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Discussion Starter #1
Just changed the coolant in the SV last week. I'm pretty sure I bled it well but now I have my suspicions. I'll pull the upper fairing tomorrow to acces the radiator fill to check it again but I thought I'd pose this scanario and question....

Since I went with Blue Ice coolant, I have been paying far more attention to the coolant temp on the gauge than ever before. I am noticing a cooler temp on average. It runs in the low to mid 180's when it used to run in the low to mid 190's on average. Could be the coolant, could simply be the change from 6 y/o OEM coolant to new.

What I'm seeing now is pretty unusual fluctuations that I don't recall seeing before the change. Temp will read about 185 and will bounce around a little up to 188 then down to 184, 183...all close to the average and what I would think is normal but then it will suddenly drop to 170, 173 for a breif moment and then back up to those average mid 180 averages.

Maybe this is normal and I just never noticed or do I have an air bubble in the system causing the sudden drop?
 

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Hi Oh My Sack, I ride on the streets and my temp does jump around with stop and go traffic. If its cold out the temp runs around 166. Seems like 170 / 180 is the norm, when its hot out stopped in traffic I've seen it just over 200.
 

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Thats the temp system at work. Its design to keep the bike around 180-188.

If engine gets lower then 180 it will STOP the flow of liquid through the block allowing it to warm up.

If engine gets above 188-190 It will ALLOW the flow of liquid through the block allowing it to cool down.

If engine get above 212-220 It will KICK in da FAN.
 

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Discussion Starter #4
Thanks.

I'm highly aware of the cooling system's functions. Perhaps my question was to nebulous so I'll rephrase...

Is the sporadic anomally of the 170 spike typical with your readings?

Again, it's not gradually dropping from the mid 180's down the scale to the low 170's, it's going from a near constant 185 and then suddenly 172, 173, 170 for a moment then spikes right back up to those constant mid 180's.
 

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Mine does the same exact thing. If in cooler weather in town(not stop and go 20 feet) when the thermo opens the system drops to 170-173 then climbs back up. This shows me the thermo, temp. sensor, and gauge is working at least.
 

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As long as it's bouncing around in the lower ranges all should be well. I would only start to worry if I saw it doing unexplained jumps at higher temps.
 

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Discussion Starter #7
Pulled the upper fairing and added a small amount to get it back up to the proper level. I guess there was a bubble in there since it was able to take a bit more fluid and it wouldn't on initial fill up. I attempted to burp it again but she wouldn't belch this time so that may be the issue. I didn't ride her today but will tomorrow so I'll compare readings.
 

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I guess when you say you "burped" it that you already knew to rock it back and forth after adding fluid the first time. It's a good idea to start up and let run a while, cool back down and rock it again to check that fluid level remains at proper level after filling. Sounds like you did all that, though.
 

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Same thing happens to my bike as well... bouncy temp numbers.
The only time it stabilizes somewhat is at freeway speeds.
The numbers will stay between 188- 191
 

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Mine did the same thing when I switched to Blue Ice. I burped, bled, cussed and kicked the radiator over a period of several days to make sure there weren't any bubbles. I still get the constant jumps in the temp, everything seems to be running just fine.
 

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I'll expand on the explanation above.

The temperature indication is not engine temperature. It's (roughly) the temperature in the radiator. Temperature indication is relatively slow, far from instantaneous.

The thermostat in the aluminum housing between the cylinders controls coolant temperature in the engine. When the coolant in the engine hits the set point the thermostat opens, coolant flows from the engine to the top of the radiator to be cooled, from bottom of the radiator to the engine to cool it. This fresh coolant cools the thermostat down and it closes. In this period the temperature indication will fluctuate.

If the engine gets hot enough the thermostat will cycle more often or even stay open all the time. The temperature indication will appear higher, but steady. When it gets high enough the fan will switch on. If it gets way too high the high temperature warning will light up.
 

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Discussion Starter #12
Well, I'll see how it is today when I ride.

