Cooling system

Noticing that the temperature gauge came up very slowly, it was likely that the thermostat on the ST1100 was not working correctly. The costs for a replacement thermostat are low and I decided to replace also most of the old rubber hoses of the system.


01: The coolant in the spare tank was bright green and the level stable. Then seeing this dark and dirty coloured green coming out of the radiator, made clear there was something very wrong...


02: When the old thermostat came out, I checked it together with the new one. They opened both at 82°C.
When comparing both, it looks like the old one has a much larger diameter. It is however not only the diameter that controls the flow, but also how far the valve opens. The resulting openings appear to be roughly the same on both.
For replacement, I used the inexpensive Gates TH03282G2.


03: Even with a cold engine and the valve closed, there should always be a minimal amount of flow for the nearby temperature sensor to read correctly. For this there is a small hole. It is much larger on the old one because of corrosion. I have no clue as to how much influence this has on engine heating up.


04: The other side also shows quite a few signs of corrosion. Though the thermostat still opens correctly, I decided to replace it.


05: Here we see a very clear defect: The hose for overflow to the spare tank is torn. This explains why the level in the overflow tank stayed constant and the coolant there in mint condition.


06: The same from different angle. As a result of this defect, there was constant about 0,5 liter less fluid in the system. Normally at this cap, the system should be filled max.


07: In further pictures you will see a lot of sediment in the system. This was also the case for the inside of the overflow tank. In fact, the sediment was so much that the only way to see the level was through the filler cap. There is a very simple trick to clean the inside of this:
Partly fill with water, add a little bit of sand and shake the lot for a few minutes. Carefully flush out all remains and your tank is as new!


08: Because of the age (not the mileage) of the bike, rubbers may be expected to fail. Coolant hoses are well known and also the rubber O-rings for the connection of the hoses to the cylinder heads.
Seeing a few drops of cooling fluid here, made me place the cooling system hi on my priority list.


09: This rubber did not fail - yet.
Definitely time for replacing!


10: This is where I noticed minor leakage. Seems like a leak was noticed here before and it was repaired with some extra seal material. Well I just replaced the rubber - Now OK.


11: On the thermostat housing we see quite a bit of sediment. Note that the temperature sensor visible at the bottom of the picture is also covered with it. I suspect this was the main reason for the slow response of the temperature gauge!


12: Paint quality of frame and fuel tank is not exactly superior. So, I make use of this opportunity to do some conservation here. (I drive the bike throughout the winter and thus may expect serious corrosion attack. On inspection next spring, I will decide how to deal with that in future.)


13: The overflow tank is now correctly filled with quality G12+ coolant.