i had my expantion tank replaced and stated to get coolant loss so replaced the cap every thing was fine for a week no loss at all then coolant light came on it was below min ,so have to top up its not over heating can anyone advise please

 

Could be leaking from any place in the coolant system.

When you park it, is there a puddle (or wet spot) underneath the car? Is there coolant on any part of the underbody? Do you have a skid plate you can take off and check?

The first part is to find a leak by finding out what part of the cooling system is above what is wet.

Another possibility is a head gasket leak which would require a compression test.

You probably replaced the thank, filled it up, then it was such a slow leak you thought it was fixed when it was slowly dripping out.

 

Hi yes there is a wet patch underneath the car when I park it's below the coolant tank ,I don't have a skid plate .this problem started when garage replaced the tank after they found a crack in the old tank while doing a service was fine for a week went to use it there was a big wet patch under the car and tank level was below minimum,I replaced the cap with a new one,worked fine went on long journey over 150miles no problem no over heating or any water loss fine for over a week I thought it was fixed then it's started again I've had to top up water every day by a few inches .

 

My guess is something around the tank then. Possibly a torn hose. Check for cracks in the hoses leaded to and from the new tank. Or possibly even the new tank is defective.

 

Checked the tank today lifted it up found leak on the hose coming from the bottom of the thermostat the hose has a slight bulge aswell going to try and get one at the weekend hopefully that will fix it thanks