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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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steve.g

Joined:

Jan 08

Posts: 5770

steve.g says:

is yer water pump..

playing up? cap on tight? i would expect milky oil with head gasket....but would depend where head gasket blowing if so. go to independant bike shop....the prices you have been quoted (if head gasket gone) are ridiculous. there is potential of a kink in a water line / blockage also. is your oil filler cap clean oil? i suspect, if it is, there may be simpler prob like the pump. the coolant has to run under pressure, if there is a cap leak, the water will boil earlier i believe. strange prob....

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steve.g

Joined:

Jan 08

Posts: 5770

steve.g says:

by the way...

does yer exhaust steam at all after few mins...or when hot??

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jaffa90

Joined:

Mar 09

Posts: 8817

jaffa90 says:

leak

I would say head joint (gasket if there),if you could pressurise the cooling system it probably would fill a cyl with coolant.:unsure:

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kcmc

Joined:

Jan 08

Posts: 7164

kcmc says:

Before

spending your hard earned on a head gasket replacement.Just try replacing the filler cap,it is quite common on a bike of this age for the spring in the cap to become weak.If the cap is say 1.5bar and the pressure in the system is 1bar,if the cap spring becomes to weak,say .8bar then it will blow out of the header tank.The cap can be tested(quite surprised your mechanics haven't check this first)If you follow the top hose off the radiator under the tank you will find your filler cap and housing which is attached to the thermostat and its housing.Still could be a head gasket blowing,but could be a lot cheaper if its just a cap!!

Good Luck

K.C.:tongue:

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gunydgun

Joined:

Jul 09

Posts: 2

gunydgun says:

Actually....

nevermind about performance not suffering.... The other day it started to struggle, revs fell to about half of what they should be and there was a nasty knocking sound. Then it just gave up and wouldnt start anymore. So I guess now there's more to worry about than just a cap or gasket or whatever... It's going back to the local mechanic and he can have another look to find out what the extent of the damage is... :upset:

Still there was absolutely no smoke (not even when hot), and no mixed fluids.

Thanks for all your inputs anyway!

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steve.g

Joined:

Jan 08

Posts: 5770

steve.g says:

if yer engine knackered...

get one from breaker few hundred quid. dont pay mechanic rates to rebuild yer engine.

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

CB500 Coolant leak

I know this is an old thread now, but I'm posting this for the benefit of anyone else who's had a similar problem.

I recently purchased a '98 Honda CB500 from a friend. He mentioned its only fault was when it got hot (sitting in traffic) the fan often failed to kick in and it leaked coolant. (He would just switch the bike off until the traffic started to move).

He'd had the fan switch replaced on a mechanic's recommendation but no luck. After some googling, I found this thread and suspected the cap. Local Honda dealer said the spring felt a LITTLE loose but rarely ever had to sell any replacements. It certainly felt fine when it was fitted and I couldn't find ANYWHERE that could test it for me, so I didn't bother with a new one just yet. (£25!)

Another forum suggested doing a full coolant flush, which seemed to me to be the most sensible first course of action on a newly-acquired bike. (It did recommend using Honda's own coolant, which although more expensive I decide to try). Think I spent about £20 in total.

I'm new to biking so armed with my new Haynes Manual, I followed the procedure to the letter. The 'old' coolant was very clear and clean-looking so I didn't think that would be the problem.

I inadvertently put SLIGHTLY too much coolant in and so once I'd restarted, it spat some out again. Once the excess was expelled and it had found its level, it ran fine. Fan kicks in EVERY time at about half temperature and cools efficiently. It no longer spits out coolant.

I suspect it may have been the above-mentioned air lock (although wouldn't that have been addressed when the fan switch was replaced?).

Not sure if it just had the 'wrong' type of coolant, but the fan and coolant have been fine ever since I did the coolant change.

[This Reply has been modified by the Author]

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smidget

Joined:

Nov 07

Posts: 2407

smidget says:

Hi

you state that the coolant you removed was clear this indicates no anti-freeze therefore the boiling point would be lower.

It is always best to leave the expansion tank top off and warm the bike up, I would run mine until the fan has cut in and then replace the expansion tank cap.
This allows any trapped air in the system is expelled.

It is always best to use anti-freeze with inhibitor and mix it 50 / 50 with water, there is a product on the market called 'water wetter' which assists cooling further.

[This Reply has been modified by the Author]

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magicmanalex

Joined:

Oct 10

Posts: 6

magicmanalex says:

My bad!

Thanks for the 'warming-up' tip - I'll bear that in mind!

I should apologise though - when I said 'clear' I should have said 'transparent'. The point I was trying to make is that it was clean, instead of milky or dirty.

It wasn't clear - it was blue in colour. It just looked very clean and fresh and didn't look in any way contaminated.

I replaced it with Honda ready-mix coolant, straight out of the bottle.

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smidget

Joined:

Nov 07

Posts: 2407

smidget says:

magicmanalex

no problem, just hope the info helped.

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