Honda CX 500 Forum banner
1 - 20 of 153 Posts

·
Registered
1979 CX500 Custom, 1981 GL500 SilverWing
Joined
·
92 Posts
Discussion Starter · #1 ·
My '79 CX500 Custom's heat gauge is just a hair below the redline while riding around the city. At highway speeds, it reads just a hair above midway. I had removed the radiator and looked at the fan and to me it looked brand new but I wonder if there's a way to check if it's actually turning. Five or so minutes after cold-starting, the left-side coolant pipe heats up so I'm sure the thermostat is okay. My '81 GL500 reaches midway and stays there, no matter where I'm riding...
 

·
Super Moderator
Joined
·
5,681 Posts
The fan is turned by the camshaft. The only way for the fan to not be turning is if it has come loose on the end of the camshaft. This is unlikely and if it were the case I would expect unusual noises from that area. Easy to check if you still have the rad off, just try turning the fan. It shouldn't.
It could also be a problem with the temperature gauge and/or the 7 volt regulator or more likely a radiator that needs a good cleaning and flushing.
 
  • Like
Reactions: Del and washoe

·
Registered
1982 CX500C
Joined
·
97 Posts
Thanks, Relic - do you think I should take the radiator to a radiator shop ?
Drain the radiator into a clean container - if the coolant is brownish in color and/or has sludge or heavy contamination, take it to be cleaned and flush the block as well.

You could also take it to a radiator shop for your own peace of mind. Besides cleaning it, they can check it for leaks and potentially repair it (if possible).

Either way, make sure to test the pressure cap as part of your diagnosis. This is something easily overlooked and faulty pressure caps can allow the coolant to boil if the temp gets hot enough.

Any auto parts store that rents tools should have a tester, but one quick test is to get the engine up to operating temp and shut it down. After 30-60 seconds, try squeezing one of the coolant hoses - it should be firm with little give.
 

·
Registered
1982 cx500tc turbo
Joined
·
164 Posts
Hi
At least we do have a couple rad shops in Edmonton

Norwest cooling systems South Edmonton ..Old shop been around for a long time

Hunter radiator Southe side Edmonton been around for a long time

West end Radiator Edmonton not sure what the do in house

Stay a way from the muffler and rad shops in Edmonton all they do is send it to a Radiator shop to have it done :mad:

TLD 🇨🇦 🇩🇰
 
  • Like
Reactions: washoe

·
Registered
Joined
·
2,639 Posts
Definitely check the 7 volt reg output before you do anything more involved. It’s a fairly common failure point, and cheap/easy to replace.
 
  • Like
Reactions: Del and washoe

·
Registered
1979 CX500 Custom, 1981 GL500 SilverWing
Joined
·
92 Posts
Discussion Starter · #8 ·
Thanks, Relic, Gumby, Doug, Dane and Rich - UPDATE: I went for a fifty-mile ride, all well until back in town, steam coming from underneath somewhere, coolant flowing out of a small hose, coolant inside the reservoir boiling !... waited an hour then a 5-minute ride home. I think I have a meter, if I turn it to "20", it seems to tell me the charge on the car battery, I'll see if I can find the voltage regulator - I have the FSM downloaded... thanks again, everyone.
 

·
Super Moderator
Joined
·
5,681 Posts
I believe that the 7 volt regulator is in the area of the instrument cluster. It has green, black and yellow wires. Black is 12 volts in, yellow 7 volts out, green is a ground.

Another possibility not yet mentioned is the water pump. Any strange noises from the water pump area at the back of the engine?
 
  • Like
Reactions: washoe

·
Registered
1979 CX500 Custom, 1981 GL500 SilverWing
Joined
·
92 Posts
Discussion Starter · #14 ·
I believe that the 7 volt regulator is in the area of the instrument cluster. It has green, black and yellow wires. Black is 12 volts in, yellow 7 volts out, green is a ground.

Another possibility not yet mentioned is the water pump. Any strange noises from the water pump area at the back of the engine?
Thanks, Relic, I have an "AstroAI AM33D" with pointed ends - if I stick one into the yellow and one into the ground, it should read 7 volts ?
 

·
Registered
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
Joined
·
12,099 Posts
... coolant flowing out of a small hose, coolant inside the reservoir boiling !....
Sounds like a head gasket leak.
Set each cylinder at TDC compression, pressurize it, and watch the reservoir.
 
  • Like
Reactions: D-Fresh

·
Registered
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
Joined
·
12,099 Posts
I attach my compressor to the adapter I made for my compression gauge.
In lieu of that, some air nozzles have a blunt rubber tip. With a short extension, it would seal against the spark plug hole.
 

·
Registered
1979 CX500 Custom, 1981 GL500 SilverWing
Joined
·
92 Posts
Discussion Starter · #19 ·
I attach my compressor to the adapter I made for my compression gauge.
In lieu of that, some air nozzles have a blunt rubber tip. With a short extension, it would seal against the spark plug hole.
Yes - good idea, Randall... there are two TDCs, compression and exhaust, yes ?... and nothing should happen in the reservoir or anywhere else for that matter - the engine should be sealed ?... I might have to go to an automotive supply place and see if they have a tip for the compressor that matches the bore of a spark plug... between all these suggestions, I have a full day's work ahead of me tomorrow, starting with removing the seat and tank, I guess !... Thanks again, everybody, I'll try to troubleshoot the cause of the boiling over and spilling out onto the street through that small tube that I think came from the reservoir...
 

·
Registered
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
Joined
·
12,099 Posts
Yes. On compression, all the valves will be closed (the pushrods should rotate easily.) Having the valve covers off will provide easier reach to the plug holes, too, so plan to remove them.
Any bubbles appearing in the reservoir will indicate a leak at the fire ring between the combustion chamber and coolant jacket around the cylinder. It will identify which cylinder is at fault, too.
 
1 - 20 of 153 Posts
Top