Coolant leak at the thermostat housing

Ok, a long story short....................

I am FINALLY hitting the last stages of repairing my crashed FJR from last September when I decided it needed to go bouncing down the Black Rock Playa. This is my FJR#1, the dirty ol whore, and 04 with 95k miles. Last major project is a slight coolant leak I have had since the crash. When I say slight, I mean that in the 4,000 miles I rode the FJR post crash, it never dripped on the ground, and I lost only about an inch worth of coolant in the resevoir. I would smell burnt coolant shortly after start up, and I surmised correctly that small amounts were getting on the headers.

After spending a few hours tracing down the dried coolant trails, I have finally identified the source of the leak. I think. All trails seem to orginate from the bottom of the thermostat housing. In the photo below, its where #32 and #36 join.



So my questions are these:

Does anybody have any idea why this would leak?

According to the parts diagram above, and the service manual (Page 6-9), there is no gasket between the two halves of the thermostat housing. How can this be? I mean there are only two screws holding this thing together for crying out loud.

Has anybody ever had the housing off/apart and know have some familiararity with it?

So far all investigation has been with everything still in place. Why? I am too chicken to start taking stuff apart as this is new territory for me. I am afraid that if I remove the Thermostat Assembly Inlet Pipe (#24) which is required, I will have a new coolant leak worse than the one I have. I know there was a thread fairly recently where re-inserting that damned pipe caused a forum member all kinds of grief.

I guess I want to know that if I do remove all that ****, and take apart the thermostat housing, what the heck am I going to find? What's wrong and how am I going to fix it? And how could the crash have caused it, as it is pretty well protected and isolated? BTW, I ran the FJR today (first time since early January) and let it heat up to 4 bars, where the fan kicked in, and after a few moments, went back down to 3 bars. I let it do this cycle three times. Just a slight amount of moisture on the bottom of the thermostat housing. Not even enough to form even a fraction of a drip.

So I guess my options are to keep on riding and see what happens, try and remove everything myself, and pray I don't f*** anything up, or chance it with a dealer and give my 48 month Y.E.S. it's first try.

Any advice?

Any ideas as to what's going wrong?

BTW, does anybody know what the hell bolt #33 is for? The service manual does not name it, just simply gives a torque spec for it and instructions to repalce the gasket (#34) with a new one.

Skooter - some import cars I've seen use the thermostat as the gasket between either housing. The outer diameter of the T-stat has a rubber 'gasket' that fits around either side. This 'gasket' may have, after 95,000 miles and countless heat cycles later just started to leak.

Hey - this is just a midnight guess. I'll follow the thread and await the true guru's responses.

+1 on the possibility of the thermostat being the problem. Another thought might be the o-ring #31.

Between 32 and 36, there'll have to be a gasket, no other way to prevent a leak. Pull it apart and let us know what you find, you chicken or something?

Looking at the diagram, I'd guess that #33 is a way to bleed any remaining air from the thermostat housing.

Most likely the stat has a seal around it's edge, a flat o-ring if you will, and has an inside slot the stat edge fits into, or it's formed around and an integral part of the stat, hence it's not being shown as a serviceable part. Odd area for a leak however-I'd be more suspicious of the joint between the water manifold and the stat housing, any tweak in this area would definitely cause a leak, as the o-ring has to sit square in the housing to work. Could even be as simple as a loose clamp on the hose though. Simply loosening the bolts retaining the stat housing to the water manifold and twisting the stat housing a bit to make sure it's firmly seated and re-installing the bolts may fix it. Or, make it worse... Sky's right-33 is a top of the system bleeder.

You are such a *****. Just start taking the friggin' thing apart! :lol:

Look, just undo every fastener you can see within an 18-inch radius of the thermostat housings. Eventually, Everything Will Become Clear. :evilgrin:

Re: cause of the leak: who knows, Skoot; it simply may be one of the end results of your FJR going ***-over-teapot. Perhaps the housings got slightly tweaked, etc, etc.

And I wouldn't be patting yourself on the back just quite yet regarding the end of your coolant leak woes.... these leaks can be insidious. You think you found it and got it all taken care of, then, BAM, you get the burning coolant smell again, etc....

