What is this?!

[Tom__40]

Hi. My 2000 Polo Mk3 1.4 (~88000 miles) seems to have developed a slow coolant leak. At least I think it's a leak, maybe an airlock after not putting the cap on the expansion tank or something? I've had a good poke around, hoses all seem ok. I did come across a push fit plastic cap of some kind, could easily have been knocked working on other bits. I've pushed it back in, but I've no idea what it is and if it's related to the coolant system?! In the second photo you can see the ends of the radiator hoses connected to what I presume is a pump of some kind. The white flecks on the metalwork near the plastic cap I think are dried coolant, there's some more further down/underneath (pink deposits, so pretty sure it's coolant.

Currently topped up and marked the line with a pencil, I'm hoping it won't have emptied by morning!

cheers

 

[Burnerman]

Its a timing mark bung.....just keeps crap out of the flywheel /clutch area.
Don’t pour anything in there!
John

 

[Tom__40]

Great, thanks. At least I know it's not that now!

 

[Burnerman]

The thermostat housing - plastic- is prone to fracture on these so keep an eye out where the hoses enter the housing.
John

 

[Tom__40]

...after looking and looking I think I've found it. Don't know why I didn't check this earlier, but I reckon the radiator itself is leaking. Pink deposits at the bottom either end of it, and on the plastic thing underneath (drip tray?) there's a puddle of pink coolant at one end. It's damp with it all the way along though. Quick look in the Haynes and I reckon I can change it myself (need more coolant now though), and radiator appears to be only £25-30 on ebay, not too bad

 

[Burnerman]

Yep, that’s where they go, where the vertical vanes connect to the bottom tank.
Easy enough to change, be very careful with the new one as they are fragile.
You’ll have to remount the cooling fan, and it could be a good move to replace those horrible spring hose clamps with jubilee type.
Replace the coolant with a 50% antifreeze mix.
John