a blockage, wouldn't that have an affect while running at speed?

    This overheat alarm will only come on when I am accelerating.

    Thanks for your post

  12. #12
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
    Posts
    3,725

    Default Re: Honda BF 150 Overheat Alarm

    The faster the engine rotates, the more water is pumped through it. As you start to accelerate, a takes a bit of time for that additional water to get through the block and heads and out the exhaust tubes, so it could possibly be that margin of difference due to some restriction in the water passages that is setting off the alarm. That's just speculation.

    Have you pulled the heat sensors and tested them? I don't know the specs on the 150, but on the 225 at ambient temperature, around 70 F, the resistance should be about 5000 ohms. At 160 F the resistance should drop to about 500 ohms. Yours should be similar. The resistance curve is nearly linear.
    CHawk 25 DLX

  13. #13

    Default Re: Honda BF 150 Overheat Alarm

    Quote Originally Posted by chawk_man View Post
    The faster the engine rotates, the more water is pumped through it. As you start to accelerate, a takes a bit of time for that additional water to get through the block and heads and out the exhaust tubes, so it could possibly be that margin of difference due to some restriction in the water passages that is setting off the alarm. That's just speculation.

    Have you pulled the heat sensors and tested them? I don't know the specs on the 150, but on the 225 at ambient temperature, around 70 F, the resistance should be about 5000 ohms. At 160 F the resistance should drop to about 500 ohms. Yours should be similar. The resistance curve is nearly linear.
    Thank you for your post....

    I have been pretty busy as late and have yet to get back on this issue.

    I will post up my findings when I get this corrected

    Thanks to all for your help...

  14. #14

    Default Re: Honda BF 150 Overheat Alarm

    Step one: Check the temperature with a infrared thermometer to verify you are overheating.

  15. #15
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
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    3,725

    Default Re: Honda BF 150 Overheat Alarm

    Also, when this happens again check that your green oil pressure light remains on. If not, you may be barking up the wrong tree. There are only two things that will cause the engine to drop to 1800 rpm - overheat and low oil pressure. If the overheat does not resolve itself within 20 seconds at the 1800 rpm's, the engine shuts down. If the low oil pressure does not resolve itself within 20 seconds, the engine will continue running at 1800 rpm. At least that's what the manual for the BF 225 says. I suspect the 150 is very similar.
    CHawk 25 DLX

  16. #16

    Default Re: Honda BF 150 Overheat Alarm

    Thought that I would report back on this problem...

    Both of the thermostats as well as the pressure relief valve was replaced and I no longer have the overheat issue...

    The relief valve was in very good condition. Both of the thermostats were corroded, even though they only had 280 hrs and were flushed every trip..

  17. #17
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
    Posts
    3,725

    Default Re: Honda BF 150 Overheat Alarm

    Well, there is mounting evidence that fresh water flushing of the bigger Honda's doesn't do a lot of good when it comes to thermostats. Apparently, the flush water doesn't get high enough into the manifolds to get to the thermostats unless there is extraordinary water pressure from the flushing hose. Next time I pull maintenance on my 225, I plan to pull the t-stats and see how much pressure it takes on the flush hose to get to them. Will let folks know.
    CHawk 25 DLX

  18. #18

    Default Re: Honda BF 150 Overheat Alarm

    One thing not to be overlooked the higher the rpm the greater the water pressure with a slight leak in the cylinder head gasket will set the alarm off creates super heated steam in the exhaust area this will only happen as the rpm increases .read the manual .

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