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Thermostat leaking - vacation Friday - HELP

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Thermostat leaking - vacation Friday - HELP

Old 06-15-2020, 08:46 AM
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Default Thermostat leaking - vacation Friday - HELP

So I have a pair of Honda BF150's on my boat, and one of the thermostat housings is leaking like a sieve, appears to be at the gasket where the housing meets the block. I had this issue "repaired" by a local shop before my recent fishing trip, who felt pretty good that they had made a good repair and it would not be an issue. I went fishing Saturday, and the housing is still leaking. One would think this might be a relatively minor problem, but the air intake is a few inches from the housing, and it is sucking salt water mist into the engine, fouling the plugs (and who knows what else) and then the motor is shutting off.
In order to try and repair, the shop indicates they removed the housing, smoothed and cleaned the metal surface, placed a liquid sealant, and then torqued the bolts that hold the housing in place. All seems like the right steps to me based on reading other threads. I have called the shop to tell them that I still have a problem, and am waiting a reply as to what I could try. I'm handy, so I want to try and fix this myself since I'm leaving for a trip end of week. Any suggestions on how to approach the repair differently?
It seems like this should be a relatively easy thing to fix, I've never heard of this sort of issue not being able to be repaired. It does not appear visually that the metal mounting surface itself or the thermostat housing have defects that would make them leak, although it makes sense to go ahead and replace the housing itself. Only thing I can think to do is make sure and use Permatex for the seal and make sure bolts are torqued correctly. Thanks for any suggestions.

Old 06-15-2020, 08:50 AM
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Is that a plastic housing? Im not familiar with your specific application, but in the automotive world, its not uncommon for the housing to get distorted from heat. if it were mine, I would just replace the housing
Old 06-15-2020, 08:53 AM
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Originally Posted by ktroyer2265 View Post
Is that a plastic housing? Im not familiar with your specific application, but in the automotive world, its not uncommon for the housing to get distorted from heat. if it were mine, I would just replace the housing
Yes, the thermostat housing is plastic and was replaced about 3 seasons ago. If there was a source for an after market metal housing, I would certainly switch to that but haven't found one.
Old 06-15-2020, 09:32 AM
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Originally Posted by ktroyer2265 View Post
Is that a plastic housing? Im not familiar with your specific application, but in the automotive world, its not uncommon for the housing to get distorted from heat. if it were mine, I would just replace the housing
So I went online and ordered every part I can see that might be a problem. The assembly comes with a gasket that fits in a groove on the underside of the thermostat cover. Sort makes me wonder if I should leave off the Permatex liquid gasket since it is not part of the required assembly from the manufacturer......?
Old 06-15-2020, 09:40 AM
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ask the shop for their opinion first
Old 06-15-2020, 10:00 AM
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On my car I used gasket with sealant, what will it hurt?
Old 06-15-2020, 10:19 AM
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If the surface of the block/head where the thermostat housing bolts up to is anything but perfect use the Permatex. Often on raw water cooled engines you will see pitting on sealing surfaces like this and a bit of Permatex Aviation or OMC/Evinrude gasket sealer or Merc Perfect seal will make it seal fine. I put the sealer on the threads of the bolts too and have not had seizing problems even in salt water.
About the plastic housing, put a straight edge across the sealing surface after cleaning it up and see if there is any daylight showing through. I use OMC gasket sealer on thermostat housings, bolts, impeller housing gaskets, all the bolts on the outdrive etc. Even when I replaced the water pump on our '98 Jeep about 10 years ago and when I replaced the thermostat about 3 years ago.
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Old 06-15-2020, 10:33 AM
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That isn't under any pressure, the leak is likely due to corrosion on the thermostat housing. A good RTV sealant like Permatex Ultra Black with adhesive and gap filling properties should fix leaks from corrosion. Take the cover off and clean off everything the "shop" put on there and re-assemble using Ultra Black.
Old 06-15-2020, 11:43 AM
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+1 on the ultra black. I had to swap a thermostat on my boat out on the water. The gasket was trashed and I used that. It worked great.
I am not sure how long it is supposed to cure but we were running about a half hour later.
Old 06-15-2020, 12:15 PM
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I’ve had two sets of Honda’s 2006 and 2016. They always had this problem even new. I use Honda bond under the spacer block to head and a new gasket for the cover. Make sure to grease the rubber gasket for cover. Use Honda bond for base spacer block. Let it set up for a day and you should be good.
Old 06-16-2020, 08:19 AM
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Originally Posted by jayyy View Post
That isn't under any pressure, the leak is likely due to corrosion on the thermostat housing. A good RTV sealant like Permatex Ultra Black with adhesive and gap filling properties should fix leaks from corrosion. Take the cover off and clean off everything the "shop" put on there and re-assemble using Ultra Black.
Originally Posted by gfretwell View Post
+1 on the ultra black. I had to swap a thermostat on my boat out on the water. The gasket was trashed and I used that. It worked great.
I am not sure how long it is supposed to cure but we were running about a half hour later.
Originally Posted by capecod26 View Post
I’ve had two sets of Honda’s 2006 and 2016. They always had this problem even new. I use Honda bond under the spacer block to head and a new gasket for the cover. Make sure to grease the rubber gasket for cover. Use Honda bond for base spacer block. Let it set up for a day and you should be good.
Thanks for the guidance! Going to start tackling this tonight. I have the Permatex and will be sure to grease the Honda gasket. I really hope I can get this fixed and enjoy vacation!
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Old 06-16-2020, 09:11 AM
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Ultra black is great for metal to plastic and ultra grey is great for metal to metal. As stated before, I would still add some ultra black to the new housing and gasket

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