96 ST1100 Thermostat O-Ring Needed and Advice welcome

PaulB

Joined
Apr 16, 2024
Messages
6
Age
63
Location
Malden
Hi all,
I received my OEM thermostat from Japan but unfortunately it didn't come with the O Ring. Does anyone know where i can pick one up, or an exact fit from another source? I've been having a temp issue whenever the bike is stopped in traffic; it steadily rises to the top red indicator. I can't see where I'm losing fluid but I have to add about 6-8oz of coolant every few months. I replaced the the overflow hose and the radiator cap, snugged down every clamp but no luck so I want to give the thermostat a shot. I tested it with a pan of water and a temp gauge. It opens and closes at the correct temperatures but at full opening it 's supposed to be about 5/16" minimum and it's less . . . maybe 3/16"
Thanks
 
One other thing that I would check is the fuse for the fan in the fuse block and make sure that it is seated properly. Sometimes even oxidation on the fuse can impair current flow and knock out the fan (this happened to me on the 94 and it ran the temperature all the way up to the red, but not into the red when I was sitting in traffic- happily, it was not leaking any coolant, and it turns out that the fan simply was not working when it was supposed to. I think the fan switch was fine, but I did a modification to it anyway). So the first thing I would do is probably make sure you have the fan running when the bike is sitting and warm. What I did with mine and I think others have done too is I ran an electric line from the wire on the fan switch and ran it back to the negative on the battery. It has a switch in between and this way if I’m sitting in traffic, I can manually turn on the fan, but if the switch is still good, it should still trigger when you’re seated in traffic and the bike starts to heat up because of lack of airflow. Since you bought the thermostat, it probably is reasonable economy to switch it out however, I am not sure of the O ring size necessary. Are you still losing coolant despite changing the radiator cap? Sometimes if the cap is going bad and it can’t hold pressure, you may leak out a small amount of fluid over time.
 
PaulB said:
I can't see where I'm losing fluid but I have to add about 6-8oz of coolant every few months. I replaced the the overflow hose and the radiator cap, snugged down every clamp but no luck so I want to give the thermostat a shot.
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That is a significant amount of loss over such a short time-frame. Needing to add that much anti-freeze indicates that there is a leak. Changing the thermostat may improve the temperature control but it won't stop the leak. If you see no evidence of anti-freeze anywhere then it is leaking on to a hot part of the engine and being burned off (evaporated) before it can make it to anywhere visible. Do you ever get the sweet smell of hot anti-freeze? If there is no external leak then the other possibility is that it is leaking internally and being burned in the cylinders. Do you ever see an unusual amount of white smoke exiting the exhaust, or is your engine oil foamy or milky colour looking?

Where ever the anti-freeze is going it is a good idea to figure it out and repair it before it causes more damage or leaves you stranded somewhere.
 
There is another issue I failed to address…did you pull the carbs (time consuming but not that difficult), examine the hoses under the carbs and the metal elbows and O rings (I guess if you could snake a bore scope in there that could work too, but it’s probably pretty tight under the carbs)? These bikes are pretty old now, so those are other potential leak points despite tightening the clamps, and as Andrew mentions, the potential of a head gasket leak internally (although these bikes are really not known for that). Might be worth a look. Some have had the original hoses bulge, then rupture, and leave you stranded.
 
Thank you all for your help. I ordered the O-Ring and also a set of hoses (4) on Amazon for $50. And I’ll take another look at the water pump housing for evidence of a leak. I’ll keep you posted and hopefully I’ll be riding again in confidence and ease again. Thanks again.
 
Since we have had fuel hoses supplied with aftermarket fuel pumps that are not rated for immersion in gasoline sold by Amazon, I have to wonder if hoses for the cooling system are rated for their use. @Uncle Phil - do you know if Amazon's cooling system hoses are ok?
 
SMSW said:
Since we have had fuel hoses supplied with aftermarket fuel pumps that are not rated for immersion in gasoline sold by Amazon, I have to wonder if hoses for the cooling system are rated for their use. @Uncle Phil - do you know if Amazon's cooling system hoses are ok?
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If you are talking about the silicone ones, I'm waiting to see if Martin across the pond gets good service out of his.
It appears that most of the ones on Amazon are silicone.
If the Amazon ones are made in China (probably given the various manufacture names), they could be really good or really bad - it's a roll of the dice.
**EDIT- It appears that the ones on Amazon from Zap Technix are from a German company which makes them much more attractive for me!**
**https://www.mefoshop.com/zap-technix** (assuming it is the same company).
I don't have a clue as up to this point I have always used Honda OEM ones.
Matching to similar automotive type hoses is a real trick that takes quite a bit of time at a local auto parts store and one that will allow you to go back to their hoses and poke around.
For all the work it takes to change them (particularly the ones under the carbs) I would be hesitant.
The upper and lower radiators are not too bad but require some major bodywork removal to get at them properly.
The idea of losing a coolant hose on one of my long trips makes me shutter ... ;)
 
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SMSW said:
Since we have had fuel hoses supplied with aftermarket fuel pumps that are not rated for immersion in gasoline sold by Amazon, I have to wonder if hoses for the cooling system are rated for their use. @Uncle Phil - do you know if Amazon's cooling system hoses are ok?
Click to expand...
I don’t actually.
Uncle Phil said:
If you are talking about the silicone ones, I'm waiting to see if Martin across the pond gets good service out of his.
It appears that most of the ones on Amazon are silicone.
If the Amazon ones are made in China (probably given the various manufacture names), they could be really good or really bad - it's a roll of the dice.
**EDIT- It appears that the ones on Amazon from Zap Technix are from a German company which makes them much more attractive for me!**
**https://www.mefoshop.com/zap-technix** (assuming it is the same company).
I don't have a clue as up to this point I have always used Honda OEM ones.
Matching to similar automotive type hoses is a real trick that takes quite a bit of time at a local auto parts store and one that will allow you to go back to their hoses and poke around.
For all the work it takes to change them (particularly the ones under the carbs) I would be hesitant.
The upper and lower radiators are not too bad but require some major bodywork removal to get at them properly.
The idea of losing a coolant hose on one of my long trips makes me shutter ... ;)
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It is the Zap hoses from Germany. I have most of the bodywork off already so I’d rather change them along with the thermostat as part of the elimination process. I really appreciate everyone’s input here.
 
ST1100Y said:
Currently out touring, none has blown yet
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I'll be really interested to see how they hold up over a bit of time.
I have a lot more confidence in their quality since they are German made and not Chinese made. ;)
It is not that China cannot make quality, it is what the 'requestor' is willing to pay ...
 
Uncle Phil said:
I'll be really interested to see how they hold up over a bit of time.
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Any production in the EC would likely drive prices beyond the OEM range (if even possible with all the environmental and work hazard overregulation in place...)
As said, after the few weeks commute and the current tour they still look like new...
So does the braided silicone line used for the internal bypass...
No leaks, no dripping, no scale building up, no swelling...
 
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