I'm an American living in Ireland and have a question I hope someone can shed some light on.

I have a 1.1 litre Mistubishi Colt, has been great car, over 150k miles no trouble. Recently I was doing a small service on the vehicle myself. Changed oil, coolant and plugs. When I was tightening in one of the plugs I went a little hard and heard a light 'click' sound.

Immediately, thinking I've cracked the head, I began to panic and watched the coolant reservoir religiously over the next month.

In normal day to day driving noticed no coolant was being lost. This was over about 100 miles a week with city driving.

A week ago had to drive high rev's(3,500RPM) for 400 miles to a wedding and back, and lost about 100 - 150ml (5 ounces) of coolant. I know it is a very small amount but I am anxious to find out if there is anyway I can stop / repair the damage I may have caused. The car is not worth much and if it lasted me another year I would be happy. I realise I shouldn't have changed the plugs without a torque wrench but am hoping that there may be a way to fix this.

Any ideas? Thanks for your help.