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1978 Honda CX500
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Discussion Starter · #1 ·
Hi All -

I'm a new member here and a new motorcycle owner in general. I picked up a 1978 CX500 a couple weeks ago and have been learning to ride!

I got back from a lunchtime ride yesterday and I noticed what appeared to be a leak from one of the tubes connected to the crankshaft breather (thankful to this forum for the PDF of the owner's manual so I could identify this.) I think it's leaking coolant based on the color of the fluid coming from the tube but I'm honestly not sure.

I haven't noticed this before when I've gotten home from rides, is this something I should be super concerned about? And is this a doable fix/project for a brand new motorcycle owner? Video below, which was taken after the majority the liquid had leaked at out. All told I'd say a couple ounces had leaked out at more of a trickle than the drip in the video.

IMG 1180

Any tips or advice would be great appreciated!
 

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Premium Member
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,452 Posts
Is that the coolant reservoir overflow, or one of the two airbox drains? (Those two should be plugged.)
Check the coolant level in the reservoir bottle when it's dripping (presumably warm.) Is it up at the top, vs half full when the engine is cold?
 

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'84 CX650E that is evolving into a GL500
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18,924 Posts
I think you mean crankcase breather, not "crankshaft breather". Your video shows the two breather drain hoses with their caps (those caps should be pulled periodically to allow the condensate to drain from them and then replaced) and a 3rd hose, which is dripping.
I'm not familiar enough with the CX500 to say where that hose comes from but I'm sure it has nothing to do with the breather system. My first thought was that it could be the battery's vent tube but if what came out of it is the same colour as the stuff in your coolant recovery tank (what Randall called "reservoir bottle" - located between the back of the engine and the front of the swingarm) it is probably the tank's overflow hose.
If you aren't sure of the colour of the liquid catch a few drops on a piece of white facial tissue or toilet paper (it is a good idea to have a roll of toilet paper in the shop for when you need something clean & disposable to wipe something with).

I would not recommend riding the bike again until you find out exactly what is going on and why this is happening. It could be as simple as an over filled recovery tank (the level should be halfway between the lines when the engine is cold) but it could also indicate a blown head gasket.
As well as checking the level in the recovery tank have a look at the dipstick and tell us what the oil looks like (again, dripping some onto white tissue makes it easier to see). Is it transparent amber or does it look like chocolate milk? Milky oil indicates that water (or more likely coolant) has become mixed with it so DO NOT run the engine until the problem has been fixed and the oil replaced.
 

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1978 Honda CX500
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8 Posts
Discussion Starter · #4 · (Edited)
Is that the coolant reservoir overflow, or one of the two airbox drains? (Those two should be plugged.)
Check the coolant level in the reservoir bottle when it's dripping (presumably warm.) Is it up at the top, vs half full when the engine is cold?
The liquid coming out of the hose looked a clear yellowish, the same color as the coolant. I did notice the coolant level was at top of the container yesterday when I finished my ride so this sounds like the root of it? And that I just put too much coolant in, and the overflow tube was doing it's job? Also, thanks so much for troubleshooting this with me! Being very new to motorcycles, I really appreciate it!
 

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1978 Honda CX500
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8 Posts
Discussion Starter · #5 ·
I think you mean crankcase breather, not "crankshaft breather". Your video shows the two breather drain hoses with their caps (those caps should be pulled periodically to allow the condensate to drain from them and then replaced) and a 3rd hose, which is dripping.
I'm not familiar enough with the CX500 to say where that hose comes from but I'm sure it has nothing to do with the breather system. My first thought was that it could be the battery's vent tube but if what came out of it is the same colour as the stuff in your coolant recovery tank (what Randall called "reservoir bottle" - located between the back of the engine and the front of the swingarm) it is probably the tank's overflow hose.
If you aren't sure of the colour of the liquid catch a few drops on a piece of white facial tissue or toilet paper (it is a good idea to have a roll of toilet paper in the shop for when you need something clean & disposable to wipe something with).

I would not recommend riding the bike again until you find out exactly what is going on and why this is happening. It could be as simple as an over filled recovery tank (the level should be halfway between the lines when the engine is cold) but it could also indicate a blown head gasket.
As well as checking the level in the recovery tank have a look at the dipstick and tell us what the oil looks like (again, dripping some onto white tissue makes it easier to see). Is it transparent amber or does it look like chocolate milk? Milky oil indicates that water (or more likely coolant) has become mixed with it so DO NOT run the engine until the problem has been fixed and the oil replaced.
I just checked the oil, it's a clear amber color. No milky coloration whatsoever which is good. The liquid that was leaking out of the tube was a clear yellowish, making me think it was the coolant and this tube is the overflow hose. Forgive the obvious question, but as I'm new to all of this, I'm assuming that the root of the issue here is that I just filled up the coolant too much and the overflow was just doing it's job? Also thanks so much for such an in-depth answer, I really appreciate it!
 

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Premium Member
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,452 Posts
If you're lucky, it's just overfilled.
Run the bike up to temp and watch for bubbles in the reservoir. That will indicate a head gasket leak. If you have access to a leakdown test rig, or a compression test adapter that will connect to a compressor, you can do a similar test without running the engine. The latter will also help you determine which cylinder is leaking.
It's too bad you aren't closer. You might be looking at a crash course in motorcycle mechanics.
 
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