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  1. #1

    Default BF225 overheating at idle but not at higher revs...

    Took the boat out today for the first time since the virus lockdown opened up. Over winter Iíve replaced plugs, low pressure fuel filter and external fuel filter, drained VST but not changed HP filter, fitted new impeller and housing and had lower unit rebuilt and pressure tested at a local shop.

    i havenít changed T Stats. Water is coming out through telltale.

    We went on a good run - 8miles offshore, fished the drift many times then thought Iíd open her up to WOT for about 5 mins on our way back in. All fine no issues. Then we slowed down to idle to setup to drift local reefs and the overheat sensor went off (red light on throttle housing and continuous alarm). I switched of engine and check water inlet filters on outside of leg - both sides clear. Restarted engine and ran her at higher revs for a bit to get closer home - again no problem. Slowed down to hand line for mackerel and again at low Revs the overheat alarm went off. Switched engine off and Had a bite to eat before heading in as didnít want to risk damage. Again as Iím trying to manoeuvre boat in the harbour the alarm went off.

    The thing I donít understand is the overheat alarm is only going off at idle not when Iím pushing faster - could this be caused by faulty T stats or something else? Help appreciated.

  2. #2
    Join Date
    Sep 2008
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    Hague, Virginia, USA
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    Default Re: BF225 overheating at idle but not at higher revs...

    Could be faulty t-stats - one not fully opening, or coated in gunk. Remove t-stats, put in pan with water covering, heat up the pan of water, use cooking thermometer, and observe. (Don't let the thermometer sensor tip touch the metal in the pan.) They should begin to open at 140F and be completely open at 160F. Full open is only 3 mm.

    When you remove the t-stats look for any corrosion or debris in the t-stat seating area. Make sure that the water hoses are not kinked or compressed.

    Remove the intake screens on the lower leg and make sure gunk hasn't gotten in there and clogged up the intake passage.

    Are you getting any bubbles out of the telltale?

    Are you sure that you installed the impeller correctly?
    CHawk 25 DLX

  3. #3

    Default Re: BF225 overheating at idle but not at higher revs...

    Thanks Chawk - I’ll do as you suggest. I hope the impeller was done properly - it was done by the shop when they replaced seals and pressure tested the leg!

  4. #4
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    Default Re: BF225 overheating at idle but not at higher revs...

    OK. Let's assume they did it correctly unless all else fails to uncover the issue.
    CHawk 25 DLX

  5. #5
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    Apr 2018
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    Default Re: BF225 overheating at idle but not at higher revs...

    What's the age of the motor? Could be a bad grommet or corroded housing where the water tube from the water pump goes into the sump, leakage could result in insufficient water pressure at idle but okay once revs are increased

  6. #6

    Default Re: BF225 overheating at idle but not at higher revs...

    It’s a 2002 motor and what you’re suggesting is just what I was puzzling over - ok at high revs (pump overcoming some weakness in system) but suffering at low. I’ll change thermostats to start with and then check inlets and finally have leg off again s as me check water tube grommet.

  7. #7

    Default Re: BF225 overheating at idle but not at higher revs...

    Had similar issue and ended up have hole in the engine block from corrosion. Would be fine at higher RPM but low RPM was losing water pressure and getting hot. Hopefully this is not your problem, but could be a possibility.

  8. #8

    Default Re: BF225 overheating at idle but not at higher revs...

    Quote Originally Posted by clkelley78 View Post
    Had similar issue and ended up have hole in the engine block from corrosion. Would be fine at higher RPM but low RPM was losing water pressure and getting hot. Hopefully this is not your problem, but could be a possibility.
    Yes I hope it’s not that. How did you identify the cause?

  9. #9

    Default Re: BF225 overheating at idle but not at higher revs...

    I noticed a bunch of water coming out from the btm of the back lower cowling. I pulled the panels off and could see the water coming out of the block. Also noticed salt crystals under main cowling from the spray. The higher RPM the more it would spray. Hopefully this is not your problem. A few fixes you can do but itís cancer, once it starts rotting, itíll just find another weaker area in the block. I repowered. Motor had 330 hrs but was 2008 model.

  10. #10

    Default Re: BF225 overheating at idle but not at higher revs...

    Ok so I replaced both T stats and O rings today and checked that the waterseives on the bottom of the leg were all clear. Apart from a degree of corrosion on the port T stat everything seemed ok. But problem reappeared again when I ran engine at idle with continuous alarm. I have water coming out of pisser as a steady stream - not particularly fast but also I cant see any air in the stream either.

    given the symptoms I think I may drop leg off now and replace the rubber grommets on the water tube. Does that make sense to you guys?

  11. #11

    Default Re: BF225 overheating at idle but not at higher revs...

    A further update: I took leg off and inspected pump which looked ok to me. Then I pushed a hose up the water tube and by looking up inside mid section I could see water pouring out the end of the tube up where the grommet should be, I assume, sealing it in. Water was gushing out around that area. So my assumption is I have a disintegrated grommet or grommet housing starts end of water tube. I spoke to local shop who told me it could also be a stick open PRV - but given amount of water I thought I could see gushing from end region of water tube I hope it’s the grommet. Does what I’m saying make sense to you guys?

