coolant leak after top-up

[Space]

Yesterday, I added a litre of water in the coolant tank of my Punto, following the advice of someone who is (usually) very competent about car mecanics.
A hundred miles later, the carpets at the front of the car were soaking with some greasy liquid..
According to what I read, it means there could be a leak in the heater.
Why would a top-up create such a leak ? How can it damage anything?

[Waggers]

Hi

This does sound like your heater matrix is leaking. Why did you top up the coolant level? When you added more coolant did you note the level before and after? To be honest you can't really overfill the coolant reservoir - most cars have an overflow tank if there is too much liquid in the system. It might be a simpler problem such as a loose hose. Can you get down there and have a look to make sure all the hoses are connected correctly?

[Space]

I was just told to top it up after someone had a quick look inside the bonnet. I didn't check any level.
I forgot to mention that there was hours of traffic jam and city driving, and the car isn't really used to it. (It seems to really hate London and prefers Somerset)
Also, maybe things would have been different if I put some proper cooler instead of water? there would have been less pressure?...

[Waggers]

Sounds like your car had an adverse reaction to those London roads! Ideally you should use a proper mix of water and coolant but just adding water would not cause the problems you mention. If I were you I'd dry the carpets and check the coolant level again. It may be an isolated problem. If it happens again though it may be time to nip to the garage and get the system checked.

[Eddiecurrent]

The heater matrix leaking was probably the reason you needed to top the coolant up in the first place!