Suspected overcooling, need help troubleshooting.

[abmup]

Hi, new to the forum and new to owning a thumper.
I' recently bought a xtz660 3yf and noticed that the temp wouldn't climb when driving. At first I just assumed it was a bad thermo unit or gauge so I got replacement parts and installed them. After this didn't fix the issue I got a bit confused and tested the thermo unit and the thermostat in a pot of water on the stove and saw that they were working correctly, the thermostat starts opening at 80~85 C and the thermo unit gives the correct resistance at 100 C. The only way I can get the temp to start climbing is to stop and idle for a while but as soon as I start driving it quickly cools down again. This is with ambient temps of 30 C. The gauge doesn't show any values but the needle is like 1 mm into the large white zone.
Maybe I'm working on the wrong assumptions and these bikes aren't supposed to run any hotter? When checking the temperature on the outside of the water pump with an IR thermometer after driving its around 50~55 C which should be pretty close to the temperature of the coolant which seems way below what it should be. I'm guessing it should be around 80~90 C right? I'd be grateful for any insight from someone more experienced.

[charliext1vj]

If the thermostat is doing its job correctly then I would suspect your gauge? If you leave it running stationary with outriding by nature it must get hot and test/raise your guage - if it doesnt raise then it is wrong - can you measure it differently? All engines running will provide significant heat through the radiator unless you force cooling through air flow such as a fan. No expert but you cant beat thermodynamics!

[abmup]

Yes as I said when I leave it running while stopped the temp gauge will raise and eventually the fan starts up.

I've tested the thermo switch for the fan and it works as it should and closes the circuit at ~105 C. When the fan kicks in the gauge is close to the red zone so I'm pretty sure the gauge is correct.

The only possible cause I can think of that would lead to overcooling is that the thermostat doesn't close properly but it seemed to be working well when testing it outside of the housing. I even put some sealant around the edge to prevent any coolant from leaking around the outside edges as I could hear it moving slightly when shaking the housing around but I don't think this was an issue.

I guess the only thing left is to replace the thermostat but I was hoping I wouldn't have to since the seem hard to find at a reasonable price.

[jibber]

The stat could be acting differently in a closed system, ie: under pressure..

[abmup]

Hmm yeah, that could be it actually. I'll just have to get a replacement then. Well thanks for the input.

[GeoffD]

They all do it, all XTZ660's overcool.... funnily enough I had this conversation with Dave Lambeth a few months ago. To be honest I don't worry about it too much. If it was a problem I'd probably block of half the radiator....

[Jim462]

Had mine from new, 1998, and always run with half the radiator covered, summer or winter in Aberdeenshire. Used to to run cool but now runs about mid temp. Runs fine in a hot English summer as well.

[Ploddit]

Aren't the xt600z 3AJ also affected by over cooling?