Honda CX 500 Forum banner
1 - 15 of 15 Posts

·
Registered
Joined
·
967 Posts
Discussion Starter · #1 ·
So I have flushed the system thoroughly, added sufficient 50/50 mix, built the Green LED "REG"ulator, measured the green/blue lead and am getting a solid 6.99V with the iginition on, All contacts are shiny clean,...the guage is nearly unresponsive.



The Thermostat housing and the cylinder feed pipes are both HOT...so hot I can't keep my fingers on them...maybe 175?F I may borrow a infrared thermometer from my Uncle, but what do you guys think?



I am guessing a couple things are going on...

I would think the sender is going bad or working intermittantly, AND the thermostat is not opening...



How long should it take for the gauge to settle into its normal temp?
 

·
Registered
Joined
·
8,422 Posts
You should run the engine up to running temp with the tank pulled back and the rad cap off to check that the coolant flows when the thermostat opens.This also bleeds the air out of the system which is a requirement.



If the bike is being started from cold and depending on the ambient temps of the day it can take quite a while for engine to get up to running temp as it's not under load.You can speed this up by holding the revs at say 3,000 rpm.



From cold the coolant transfer pipe at the side of the engine will change from cold to hot when the thermostat opens and the coolant starts to flow around the Radiator.
 

·
Registered
Joined
·
343 Posts
My 1980 CX500D takes a while to get to the middle of the gauge. I flushed the radistor , new thermostat, and hoses. The PO had removed the thermostat, so it had no TS when I bought it. It was getting hot when I first got it with no T/S, so I put a new one in. You may need a new T/S also. AGB-1
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #4 ·
Thanks guys. Just not familiar with the bike yet as I've been doing a lot of backed-up/neglected Preventive Maintenance, routine stuff that never got done etc. Change a lot of stuff at once, and sometimes you dont know where you stand.



I will leave the cap off, wait a bit for her to warm up. I know the temp gauge works, as it seemed to heat up a lot faster after I got the REGulator built, but that was prior to flushing the coolant system. Now with the radiator in tip-top shape, it makes sense now that it takes so long to warm up! lots of natural flow in the radiator, and no crud to retain heat!



well, I went back out and let her warm up for about 15 to 20 minutes...the gauge moved, but never past the first block and never came close to the sweet-spot or the middle section. The thermostat did finally open, lower pipe got warm, and I could see the coolant moving, so I know the thermostat is at least responding.



Maybe the sender is needing replacment? They are easy enough to change. Not sure what they cost, but I hate to just throw money at a guess.



Is there anyway to check the sender electrically? maybe someone could go into detail about how they work? I would guess as the resistance changes the voltage to the gauge responds accordingly.
 

·
Registered
Joined
·
309 Posts
Is there anyway to check the sender electrically? maybe someone could go into detail about how they work? I would guess as the resistance changes the voltage to the gauge responds accordingly.


Basically, yep - they`re a NTC resistor, as the temp goes up, the resistance goes down allowing more current to flow through the bi-mettalic strip in the gauge heating it up more, bending it more, which moves the needle.



You can do resistance checks on the sender, though it may be simpler just to test the rest of the circuit first:



Pull the gree/blue from the sender and short it directly to a good earth point.

With the ignition on the needle should sweep swiftly across the gauge.

Keep the wire earthed for as long as it takes the needle to near the red zone.

Test completed!



You`ve already measured 7V at the green/blue so that`s OK, if the needle is still unresponsive after this test it`s the gauge that`s at fault.

If the needle does sweep over then it points to the sender - they`re usually reliable though.
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #6 ·
Basically, yep - they`re a NTC resistor, as the temp goes up, the resistance goes down allowing more current to flow through the bi-mettalic strip in the gauge heating it up more, bending it more, which moves the needle.



You can do resistance checks on the sender, though it may be simpler just to test the rest of the circuit first:



Pull the gree/blue from the sender and short it directly to a good earth point.

With the ignition on the needle should sweep swiftly across the gauge.

Keep the wire earthed for as long as it takes the needle to near the red zone.

Test completed!



You`ve already measured 7V at the green/blue so that`s OK, if the needle is still unresponsive after this test it`s the gauge that`s at fault.

If the needle does sweep over then it points to the sender - they`re usually reliable though.


Fabulous...will check that. So given all of the other things that checkout 'good' should the gauge when grounded sweep to the extreme, can I call the sender the culprit and replace it? They are 30 or so bucks!! I love your ride...I think of Johnny Cash's "one piece at a time" when I see it. its like a recumbant--AWESOME.
 

