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gunydgun

Joined:

Jul 09

Posts: 2

gunydgun says:

CB500 Coolant leak

Hi, 

I have a 96 CB500 which has been spitting out coolant from the overflow / expansion chamber - at first when it got hot, but now pretty much whenever it's ridden. 

So far it's been to three mechanics. The first topped up the coolant, and then decided it was a head gasket problem since it was bubbling and overflowing immediately. 

The second said  that the first mechanic had overfilled it, which is why it was spitting out the excess of the coolant, Also he said the thermostat switch was dead and replaced it. After that the fan started to come on once or twice and then didn't anymore. Yet coolant kept overflowing. 

Then the official honda dealership bled the system saying there was an airlock, which meant the coolant didn't reach the thermostat to activate the fan. After that the fan comes on just fine, yet coolant still flows over. After taking it back to them showing them that coolant still gets thrown out (and more of it does when the engine is revved hard), they think it's a head gasket problem as well. 

Some things to note:
1) Bike runs and sounds fine - plenty of power, no backfires, no coughing
2) Coolant is clean (not milky), the oil also is clean.
3) No unusual exhaust smoke.
4) The first mechanic did a compression test - one cylinder has 175psi, the other 125. He felt that was sure proof of a head gasket problem. The second mechanic said with a 13 year old bike you can't expect perfect results and if there was a problem with one cylinder, he would expect performance to suffer (which it doesnt).

What could it be? Head gasket blown, even though the bike doesn't show most of the symptoms?? Since all three mechanics have quoted vastly different amounts for changing the head gasket (ranging from £300 to £1000), I'm now not sure what to do... 

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  • Posted 6 years ago (12 July 2009 14:08)

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

Happening again

Maybe I was little over-optimistic last year thinking that it just needed a coolant change. It started again. It's in for service at the moment. I mentioned to the garage that it might need a new radiator cap. The engineer emailed me later saying it did need a new cap (said it was the seal, but the seal always looked fine to me) and that there was an airlock. He said he's fixed it now so hopefully that'll be the end of it.

[This Reply has been modified by the Author]

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kcmc

Joined:

Jan 08

Posts: 7164

kcmc says:

Strange

Bit weird,you didn't post the first problem anyway and now you reply to not your posting three years later:shock: 

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

Huh?

KCMC,

I'm a bit confused by what you've written. There have been about ten replies to the original post, a couple of which were mine and one of which was yours, dated 12 July 2009.

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

Think I've cracked it!

Following the waste of £30 on a new radiator cap, I've been corresponding with a number of bikers regarding my cooling problem and took the thermostat out today. It was sticking (the internal part was actually sitting at an angle and jammed).

I think that's what caused my problem and would probably explain why it only happened about 50% of the time.

Admittedly, I haven't put a new one in yet, but that must be what caused my bike to spit coolant out. I managed to snap it back into place and got it working OK many times in a saucepan.

I'm not going to risk it though. Sod's Law says it will fail again if I put it back. I'll just get a new one.

Thanks for everyone's help and advice.

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

It was my water pump!

After changing the thermostat, fan switch, having the rad professionally checked...it finally turned out to be the water pump. Deceptive as when I took it apart, it was absolutely sparkling inside. Looked like new. It was still faulty though.

eBay replacements were no good, so I bit the bullet and bought a new one from Honda (yikes!).

Bike has been fine ever since. Problem solved! (Only took me about two years....!) :-D

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