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Author Topic: thermostat - water heater connection  (Read 474 times)

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junaido

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thermostat - water heater connection
« on: April 11, 2021, 09:59:14 PM »

I have a M25 engine on my '86 C34. We were attempting to burp the coolant system after replacing the coolant. Based on my research on this board, I decided to pull the water heater loop hose off the thermostat assembly and fill it with coolant. When I went to pull the 3/8" hose from the thermostat the whole fitting pulled out. Apparently it was hanging on by a thread (no pun intended). Attempts to screw it back in were futile. I am wondering if it was the wrong fitting or if I need to tap this hole. Is this fitting a Universal part or can any pipe/fitting place provide the replacement? Fitting in question looks like the attached pic but a lot dirtier.
2nd question, What is this silver/black fitting on the thermostat? Is it a water temp alarm? I noticed a disconnected wire in this same vicinity (the blue colored thing at the bottom of the picture).

Thanks,
Junaid
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1986 #105, std. rig,  Puget Sound, WA

junaido

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Re: thermostat - water heater connection
« Reply #1 on: April 11, 2021, 10:00:06 PM »

pic
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1986 #105, std. rig,  Puget Sound, WA

junaido

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Re: thermostat - water heater connection
« Reply #2 on: April 11, 2021, 10:11:47 PM »

Fitting pic
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1986 #105, std. rig,  Puget Sound, WA

KWKloeber

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Re: thermostat - water heater connection
« Reply #3 on: April 11, 2021, 10:39:12 PM »

Junaid

The hose nipples on the coolant pump and thermostat housing are 1/8” JIS (Japanese Industrial Standard) pipe thread, which is functionally equivalent to British Standard Pipe Taper (BSPT) thread. They are Kubota parts - check the Kubota parts manual for the D850 or D950 engines on the TechWiki site under the Manuals topic.
Did it break off (no thread on your part?) or are the female threads bad?

You might need to put it back in w/ JB Weld or stronger epoxy if the female threads are gone. I really don’t recall if there is enough room, but if so you could tap it to 1/4” NPT thread and use a larger hose barb.

Tho I don’t recommend it, as a practical matter 1/8” JIS is SO VERY close to 1/8” NPT (18 vs 17 thread/inch) that one screws into the other and with pipe dope doesn’t leak. Before I knew they were JIS thread I replaced both hose nipples with NPT street elbows and barbs (see pic)  because I needed to run my hoses to port. Nary a leak there (but again I’m not recommending you mix NPT/JIS threads.)

-ken

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KWKloeber

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Re: thermostat - water heater connection
« Reply #4 on: April 11, 2021, 10:52:22 PM »

PPS.
The OEM terminal has a black plastic holder for the actual terminal end. Your alt shop likely won’t have the correct plastic carrier, but you can cut that slot w/a dremel.

The ones on the Alts are a solid plastic but for the switch you need a slot cut down partway (the plastic slides sideways onto the button):



while on an alt the plastic mates endways:



Or order a pigtail, there’s many around.

https://www.ebay.com/itm/Coolant-Temperature-Switch-Pigtail-Connector-GM-Temperature-Sending-Unit-Gauge-/372943712384

But that type terminal is really sucky for a marine engine application/environment and should ideally be changed.




PS. The other unit is your High Temperature Alarm Switch.   The PO replaced the original M-25 TStat cap (which didn’t have a threaded port for that switch) with the new style TStat cap.
The terminal on the wire is the wrong one, and probably fell off the switch.  A 1/4” quick disconnect terminal is not the correct one, that switch takes a male “Delphi Packard 56” terminal.  It’s the same button terminal that I’ve seen available online as a replacement pigtail for a ‘Vette engine at an ungodly price.  The female terminal is spring-loaded so it stays on and is the same used on many alternator Field connections and so if take the switch you might be able to have a local auto alternator shop make up a pigtail to butt crimp on the alarm wire. 
It’s a PITA terminal that doesn’t belong on a boat. There’s replacement switches that have a 1/4” male tab (quick disconnect) terminal.
« Last Edit: April 12, 2021, 07:47:01 AM by KWKloeber »
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junaido

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Re: thermostat - water heater connection
« Reply #5 on: April 12, 2021, 10:43:29 AM »

Ken,

Thanks for the detailed reply. Really appreciate it. The nipple is not engaging with the hole at all, so JB Weld etc. won't help much. There is plenty of female thread so I think I will try Kubota/Universal dealers in the Seattle area to see if I can find something with compatible male threads (JIS, British or NPT in that order). Hopefully it's not cross-threaded and I can get it back in with pipe dope or something. I will reconnect the water temp connector.
Regards,
Junaid
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1986 #105, std. rig,  Puget Sound, WA

Stu Jackson

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Re: thermostat - water heater connection
« Reply #6 on: April 12, 2021, 10:47:19 AM »

Ken's right about the manuals in the wiki.

It is critical to note that there is a KUBOTA manual for the M25, B6200 tractor engine IIRC.  I use that all the time when I go to get parts for my M25 at my local tractor dealer.  I print the page out and bingo, parts are easy.

