Hi, recently purchased a mk1 focus 53 plate 1.8 mp3 model and the coolant cap keeps coming loose, i filled up the coolant tank yesterday as it was bone dry! and tightened the cap up but if i tighten too much it goes loose again, (is this normal) :S but got it so it was tight checked it just now after driving 3/4 of a mile and its become loose again, i know this can lead to major problems of the engine head gasket blowing or engine possibly seazing? any advice out there?

Sounds like either the cap or the tank has cross threaded. It should do up nice and tight. A replacement cap is cheap. Not so sure about the tank unless you get one from eBay.

Here is a selection of parts:

http://dsa.ebay.co.uk/sch/?&_nkw=Focus expansion tank&clk_rvr_id=537343371479&campid=5337407945&imp_rvr_id=537346055864&toolid=710534811925530&ck=undefined1&mpcr=10982989&ir_DAP_M2=10982989&customid=

Check its the right shape.

You need to get it sorted as the system needs to be pressurised to ensure the coolant circulates properly and doesn't boil. Under pressure the system will maintain a temp of up to 120 degrees or more without boiling. Without pressure it will boil at 100 degrees and as it wont circulate it will overheat.

As above shouldnt be doing that so a cross thread or over tightening

A replacement cap is pretty cheap and definitely worth changing first before looking to the thread on the tank.

Try the cheaper option first.

http://pages.ebay.com/link/?nav=item.view&id=400405552114

Cheers for the advice, think il take it back to the dealership i got it from first, only had the car 2 weeks and this is the 2nd issue already, it comes with 3 months warranty but i expect this problem wont be covered if it leads to worse things (headgasket damaged) then me replacing parts would void the warranty?

As long as the parts used are original Ford your warrsnty is fine.

Defo take it in though, let them pay.

👍 definately will do