SkooterG said:

Does anybody have any idea why this would leak?

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I'm going to go out on a limb here and say its leaking because you bounced it off the playa floor.

Take the SOB apart and look at it!

Warchild said:

You are such a *****. Just start taking the friggin' thing apart! :lol:
Look, just undo every fastener you can see within an 18-inch radius of the thermostat housings. Eventually, Everything Will Become Clear. :evilgrin:

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Or in this case, green

Inconvenient but effective is to add a dye to the radiator then use a black light to look for trails :drag: The poor mans method is to mess up that beautiful '04 of yours and spray the suspect areas with foot powder. Trails will show up almost as good as the dye method. Rad juice will always leak down to the lowest point. Finding green on the bottom of anything is most likely not where the leak is coming from.

Thanks all. I too, was leaning towards the thermostat having some sort of sealing properties.

Warchild said:

You are such a *****. Just start taking the friggin' thing apart! :lol:
Look, just undo every fastener you can see within an 18-inch radius of the thermostat housings. Eventually, Everything Will Become Clear. :evilgrin:

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It's not the taking apart I am worried about. It's the putting it back together!

radman said:

Odd area for a leak however-I'd be more suspicious of the joint between the water manifold and the stat housing, any tweak in this area would definitely cause a leak, as the o-ring has to sit square in the housing to work.

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You know, I considered that area as a source of the leak, but I spent A LOT of time trying to find the source and while I can't see everything, I am reasonably certain that the leak is not coming from there. Still.......

ionbeam said:

Rad juice will always leak down to the lowest point. Finding green on the bottom of anything is most likely not where the leak is coming from.

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An excellent point. But I was REALLY thorough.

Damn. Guess I am going to have to order up some new O-rings and a thermostat and take everything apart. I REALLY don't want to do that, but looks like I have no choice.

#33 being a bleed screw also makes sense and was what I was thinking, but here's the problem: The service manual has ABSOLUTELY NOTHING about that screw or a procedure for bleeding the thermostat housing. So how, and when would you bleed? I mean, I have drained the cooling system several times and never bled the T-stat housing.

SkooterG said:

<snip>So how, and when would you bleed? I mean, I have drained the cooling system several times and never bled the T-stat housing.

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Many cooling systems will self-bleed over time -- if you work on the bike that requires cooling sys. take-apart and you refill with coolant and add to the overflow reservoir; after you ride for awhile (heating and cooling cycles) you may notice that the level in the reservoir went down.....self-bled.

If you were, say, a shop mechanic, you may want to run the bike and open the bleeder to get out any trapped air so that the customer takes a bike that is ready to go and not needing any coolant topping-up later. A lot depends, too, on how much take-apart was done -- an engine disassembly introduces much air to the system.

The circular 'o'rings for the water pipes are easy leakers, easy to damage on assembly, etc -- prime suspects, imo. Ionbeam's correct in saying that spray foot powder is your friend when searching for the source of leaks.

good luck

+1 to caharafamegaa....his post.

Rad juice

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OK, that's disgusting!

Thanks for all the info everybody. Keep it coming.

Question: When one does a valve adjustment, does all this stuff come off? The reason I ask is the one thing I always have the dealer do is the valve check/adjustment and one was completed only 3,000 miles before the crash and the start of the smell of the coolant. Perhaps it took that long for the trace amounts of leaked coolant to reach the header and show the symptoms I encountered?

Last night I cleaned up all the dried coolant trails. And after reading the above replies I spent more time investigating. I really don't think the leak is coming from where either half of the T-stat housing is connected to a hose or the inlet pipe. Though I don't know for sure, I still am reasonably certain the leak is at the housing itself where the two halves join.

This morning, I fired her up again and let her idle for approximately 30 minutes. The cooling system went through several 4 bars/fan activated/down to 3 bars cycles. I even revved it for a little while. The result? No leaks or moisture whatsoever as far as I could see, and I looked hard. So now I am buttoning it back up. I will order the several seals and such and after doing some riding, check everything again. In the mean time I will work up the courage to disassemble it all. I like the foot powder idea, but the areas I need to check won't be accessible with the powder prior to disassembly.