I'm getting the impression from some of the responses that maybe my point isn't clear...then again, maybe it is and I'm not interpreting the answer correctly.

The 170* downward spike from the constant mid 180's temp isn't something that lags at that temp. It'll be registering a slight fluctuating temp bouncing back and forth from say 183 to 186. It'll maintain this typical fluctuation for maybe 20-30 seconds and then all of a sudden spike down to 170* for about 2 or 3 seconds and then immediately spike back up to the 185's where it remains constant for another period.

My interpretation or visualization of what might be happening is there is constant contact between coolant and sensor in the closed system. As a bubble or void comes across the sensor, given that air is not a good conductor of heat, the sensor spikes a lower temp reading for that pocket of air but then spikes right back up to the 180's as soon as coolant is back in contact with the sensor. It's a 10-15 degree spike which is substantial, IMO.

Since it's occuring while riding, I can't sit there and watch it and time it's cycle to see if there's a pattern. Again, I'll watch for it today since I was just able to add a bit more coolant which indicates to me that there had to be a void in the closed system upon my initial fill up.

Thanks for the replies.
 

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Check the connections on the sensor. There is no way, even with a bubble in the coolant, for temperatures to spike that fast. Even if they did, the sensor is slow to respond. I'd suspect a loose wire, dirty connection, etc.
 

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This fresh coolant cools the thermostat down and it closes. In this period the temperature indication will fluctuate.
not really. fresh coolant never gets to thermostat. it gets to engine first, takes engine heat and than gets to thermostat. so you always get hot coolant to thermostat, right out of heads where coolant reaches highest temperature.
what keeps this temperature lower is ambient temperature and wind that gets to radiator and motor. cooler the ambient temp cooler will coolant be, proportionally everywhere, in radiator and engine.
trigger for fan is on radiator itself and has nothing to do with thermostat. it will ground fan when preset coolant temp is reached in radiator. reason is you don't want to hot coolant coming to engine, it would not do its job.
 

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I'll expand on the explanation above.

The temperature indication is not engine temperature. It's (roughly) the temperature in the radiator. Temperature indication is relatively slow, far from instantaneous.
fyi. temperature indicated on gauge is engine temp, or to be exact temp of coolant that just exited hottest part of engine, head.
sensor on thermostat housing has only one function, it displays coolant temperature on your gauge. it does nothing else.
 

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As long as it's bouncing around in the lower ranges all should be well. I would only start to worry if I saw it doing unexplained jumps at higher temps.
this kind of attitude is what leads to more critical problems while your riding.

to the op, i understand what your saying. if burping it doesnt clear up, i'd say theres something wrong with the stat.
 

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When the thermostat opens the hot coolant inside the engine flows to the radiator. So the indication you see is (roughly, like I said) the temperature of the coolant in the radiator. More on this a little later. That coolant had to be hot enough to open the thermostat. If the heat load isn't too high the coolant from the bottom of the radiator (now cooled down) enters the bottom of the engine (roughly). It flows up through the various passages eventually past the thermostat. Again, if the heat load isn't too high the coolant flowing past the thermostat will be cool enough to cause it to close again.

During cycling like this the temperature reading will go up and down. Up is the coolant in the engine heating up. Down is when cooler coolant reaches the thermostat.

If the observed temperature is relatively high and steady then the heat load is such that the thermostat never closes. In this cycle the coolant in the radiator and the engine are approximately the same. The residence time in the engine is not long enough to raise the coolant temperature substantially. At some point the temperature will be high enough to trigger the fan thermostatic switch and start the fan.

If the temperature continues to rise the high temperature warning triggers.
 

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If the heat load isn't too high the coolant from the bottom of the radiator (now cooled down) enters the bottom of the engine (roughly).
roughly how low?
it enters water pump which is at middle of engine and from there straight to middle of cylinders. other than passing through pump coolant never sees any part of engine lower than upper half of cylinder.
 
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