Ford Ka - Over heating - threestar

Hi.....looking for a little advice on a over heating issue on ford ka

Its a 1.3L, 58 plate, no air con.

Car starts, and runs OK, internal heater starts to warm car, radiator and expansion bottle both fill with hot water, electric fan on external radiator works.

Not using any water.......after 20 mins round town driving dash warning light comes on, put internal heating on full (open a window) and after 20 secs or so warning light goes off and stays off as long as you keep heater on.

Warning light comes on if driving motorway speeds, just takes a little longer then goes off again when you put heater on full.

Any ideas please?

Ford Ka - Over heating - elekie&a/c doctor

Is this an old shape (original model) or the current model ka.

Ford Ka - Over heating - threestar

Old shape

Ford Ka - Over heating - elekie&a/c doctor

Is there even heat across the radiator,or are there cold spots?

Ford Ka - Over heating - threestar

feels pretty even.....top maybe hotter than bottom a little

Ford Ka - Over heating - elekie&a/c doctor

My initial thought is that the thermostat is faulty.There is inadequate coolant flow through the rad.Don't think it will be water pump as the heater is working ok.

Ford Ka - Over heating - threestar

OK.........thanks, I'll change that. Do you know if there is anything else worth doing while thermostat is out

Ford Ka - Over heating - dieselnut

" anything else worth doing while thermostat is out "

Flush the rads & engine in both directions until the water runs clean.

Add 50% anti-freeze & bleed all air from the system.