Coolant/Radiator Overflow Tank

[Jordan]

Yesterday I took the Pagode out for a drive to meet a friend for lunch.  On my return when I shut off the engine I could here a dripping.  I looked underneath and saw it was coming from the radiator overflow tank.  Opened the hood and sure enough it was dripping from the side spout next to the rad cap.  I let the engine get cold and removed the rad cap.  The coolant was right to the top of the tank.  Nothing floating on the surface, no colour change that I could see, very clear fluid.  I took about 500ml out to get it back to the tab inside the tank.

I have been driving the car all summer and have never added coolant and have never had it overflow like this.  What would cause this?  The engine temp was 80C when I parked it so no over heating.  It was very cool when I drove it, around 10C (50F) and I already had the heater core levers open so I could get heat at my feet.   I did hear a funny noise coming from the front when I was driving the car back from lunch but it went away.

So where would the extra coolant come from to cause it overflow?  What should I be looking for or testing?  I don't really know where to start with this.  Appreciate any insights.  Thanks.

[Jordan]

I should mention after thinking more about the noise I heard, it sounded like the noise a playing card makes when someone clips it to their bike wheel, but muted.  I was thinking the fan but the noise would go away when I came to a stop so that would suggest neither the fan or engine.

[Jack the Knife]

Could you post a picture of the cap on that overflow tank, if you don't mind?

[Jordan]

Could you post a picture of the cap on that overflow tank, if you don't mind?

See attached.  I've had the rad cap on their for years.  Could it be a faulty thermostat?

[Jack the Knife]

See attached.  I've had the rad cap on their for years.  Could it be a faulty thermostat?

I asked since sometimes the wrong cap makes it on there over the years that is rated for a different pressure. Hmm.. I wouldn't even call myself a shadetree, so take this with a grain of salt, but I would surely look at the thermostat as well as ensure there aren't any clogs in any of the coolant return lines or the radiator.

[Cees Klumper]

I thought expanded coolant would go into the overflow tank, not onto the street? Not near my car so can't double check the system right now - but maybe check that the passage to the actual overflow tank is clear and coolant can go there, as opposed to escape to the street. And perhaps try a new radiator cap, maybe the current one started to leak.

The sound you heard was likely the exhaust cooling off.

[Jordan]

I thought expanded coolant would go into the overflow tank, not onto the street? Not near my car so can't double check the system right now - but maybe check that the passage to the actual overflow tank is clear and coolant can go there, as opposed to escape to the street. And perhaps try a new radiator cap, maybe the current one started to leak.

The sound you heard was likely the exhaust cooling off.

Thanks Cees.  The sound I heard was while I was driving.  I heard if for a few minutes, faster when I went faster and slower when I went slower and nothing when I was stopped, before it stopped completely.  Don't know if its even associated.

The over flow tank has a drain spout.  If the pressure exceeds the radiator cap pressure rating the spring loaded cap opens up and allows coolant to flow into this drain spout, to relieve the rad pressure.  Not sure how the pressure could climb so high in the overflow tank if the passage to the tank was blocked.  The coolant was definitely dripping from this spout, not from the rad cap.

[Cees Klumper]

Ah, right. Perhaps the cap has failed and is no longer able to maintain the proper pressure on the system.

The sound may have been 'something' stuck between the (inside of the) wheel / brake disc/pads etc, like a small twig or leaf.

I would still try putting on a new radiator cap and see if the issue comes back. It sure sounds odd, given that the car was not overheating and it was in any event cooler than during the Summer when you were also using the car.

[rwmastel]

The over flow tank has a drain spout.

It should have a hose going towards the ground.

[Jordan]

So took it for a short drive today to see what would happen.  I know the thermostat is working because I see the temp gauge climb just above 80 before it drops back down to peg at 80C.  No noises.  Heat at my feet.  Got home and nothing coming from the over flow tank.  Used a temperature gun and couldn't find any cold spots.  Rad was hotter across the top and cooler across the bottom and all coolant hoses hot.  Let the car cool and opened the rad cap and the level was just a titch below the tab inside the over flow tank.  All seems normal now, just scratching my head.

Question, I've read that some recommend changing the rad caps about every 5+ years.  Do others do this?  I'm wondering if the spring in the rad cap has maybe lost some of its strength and is no longer suppling 1 atm of pressure.