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Discussion Starter · #1 ·
So I just finished replacing the thermostat in my wife's 79' CX500D. It had a small leak when it was cold as well so I replaced all of the thermostat housing o-rings as well. It seems that the leak is gone, or atleast I believe it is. I took it for about a 7-10 mile test drive and there was no dripping when I pulled it back in the garage.

As a side note I did use the thermostat from an 80' model Honda Civic. I read here in the forums that was acceptable. Comparing the 2 side by side they were identical. Temp rating was the same for both of them as well, 180 degrees. Not sure if that makes a difference but thought I would add that piece of info.

I did however notice that on the ride the temp gauge was reading hot and didn't drop back down. The motor is not making any odd noises and is running great from what I can tell, but I am worried about that temp gauge.

In the morning I am going to double check the radiator level and take it to the car wash up the street to pressure wash the engine down to remove the antifreeze I spilled in the process of removing the housing.

Does anyone have any additional thoughts as to what would cause that temp sensor to read high?

Any help or thoughts would greatly be appreciated.
 

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Did you burp the cooling system?

Often when filling a CX cooling system from empty they don't fill completely due to the thermostat etc. being so high on the motor.

It's best to run the bike until the thermostat opens with the radiator cap off. Sometimes when doing this the rad will overflow when the air comes out, sometimes not. If not you can tell when the thermo opens as the chrome tube will become hot.

After doing this allow to cool then top up the radiator and fit the cap.

If the system isn't full it can run hot.
 

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Check to make sure the leak is gone and wasnt coming from the weep hole (bottom of the water pump housing). As indicated above, make sure the coolant level is ok and all air is out of the system. If it still reads high, there are a couple of things you can check just to eliminate them.
- Make sure the 7V regulator is working ok
- Check the fan to make sure its spining and tight
- Make sure the rad fins are clean and clear, as the bike temp will go up as airflow is restricted.
 

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Discussion Starter · #4 ·
I did not burp the system, never even thought of that. I am going to pull the tank again to top of the antifrreze shortly. Hopefully that it my issue. I know the fan is spinning, I saw that yesterday as I was checking for leaks. I'll let you guys know what I find after burping the system.

Where would I check the regulator?
 

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Discussion Starter · #5 ·
So I tried to burp the system today. This is what I have done so far.

I replaced the 80 Honda Civic Thermostat with the proper Honda CX500D tstat from the dealer.

Everything runs great and my original leaks appear to be great. The temp gauge however is still showing hot after a few minutes and stays there. The lower left pipe (bottom radiator pipe) stays cool which makes me think the tstat is not opening. So now I am thinking either the impeller or the radiator needs to be rebuilt.

I looked on Partzilla and they don't offer a replacement impeller since it isn't produced by the factory anymore.

Tomorrow morning I will begin pulling the pump housing to see what shape it is in.

Does anyone know where I can get a new impeller to replace this one if that is the case... or if you have other ideas as to what my issues could be that would be great.

Thanks
 

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Before you rip anything apart - can you get a laser/infra-red thermometer and check the temp of the radiator when running. Go for a ten minute ride then check the temp at say , the top tank by the filler neck. Then compare to the reading on the gauge. I suspect you have a wiring problem with your 7-volt regulator , more than a mechanical issue , specially if this problem has only happened after you fitted a new thermostat.
 

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Get a meter and do a quick check of the temp gauge circuit. Locate the temp sender unit (on the water pump housing) and remove the wire from it (think its Blue/something). Measure the voltage on this wire to a good bike ground. You should see 7V on it (anywhere between 6.95V and 7.05V). If its outside this range then the 7V regulator is crap. If it reads ok then check the actual engine temp when warmed up (laser temp gun works great for this, check at the cylinder head). If the bike IS getting too hot then you will see it, if its not and the gauge still shows really hot, its probably the gauge itself thats starting to crap out.
 

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Also check wire from temp sensor.
Before you spend any time/money on anything else make sure you plugged the wire onto the temp gauge sender on the thermostat housing.
 

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Discussion Starter · #11 ·
Wires are all plugged in. I will check the voltages this afternoon when I get home from work. If ti was just a regulator issue that still wouldn't explain why the lower radiator pipe is remaining cool to the touch when the engine is showing hot I don't believe right?
 

