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Discussion Starter #1
Hi there,

going on a moto-camping trip in two weeks but an old problem resurfaced and it stresses me out. My bike is coming back from the garage, where I indicated to the mechanic that I have slight overheat problem. He changed the thermostat, the temp. sending unit and added new Prestone. Everything seemed to be working just fine. It was pretty hot back then (like 30 Celcius/90-95F) and even at idle the gauge would barely get past the large line.

Yesterday, while going to my buddy's house to plan the trip, my temp gauge went between the M and the P again, near the red line. It's beginning to get cold here in Montreal, like 15 Celcius (+-60F) So I don't quite get how it would overheat NOW.

At a red light, all of a sudden, it began to drop where it went after the garage stop, as usual.

So my question is. Apart from a faulty thermostat and temp. sending unit, what can cause this to happen and how can I fix it ? I suspect the fan to just not start early enough but I don't quite get what would be causing that. Could it be clogged, needing to be bleeded again? Is it just a faulty read and I need not to be worried? I don't know but any intel would be appreciated!

Thanks
1982 cx500C
 

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The fans on these bikes is mechanically driven, attached directly to the cam.
So, if your bike is running, the fan is spinning.
They are old (brittle) plastic, and have been known to crack, or even catastrophically fail.
Some vehicle designs are harder to bleed than others, my CX500C that I recently rebuilt, bled right up without issue.
I may have gotten lucky, trapped air in the system can be a problem.
I would consider shooting an infrared temp gun, right at the sensor head.
my bike just hangs at 73 C when I'm cursing around, slightly higher at a stoplight.
I like Doug's answer, I have an aftermarket gauge that runs on 12v.
I forgot that Honda uses that 7v system, just for the temp gauge.
 

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Discussion Starter #4
Thanks for the quick feedback.

I'll look for the regulator.

My fan is actually ok. The temp. sending unit, seal and thermostat are actually parts I bought last year for that exact problem along with a brand new fan. In case these would be the source of the problem I had before sending my bike to the garage. So I do have a brand new fan in case, but after inspecting the one I have now, I decided I didn't need to change it yet.

I could re-bleed the rad. Not a big deal and it might actually help. I ran some rad cleaner twice last year thinking my water cooling system could be clogged with old residues or something. My guess is that it is now ok. But maybe not.

I'll look for an IR gun too, thanks for the input!
 

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I doubt you need to “bleed” your radiator. The cooling system is very basic and small and they generally bleed themselves out. Just make sure your coolant level in the expansion tank is correct. Murray sells a heavy duty 7 volt regulator that will most likely outlast the bike. That’s the one I bought when mine went bad. An IR gun would definitely be useful so you can see if you really are over heating or not. The fact that your gauge moved quickly to the normal range tells me it’s your regulator also.
 

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Any evidence of a slow leak at the weep hole? Has your coolant reservoir level risen?
Unit I Shepped in a new mech seal this spring, the Grub would run a bit warm. I believe it was sucking in air through the mech seal at cool-down, rather than drawing coolant from the reservoir. If I topped up the radiator, it would behave for a while, but eventually started to run warm again.
 

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Discussion Starter #7
Just ordered the 7V regulator on Murray's website. Hope it will arrive before my vacations. Tried to look online for a how to video. It seems like a job I could do.

I'll try to look for the reservoir level, but this thing is so badly placed I rarely see anything!

Thanks again for your help
 

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7 V regulator likely.
Checking the coolant level at the radiator-not the overflow bottle might be useful (especially if coolant recently changed)
Also if I recall theres a grounding wire at the thermostat housing-?disturbed when the thermostat replaced-tho I need to think if that bad connection would give a high or low reading...:unsure:
 

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have you considered that your radiator might be blocked internally ? Theres a bunch of products that will chemically clean the inside of the core - vinegar is as good as most and way cheaper....
 
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Discussion Starter #11
Little head's up. So I proceeded with the 2000 km trip even if I had not recieved the regulator.

Everything went fine until my gauge went above the red line. Stopped and called my mechanic, who reassured me that if my overflow bottle wasn't abnormally filled and I was able to touch the motor without burning myself that everything should be okay.

Stopped by a garage on the way nonetheless, made him get the temp reading at the entry and the exit of the radiator, everything was on spec except for the reading on the gauge so yeah. Regulator.

@bahn88 : didn't know that, might check this out if the new regulator doesn't fix the problem, thanks!

@muzza : I thought my rad might be dead so I bought another one from a member here. Still haven't used it yet because I think mine is still fine. I ran a couple of prestone cleaning bottles last summer + soaked my rad in vinegar for almost a week. Pretty positive a clogged rad is not it by now.

(If anyone is planning a trip next summer, I highly recommend la Gaspésie. Great views, great people, and great food (if you like lobsters and shrimps))

203295


Cheers
Julbrusch
 

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Looked like a nice trip, glad you both made it ok!
 

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FWIW, there is no ground wire to the thermostat housing. In fact, the temperature gauge sensor is screwed into the thermostat housing and its circuit finds ground through the housing and the engine block. It is fairly common for people to bump the wire while working on something in that vicinity and disconnect the wire from the sensor but when that happens the gauge does not read at all until it is reconnected.
 
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