  12. #12

    Default Re: BF225 overheating at idle but not at higher revs...

    One other test I did before dropping the leg, was to remove hoses from Thermostats and run engine at idle. No water came out of t stat housings and finally the overheat warning came on. I throttled up in neutral and water came out of the t- stats - I guess the t stats didn’t have enough hot water pushing against them due to low water pressure in order to open up. It all looks like the leaking water tube is the problem unfortunately. I will try to remove old grommet and replace without taking mid section off if that’s possible using a long reach socket driver. Otherwise the mid section will have to come off. Is this a job for an amateur or should I get a shop to do it?

  13. #13
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    Default Re: BF225 overheating at idle but not at higher revs...

    You will have to remove the midsection so you can clean out the corrosion properly, you will more than likely need a new oil pan anyway

  14. #14

    Default Re: BF225 overheating at idle but not at higher revs...

    Ok so I know definitely that the problem is caused by a corroded flange and grommet at the oil pan end of the water tube. Iím toying with the idea of a epoxy putty repair vs new oil pan...
    Click image for larger version. 

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    you can see the flange has all but disappeared so the grommet is free to move around at the end of the water tube.
    Last edited by James t; 06-07-2020 at 06:07 AM.

  15. #15
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    Default Re: BF225 overheating at idle but not at higher revs...

    Given the vibrations that cruise through these engines as well as my own mindset, I don't think epoxy will hold up well. Fix it right and you don't need to worry about it again. I would replace with new parts.
    CHawk 25 DLX

  16. #16

    Default Re: BF225 overheating at idle but not at higher revs...

    Quote Originally Posted by chawk_man View Post
    Given the vibrations that cruise through these engines as well as my own mindset, I don't think epoxy will hold up well. Fix it right and you don't need to worry about it again. I would replace with new parts.
    I completely agree - that’s what I’ll do. I drained and removed oil pan to make sure there was nothing else seized or damaged ready for a new one. I think that and a couple of new exhaust gaskets should do it.

  17. #17

    Default Re: BF225 overheating at idle but not at higher revs...

    Do you use any sealant when replacing oil pan or just a bit of grease on mating surfaces and gasket?

  18. #18
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    Default Re: BF225 overheating at idle but not at higher revs...

    The shop manual doesn't indicate that you need a sealant. It does say to grease the water tube grommet before re-installing.

    Page 13-4 in the helm shop manual walks you through the process. If you don't havge the Helm shop manual, here is a link to the manual on line. You can save it to your computer. It's about 22 MBytes.

    http://planbmarine.com/wp-content/up...BF200A-BF2.pdf
    CHawk 25 DLX

  19. #19
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    Default Re: BF225 overheating at idle but not at higher revs...

    You must use a good quality sealant round the exhaust section of the gasket as per factory shop manual, this prevents corrosion, you will see it on the old one when you remove it.

  20. #20

    Default Re: BF225 overheating at idle but not at higher revs...

    Thanks iang - I’ll check in to that when I order parts tomorrow.

  21. #21

    Default Re: BF225 overheating at idle but not at higher revs...

    Just to close out this thread I have now removed and replaced the corroded oil pan. What a difference this job made to the tell tale (pisser) - before is wa a very half hearted affair - now it is firing out like a race horse! Here is a pic of replaced oil pan...Click image for larger version. 

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  22. #22

    Default Re: BF225 overheating at idle but not at higher revs...

    I ran the engine at idle as before and thankfully no overheat alarm now.

  23. #23
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    Default Re: BF225 overheating at idle but not at higher revs...

    That's OUTSTANDING! How long did it take you to change out the oil pan and get it all back together? Any observations for anyone facing a similar task?
    CHawk 25 DLX

  24. #24

    Default Re: BF225 overheating at idle but not at higher revs...

    It took me a full 3 hours chawk working on a tarp next to the beach to put it all together (so 5.5hrs total disassemble to reassemble completion). Lots of stages to go through but all the steps are explained in the workshop manual you put me on to. I was tempted to reuse the old oil pan gasket but decided against it as the consequences of a leak between the water jacket around the exhaust and the sump arenít worth it. The gasket is pricey but its special in that it is made to deform and form a seal when crushed - hence no reuse. The manual says replace It so thatís what I did. Also the O ring of the oil strainer. I researched the use of a sealant on the gasket but couldnít find any reference to it so the gasket went on bare. The main tips Iíd say is get the water tube grommets nicely greased up: into oil pan, the one through mid section and into the water pump housing. Then just be very methodical - there are no moving parts so this should be considered something a half competent DIYer can have a go at. The dodgiest bit for me was removing the big rubber engine mounts with the 22mm hex head bolts and lock nuts. Hopefully I can keep this old motor running a bit longer...

  25. #25
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    Default Re: BF225 overheating at idle but not at higher revs...

    James t - good explanation. Thanks for that.

    The USCG was putting 5,000 - 6,000 house on these engines. BUT, they were running them almost every day except when they were in the shop for maintenance. So, hopefully, this one will last you for many more hours. Have a good fishing season.
    CHawk 25 DLX

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