96 ST1100 Thermostat O-Ring Needed and Advice welcome

PaulB

Joined
Apr 16, 2024
Messages
4
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.
Click to expand...
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.
 
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