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Old 10-22-2012, 05:40 PM   #1
Emrys
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Default Radiator Fan Isn't Kicking On

Couple of months ago I noticed my bike was running a little hot. After inspection, I noticed the fan wasn't kicking on at 220. I jumpered the Coolant Temperature Sensor out so the fan runs all the time. This was a good temporary fix until I could locate a new Coolant Temperature Sensor.

I finally got around to replacing the Coolant Temperature Sensor today and decided to go for a ride. Same deal....fan doesn't cut on at 220. It got up to 240 before I decided to turn it off.

So I decided to check the old Coolant Temperature Sensor for operation. At room temperature it reads approx 25 megaohms. When using my stove to heat it up it reads <1 ohm somewhere past 200 degrees. It was difficult to determine the exact temperature. Nevertheless, it proved it was operating correctly.

I'm kind of stuck on this one. What could cause this? Even if my radiator was clogged, the heat would still transfer to the sensor with the radiator being highly thermally conductive. Any ideas?


BTW, coolant temp is good any other time when riding and the fan working. Normally runs between 160-180 depending on what season it is.
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Old 10-23-2012, 09:06 AM   #2
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So, you used a jumper wire to only eliminate the temperature sensor and this leaves the fan on all the time?

I'm not familiar with the specifics of the temperature sensor and fan system, but if you're sure that's the only component you jumped, that doesn't make sense to me that it wouldn't work.
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Old 10-23-2012, 12:23 PM   #3
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Default overheating

My brothers bike did the same thing, I had to change the temp sensor and flush the radiator. After that the fan comes on at 220. Go to the dealer and get the sensor because its a dealer only item. Good luck
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Old 10-23-2012, 03:39 PM   #4
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Grab your multi-meter and check continuity of the wires going to the temp switch. One should read <1 ohm to ground, the other shouldn't read anything since it comes from the fan. The only thing the switch does is close the fan circuit to ground.

If the switch is operating correctly, I would say either the terminals to the switch or the wires are not connected properly.
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Old 10-23-2012, 05:56 PM   #5
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Quote:
Originally Posted by MHarrisEP View Post
So, you used a jumper wire to only eliminate the temperature sensor and this leaves the fan on all the time?

I'm not familiar with the specifics of the temperature sensor and fan system, but if you're sure that's the only component you jumped, that doesn't make sense to me that it wouldn't work.
A very simple way of describing it's operation would be (where all components are in series):
12V Source ---- Radiator Fan ---- Coolant Temp Switch ---- Ground.

Basically, the radiator fan doesn't kick on until the Coolant Temp Switch reaches a certain temperature (227 F) which acts as a switch, closing the circuit and allowing the fan to run. When the Coolant Temp Switch is cooled off to a certain temp (220F I believe) the switch opens back up, cutting the fan off. Cycle is repeated as necessary.


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Originally Posted by UltimatE View Post
Grab your multi-meter and check continuity of the wires going to the temp switch. One should read <1 ohm to ground, the other shouldn't read anything since it comes from the fan. The only thing the switch does is close the fan circuit to ground.

If the switch is operating correctly, I would say either the terminals to the switch or the wires are not connected properly.
I was thinking the same thing. But the fact that I can jumper the CTS connector plug out, essentially acting as though the CTS reads a temp of >227F makes me believe the problem is downstream of the connector. What do you think?

I think Pistol may be right about the radiator needing flushed. Since I've already verified both sensors to be working within the same range, that seems like the most likely problem. I just have a hard time believing the radiator temp doesn't soak the sensor even with a low flow condition.
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Old 10-23-2012, 06:45 PM   #6
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Quote:
Originally Posted by Emrys View Post
I was thinking the same thing. But the fact that I can jumper the CTS connector plug out, essentially acting as though the CTS reads a temp of >227F makes me believe the problem is downstream of the connector. What do you think?

I think Pistol may be right about the radiator needing flushed. Since I've already verified both sensors to be working within the same range, that seems like the most likely problem. I just have a hard time believing the radiator temp doesn't soak the sensor even with a low flow condition.
You're right, I forgot about that part. I would try giving the radiator a flush and see what happens.

Another thing to think about is the possibility of a faulty temp sender for the gauge. Maybe the bike isn't getting as hot as the gauge says.
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Old 10-23-2012, 08:37 PM   #7
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Originally Posted by UltimatE View Post
Another thing to think about is the possibility of a faulty temp sender for the gauge. Maybe the bike isn't getting as hot as the gauge says.
Ya man, considered that one as well. Kinda ruled it out though after verifying cold engine temp before startup with ambient outdoor temp. (ie: 70F on gauge when it's a 70F day)

I'll try the radiator flush and let you guys know how it goes.
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Old 10-30-2012, 10:56 AM   #8
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So here's an update for you guys. Finally got a chance to remove and clean out my radiator. I inspected the inside but there really wasn't any buildup or dirt in there. But, I decided to give it a good cleaning anyways.

I put everything back together and tested it again. Coolant temperature got up to 231F before I shut it off. So it looks like it isn't the radiator either.

I quickly took a resistance reading of the thermo-switch and it still hadn't opened up. So for some reason the switch is not reading an accurate temperature inside of the radiator. I decided to use an IR pyrometer and noticed temperature around the switch is about 30F cooler than the main coolant inlet to the radiator.

While reassembling the radiator, I came up with another possibility. There is a bypass line coming out of the thermostat housing that connected directly above the thermo-switch on the radiator. It looks as though it may be used to wash down the thermo-switch for an accurate temperature reading. Does anyone know if this is correct? If so, maybe there's a blockage that's keeping the switch from reading an accurate temperature.
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