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Radiator fan not coming on


Duc2V4

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So here's one that has me a bit puzzled. Report of cooling system issue. Client claims smells coolant burning. On initial investigation, found a few hose clamps that did not seem to be tightened up as the others. Tightened them up and did a pressure test and viola, no leaks. Although I did not do the pressure test prior to tightening, but none the less every looked good.


Second complaint, bike overheats. Hmm, OK possibly bad sensor. I tested the lead to the fan by shorting it to ground and it proved to work, switch did not. I'll replace it. Just for good measure, the thermostat too, in case it's not working correctly.


Third complaint, wax idle unit not working. OK, here too I'll replace it.


After replacing the 3 components, (T-stat, wax idle unit and sensor switch), I buttoned everything up and did another pressure test. Everything came back as good. I ran the bike, did a throttle body sync and let her warm up. Temperature went over 200F and still no fan trigger. I started to hear coolant overflow in the reservoir but again no fan. While it was in this high temperature level, I did the short to ground test on the fan wire and sure enough, fan came on.


Am I missing something simple here? Other than a wire/connector not making contact, I don't know what else it could be. Had a long day up until the final temperature test so called it a day. I looked at the wiring diagram tonight to see how things are connected but have not double checked the bike yet.

 

Anyway, figured I'd post up here in case someone else had and resolved this issue.

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Surely you have a temp gun. Check temps at the radiator in just below the cap, cylinder head outlets, fan switch, and the water pump outlet. Don't trust the gauge.

I had a a fan switch go bad on one of mine. Ordered a new one, and it was bad too. No return on electrical parts so I just installed a manual fan switch on the left handlebar.

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Hi Duc2V4.

Fan not coming on just over 200degF (93degC) is possibly nothing too concerning, for a 6gen fan switch on is anything between 208 to 216degF.

 

Wonder if you have some air in the system, did you purge and top up the system?

 

Just make sure the body of the fan thermoswitch is in fact bonded/grounded back to the battery Negative terminal, zero ohms to the negative terminal.

 

Make sure the "Ground Eyelet" for the left side radiator is clean and tight, and making a good ground connection. (Again referring to 6gen?? 5th is probably much the same). Hope this helps.

Cheers.

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1 hour ago, Grum said:

Hi Duc2V4.

Fan not coming on just over 200degF (93degC) is possibly nothing too concerning, for a 6gen fan switch on is anything between 208 to 216degF.

 

Wonder if you have some air in the system, did you purge and top up the system?

 

Just make sure the body of the fan thermoswitch is in fact bonded/grounded back to the battery Negative terminal, zero ohms to the negative terminal.

 

Make sure the "Ground Eyelet" for the left side radiator is clean and tight, and making a good ground connection. (Again referring to 6gen?? 5th is probably much the same). Hope this helps.

Cheers.

Definitely purged the air. One thing I make sure I do. Going to check wiring and grounds. I’m hoping new sensor/switch is not the culprit.

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2 hours ago, MBrane said:

Surely you have a temp gun. Check temps at the radiator in just below the cap, cylinder head outlets, fan switch, and the water pump outlet. Don't trust the gauge.

I had a a fan switch go bad on one of mine. Ordered a new one, and it was bad too. No return on electrical parts so I just installed a manual fan switch on the left handlebar.

I do have a temp gun/gauge may look at using that to double check actual temp. Thanks

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17 hours ago, VFR750F3 said:

When you purge make sure motorcycle in only on its kickstand and not on the centerstand.

Definitely on that page as well.

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  • 2 weeks later...
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Well, not sure what the deal was but looks like things are working like they are supposed to. Actually took a while for the bike to get above 200F, so I am liking that. Also changed the radiator cap for good measure and that was really the last and only change that I did from the time I noticed the fan not coming on. Well, that and now it officially has coolant in the system not just distilled water. I did make sure the sensor switch was grounded, took an ohm meter and checked the body of the switch with frame ground and viola, had continuity.

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