FYI, 99% of the XP parts are the same as the M25, at least the ones you are involved with here.
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KWKloeber

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Re: thermostat - water heater connection
« Reply #7 on: April 12, 2021, 11:36:09 AM »

Ken,

Thanks for the detailed reply. Really appreciate it. The nipple is not engaging with the hole at all, so JB Weld etc. won't help much. There is plenty of female thread so I think I will try Kubota/Universal dealers in the Seattle area to see if I can find something with compatible male threads (JIS, British or NPT in that order). Hopefully it's not cross-threaded and I can get it back in with pipe dope or something. I will reconnect the water temp connector.
Regards,
Junaid

The female is 1/8” JST.
The hose nipple is 1/8” JST and you have THE OEM KUBOTA PART.
These are FACTS, not opinions.

If they are not threading together then one OR BOTH threads are worn or sheared off or corroded away (galvanic corrosion.)
The only other size would be 1/4” JST (or NPT) but you’d see that huge difference in size if the PO retapping the port (which I can see it wasn’t.)
From the pic it APPEARS that you might be able to retap the housing to 1/4” NPT for a new hose barb.

If the threads are not engaging because of factors I describe, then YOU DO NEED JB (or preferably a stronger aluminum-reinforced epoxy like Devcon Stu used or there’s others) to mate them back together.

I don’t mean to be curt, but I’ve “lived” that engine for 30 years worth of pain.
YBYC, go ahead and waste your time looking for a Kubota or Westerbeke dealer to get a fitting that works when yours is THE CORRECT/OEM one.  How? Take the engine to them and try different size thread hose barbs?
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junaido

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Re: thermostat - water heater connection
« Reply #8 on: April 12, 2021, 11:42:21 AM »

I am not sure where the JB Weld is applied? Outside the hole? The nipple isn't fitting in the hole.
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Stu Jackson

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Re: thermostat - water heater connection
« Reply #9 on: April 12, 2021, 11:47:19 AM »

I would caution against using JBW on your engine.  While my application was on a stud, there wasn't much pressure involved, but it failed.  I really believe it is inappropriate for this use and highly recommend Devcon, which you can get in small tubes, 1/2 the size of toothpaste tubes, for $15.
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junaido

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Re: thermostat - water heater connection
« Reply #10 on: April 12, 2021, 11:54:45 AM »

I am happy to use Devcon, but just want to understand what you guys are advocating. Just place the nipple at the mouth of the opening with no threads engaged and slather Devcon around it and then put the hose back on? Or get a slightly smaller nipple that goes into the hole so it is a better connection before applying the Devcon?
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KWKloeber

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Re: thermostat - water heater connection
« Reply #11 on: April 12, 2021, 12:20:23 PM »

I am happy to use Devcon, but just want to understand what you guys are advocating. Just place the nipple at the mouth of the opening with no threads engaged and slather Devcon around it and then put the hose back on? Or get a slightly smaller nipple that goes into the hole so it is a better connection before applying the Devcon?

NO!!
From your original post it appears the fitting was IN the TStat then pulled out, so it should go back in.

Ok, first I’d chase both threads with a 1/8” JST/BSPT tap and die.  Then if they mate up (and tighten?) you’re good to go (with pipe dope or PTFE.)

If after chasing the fit is loose or non existent, then use epoxy as you would pipe dope to replace, essentially, the missing thread(s) and “weld-in”’ the fitting in place after you screw it in.

Research the specs on whichever epoxy you use if it comes to that. I’ve seen lice a 10x difference between different “metal replacing” products. I really have no clue where Devcon falls on the scale but it certainly worked (knock on teak) for Stu’s water pump stud.

Another thought (just an option 2 depending on what you find after chasing the threads) epoxy in a bushing that you can screw that or another hose barb into (so you can remove/replace it down the road if need be.)

Option 3, get a new TStat housing (I ass/u/me that part is still available from Kb.  The CAP is Westerbeke not Kb, but the lower housing is Kb.)

Option 4, if able retap the housing port to 1/4” NPT.
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Stu Jackson

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Re: thermostat - water heater connection
« Reply #12 on: April 12, 2021, 12:41:41 PM »

Ken's right, he's giving you the OPTIONS.  Only you can decide what you think you can and/or should do.  Photos can only go so far in showing the actual condition of material.  I'd show you a picture of a nice piece of wood, but then pinch it between my fingers and it'd crumble.  Like that.  Could happen with metal, too.

ITWMB, I'd go for option 3.  There was a recent thread here about a skipper who messed up threads on an application on his boat and eventually admitted that he should have used new fasteners instead of the old ones.  When in doubt, or when replacing something buy new.  Easy for me to spend your money, right?  But if you think about it, we're trying to save you money and aggravation.

Good luck.
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KWKloeber

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Re: thermostat - water heater connection
« Reply #13 on: April 12, 2021, 01:27:58 PM »

BTW if you plug in the Option 3 part number in the parts search at www.Messicks.com it will tell you whether it’s still available and/or any superseded part numbers.
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