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if the gauge is "lying to you" then that would explain the cool lower rad hose. It would mean that the bike is running properly and the fan is keeping it cool but the gauge is reading wrong
 

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Best to be sure the gauge is reading OK, as if it is and the lower pipe isnt getting hot, either the thermostat isnt opening or the impeller isnt moving water properly. You will know once you validate the 7V regulator, and if its OK then I would be concerned about improper water circulation which if left unchecked can toast the motor
 

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Hi Had a similar/exact problem, and considered all things you may be about to do or have already done, but checked the regulator first and it was the 7v regulator, mine was hidden in the little factory fitted clock fairing/case, about as big as a matchbox, if your handy with a soldering iron then build your own, I built my own replacement using a couple of purchased parts from Maplins costing 6 pounds, I had the simple circuit off one of the forums on this site, search for it as I did, would love to put a link on here but computers aren't my thing....sorry. A replacement regulator, if you can get one, will cost you £50-£60 in England so is worth considering. Good luck.
 

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It would seem odd that the cooling system was ok before the repairs and not now so the radiator and water pump did not change and might indicate they are still good. Is it possible to put the T'stat in upside down on these?? I believe it goes spring side down. Could the temp sender wire be pinched somehow during/after the repair? Just thoughts??
 

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If the gauge is reading anything then the wiring to the sensor is intact (gauge would read nothing if the wire was off, and would pin and kill the gauge if it was shorted to the frame). the only thing that will give bad readings is a faulty sender (unlikely), a bad 7V regulator (possible) or a problem with the actual water circulation (probable). Since you replace the thermostat I would sure start there, especially if the side water pipe isnt getting hot. Recommended the 7V check as its fast, easy and doesn't require pulling anything apart.
 

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Discussion Starter · #17 ·
So I bought a small infrared thermometer today to check my heating issues out. I checked at the top of both cylinders, top of the radiator neck, exhaust ports, thermostat, rigid water pipe and center of the motor. Highest temp anywhere was about 195F and that was at the exhaust manifold. I let it run for a solid 30mins in my garage with no fluctuation in temp and no leaks anywhere (happy dance).

Gauge still showed as being hot.

I put my digital MM on the wire going to the tstat and it showed 7.4V so I decided to take everyones advice and check the regulator. The bottom of the 7V regulator was a small pile of rust, cracks all in the regulator housing etc etc. I am going to assume it is bad and the 7.4V was causing the gauge to creep up to the hot side of the needle. Oh also the rigid coolant pipe on the side is getting hot now so I am fairly sure the impeller is fine and the tstat is opening as it is supposed to.

I am about to head out to a local electronics store to pick up a 7805 regulator so I can build my own replacement. I have a question on the green LED however, I know it needs to be 5mm but is it a 3v or 2v that I am in need of?
 

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The colour of light produced by an LED is determined by the junction material, which also determines the junction voltage. Almost all green LEDs drop 2V.

See if you can find a 7807 regulator instead of a 7805 (the last 2 digits indicate the regulated voltage). When Reg developed his circuit for the replacement regulator 7807s were pretty rare but 7805s were all over the place (5V is USB voltage so they are used in a lot of stuff) so he put the green LED in the common leg to raise the voltage between output and common by 2V (5+2=7). If you use the 7V regulator in the first place you don't need the LED.
 

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Discussion Starter · #19 ·
Thanks to everyone for the information and help. I have the bike all put back together and everything running smooth as buttered silk.

Built a new regulator using the original heatsink, some hot glue, an LM7805A and a green 5mm 2.1V LED as suggested in the original regulator tutorial. We don't have anywhere local I could get a 7807 so I usd the original specs. Temp shows normal even after a good hard ride. I am super happy with the results and can't begin to express enough gratitude to all the people who posted on this topic.

Now for the next adventure, how hard is it to replace rear brake shoes lol :)
 

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Do the shoes really need to be replaced or does the brake just need to be adjusted? There is supposed to be a little metal tab on the brake camshaft that lines up with the arrowhead cast into the brake plate when the shoes are worn out. If they don't line up when the brake is applied you should still be able to adjust them.

BTW: Brake shoes on these bikes last nearly forever. The ones on Eccles were used when I got them in 2006 and I have put something like 77,000 Km on it since then. Eccles is a winter driven sidecar machine so I can pretty much guarantee that its back brake gets used at least twice as much as the ones ones most 2 wheelers. A few days ago I adjusted the brake for what will probably be the last time with those pads...
 
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