Coolant leaking from radiator cap

[Sstevee]

Hey all,

Just after some advice on a intermittent coolant leak.

The other day I went to betws-y-coed on a ride and when I parked up I noticed coolant leaking from the radiator cap.

The bike temp was fine during the ride but I didn't pay any attention to it during the last 10 minutes when I was slow moving/stationary looking to park.

I got back on the bike to go home 40 miles away and stopped a
Few miles from home to check the situation. Nothing had leaked at this point.

I went the last few miles home relatively slow through town riding and when I stopped the coolant was leaking from the cap again.

The problem seems to happen when I have been slow riding or stationary.

I have done a quick bit of searching online but would like further advice. I don't think it's head gasket as the coolant is still vibrant green in colour and the oil looks normal.

Any tips or pointers would be great

[andys675]

buy a new cap?

they don't last forever, it may just be beyond it's useful lifespan

you don't say how old your bike is or how many miles it has done
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Some people feel the rain, others just get wet.

[Sstevee]

Sorry how stupid of me

Honda cbr600rr 2004 21,000 miles

Think the cap is my first thing to try

[Pjay]

If it's not overheating, it's just the cap.

[Pete.]

Even if it is overheating the cap is designed to allow coolant to bypass directly into the expansion tank, then return to the system once the engine cools down. If it's leaking at the cap then the seal has failed. This will have two important effects:

It will reduce the level of coolant in the system and introduce air.

If the pressure cap is not holding the system up to pressure it will allow the coolant to boil at a lower temperature than normal, because the usual 11-15psi (or whatever pressure your cap holds) actually elevates the boiling temperature.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[bladerunner]

As above really! check the cap visually around the seal just in case its a bit of debris or new cap time. If I remember right the hondas rad fan kicks in at 105'C and with no pressure in the system water will boil at 100 so you'll be venting coolant even before the fan kicks in. with the system holding pressure water wont boil until around 120'C. if the bike hasnt had coolant changes every couple of years it can build up with oxide and thats the kind of debris id expect to see on the seal
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's