·
Registered
Joined
·
8,422 Posts
When I did one of Reg's cheap 7v Regulators I found the green ground wire inside my headlight nacelle was not doing a good job so I soldered on another one to it to a good ground point through the back of the headlight and onto one of the bolts on my forks at the top,the little 10mm M6 ones with one of those round end connectors I got from the car shop.



Like you get in these kits,



http://cgi.ebay.com/GARDNER-BENDER-...016?pt=LH_DefaultDomain_0&hash=item1c15fff818
 

·
Registered
Joined
·
108 Posts
Just did mine yesterday, replaced the 31yr old thermostat with another 82deg celcius unit, it only opens from 82deg celcuise the way I understand, went for a 100km trip with the wife & then used an infra red thermo gun to measure the housing, 86deg celcius so I was happy.
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #9 ·
Just did mine yesterday, replaced the 31yr old thermostat with another 82deg celcius unit, it only opens from 82deg celcuise the way I understand, went for a 100km trip with the wife & then used an infra red thermo gun to measure the housing, 86deg celcius so I was happy.


I went out and sent the green/blue to ground, and the gauge very steadily climbed up to Max Temp...so I have verified my gauge is performing nicely--Thanks Eurovee...



Just to confirm you replaced the Thermostat & not the Sender? What were the symptoms of your old thermostat...did you find the bike to be overheating becuase it was not opening? I think my thermostat is working but the Sender may be not performing well anymore.
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #10 ·
When I did one of Reg's cheap 7v Regulators I found the green ground wire inside my headlight nacelle was not doing a good job so I soldered on another one to it to a good ground point through the back of the headlight and onto one of the bolts on my forks at the top,the little 10mm M6 ones with one of those round end connectors I got from the car shop.



Like you get in these kits,



http://cgi.ebay.com/GARDNER-BENDER-...016?pt=LH_DefaultDomain_0&hash=item1c15fff818


Shep, I will certainly investigate the ground issue. It is possible that I may have lost the ground to the sender since everyone seems to believe them very reliable. Now that I have proved the gauge to work well, I will check its ground path.



Ahhh,...the gremlins of a 32 year old beasty! Will follow up later tonight!
 

·
Registered
Joined
·
1,366 Posts
I think the ground for the reg goes back to a chassis connection. Not sure why they even grounded the nacelle.

The sender grounds through the thermostat housing. I guess if the threads are corroded it could be a problem.
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #12 ·
The sender grounds through the thermostat housing. I guess if the threads are corroded it could be a problem.


So I am out there staring at it, and "grounds through the thermostat housing" kept going through my mind...I know the threads are clean...just replaced the O-rings...now pause, and ask yourself, devoid of the mounting bracket that holds up the thermostat housing, what else is holding the housing in place? 2 rubber O-rings, and an Upper Radiator Hose,...perfectly suitable insulators Isolating the Sender from the ground path!!



I left the bracket off so I could check for leaks, and never thought about it being the ground path.







So reinstalled the clean bracket, and the gauge came to life after 5 minutes. Here are three pics...5 Minutes, 12 minutes, and then after the thermostat opened.







THANKS Boulder, and everyone else that contributed!



This certainly brings to light another item to check for when troubleshooting the Infamous "My Temp Gauge" is not working properly. My bracket as well as the bolts that were holding the bracket were corroded pretty heavily, white oxides, and rust--cleaned and secured, and a guage that works!
 

·
Registered
Joined
·
108 Posts
I went out and sent the green/blue to ground, and the gauge very steadily climbed up to Max Temp...so I have verified my gauge is performing nicely--Thanks Eurovee...



Just to confirm you replaced the Thermostat & not the Sender? What were the symptoms of your old thermostat...did you find the bike to be overheating becuase it was not opening? I think my thermostat is working but the Sender may be not performing well anymore.




Reading up, after 31yrs I did not bother testing the thermostat,just replaced it, dirt cheap as it's a common unit. They don't last forever and I did notice an immediate change, bike ran cooler so I can only assume that it was no longer opening properly...



I am still going to again bleed the system just to be sure it is good....also after a rebuild I expect the bike to run a bit hotter till everything losens up,just a thought I had. Push comes to shove, I'll use Engine Ice, same stuff we use on the KTM300 and it works very well...Those 2T cook easily when you in the mountains climbing...
 

·
Registered
Joined
·
967 Posts
Discussion Starter · #15 ·
Thanks for the follow-up Trev
I may replace the thermostat, but for now I know it opens up, and it is opening in a repeatable/predictable spot on the temperature gauge!!
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top