Fuke. I hate **** like this and I have a LOT of riding planned for this bike this summer. Oh well, I hope to have it roadworthy tonight or early tomorrow to go out and road test all the other repairs.

SkooterG said:

Fuke. I hate **** like this and I have a LOT of riding planned for this bike this summer. Oh well, I hope to have it roadworthy tonight or early tomorrow to go out and road test all the other repairs.

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It sucks to be you man!

I read that you were just earnestly getting to this and thought to myself, "Cracked subframe? Mine's back together and I'm now sorting out small stuff like getting a CB to work with my Starcom.....and Skooter is just chasing down a coolant leak from a playa flip? My life is good compared to that poor schmuck!"

They lift the tank and remove the valve cover....I don't think they disturb the coolant system at all.

You really think the leak won't come back? Seems a bit like a teenager promising he won't blow his load in the prom queen.

Is it possible to take the whole unit from your other bike and swap it?

Ignacio said:

It sucks to be you man!

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Yes. Yes, it does.

Ignacio said:

I read that you were just earnestly getting to this and thought to myself, "Cracked subframe? Mine's back together and I'm now sorting out small stuff like getting a CB to work with my Starcom.....and Skooter is just chasing down a coolant leak from a playa flip? My life is good compared to that poor schmuck!"

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No argument there. I am waaaay behind schedule. This stuff was supposed to be done in January. I should be working on other projects now - even have some done. Like powering my tankbag and then Autocomm/Mix-it, and adding a CB. Don't think the CB is going to happen. Or.....maybe I'll mooch off all of your research.

Ignacio said:

You really think the leak won't come back? Seems a bit like a teenager promising he won't blow his load in the prom queen.

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Oh, I think the leak will come back. But I am at an impass now. I am not disassebling until I have all the replacement parts, and hopefully I can further troubleshoot the source of the leak with some new coolant trails. Besides, I need to road test all the other repairs to make sure I don't have any other issues.

Ignacio said:

Is it possible to take the whole unit from your other bike and swap it?

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Unfortunately not.

I am confident that once I disassemble, I can correct the source of the leak. I am just worried about introducing a new one with the stuff I disassemble to get to the current leak. And the same hazards would apply to swapping.

Ignacio said:

Is it possible to take the whole unit from your other bike and swap it?

Click to expand...

I've got a better idea. Swap bikes and use the new bike as your LD steed instead of the bike thats been airborn, bounced off a playa, slid down asphalt (twice), has a "check engine" light that comes on, has this 'funny' situation where the bars are crook, and has a mysterious coolant leak.... of course I already know the answer to this...

If it means anything....when I got my subframe fixed.....a serious weight felt like it had lifted. I'm betting you will too when you figure this coolant thing out.

...except scratch that after Vecter posted. That handlebar thing....is SERIOUS. If you haven't fixed that...he has a very good point.

If you're bound and determined to ride Flipper....that would at least be a good candidate to swap forks. I'm 99% sure you tweaked something serious there buddy.

vectervp1 said:

I've got a better idea. Swap bikes and use the new bike as your LD steed instead of the bike thats been airborn, bounced off a playa, slid down asphalt (twice), has a "check engine" light that comes on, has this 'funny' situation where the bars are crook, and has a mysterious coolant leak.... of course I already know the answer to this...

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Hey now! She may be used and abused and not all that pretty...........but she's a RUNNER!

Ignacio said:

...except scratch that after Vecter posted. That handlebar thing....is SERIOUS. If you haven't fixed that...that would be a good candidate for swap of at least forks. I'm 99% sure you tweaked something serious there buddy.

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That's why I need to road test ASAP. Forks were sent out, measured, and proclaimed "straight". New bushings and seals installed. So I need to get it out and see if my handlebars are still *funny* when going straight down the road. If so, one of the triple clamps is what's bent. But the suspension guru I used told me of a trick to straighten a *slight* misalignment. Regardless, gotta get this ***** on the road to see where I am at.