hello new member here looking for some assitance regarding coolant loss and bubbles from overflow on my focus, issue started around 3 weeks ago , after doing some research ive replaced thermostat housing which seemed to have coolant residue and problem continued so i ive tried to find the leak myself by visual inspection and checking pipes and overflow tank and fan/heater components and everything seems ok according to online information but unsure on expansion tank as there is a wet patch beneath it but the tank itself is dry, coolant seems to go down below min when hot and stay there with air bubbles but once cooled down and started again after thermostat opens coolant goes back to max , takes a while for bubbles to start showing once hot also not immediate, im just wondering if anyone has any ideas what it could be or anything/anywhere else i could possibly check for a coolant leak, i understand it could be head gasket so ive ordered the dye test that goes over expansion tank, car is going to garage next week anyway but id love a go at trying to find the leak myself, hope someone has suggestions will keep updated with what the problem was when sorted, many thanks

Hello Welshie, welcome.

It sounds like you've already done or are doing all the right things to understand the problem. What engine do you have in your Focus?

Ref wetness under the the expansion tank, they have been known to crack but that probably wouldn't explain the bubbling and varying coolant levels.

Have you noticed any significant increase in white vapour from the exhaust? Not easy to assess at this time of the year with the colder weather.

Check that the carpeting isn't wet in the footwell. Pipe seals at the heater matrix are known to leak.

2 minutes ago, RayC333 said:

Hello Welshie, welcome.

It sounds like you've already done or are doing all the right things to understand the problem. What engine do you have in your Focus?

Ref wetness under the the expansion tank, they have been known to crack but that probably wouldn't explain the bubbling and varying coolant levels.

Have you noticed any significant increase in white vapour from the exhaust? Not easy to assess at this time of the year with the colder weather.

Check that the carpeting isn't wet in the footwell. Pipe seals at the heater matrix are known to leak.

Hello ray many thanks for the reply

i did forget to mention that i had checked for white vapour and in all honesty theres hardly any after initial warm up, car is running sweet.

ive not checked the carpeting so ill deffo do that tomorrow, and if it is wet is that hard evidence the heater matrix is causing fluctuation and air bubbles? will google that now also.

many thanks for taking the time to help

Just an update as to footwells and under dash no wetness or stains, anymore suggestions? thanks

Coolant tank cracked or expansion cap spring failed if there's still a wet patch under the tank when running.

 

12 minutes ago, TomsFocus said:

Coolant tank cracked or expansion cap spring failed if there's still a wet patch under the tank when running.

 

Hello many thanks for the reply

with regards to a cracked tank or failed expansion cap, would that cause air bubbles to come out of overflow pipe or would it just cause coolant loss

many thanks

And engine is a 1.6 tdci, incase there are very common coolant loss problems related to said engine

thanks

13 hours ago, Welshie8 said:

Hello many thanks for the reply

with regards to a cracked tank or failed expansion cap, would that cause air bubbles to come out of overflow pipe or would it just cause coolant loss

many thanks

When pressure isn't held in the tank, air will expand into it in the form of bubbles.  If the water level drops below minimum in use, that can suck air into the system.

However, having read your first post again, it sounds more like you've got an airlock than a leak.  Coolant can't be compressed, so the only way it can disappear and then refill itself is by occupying space that was previously filled with air.  I think it just needs a thorough bleed.

1.6 TDCI takes ages to warm up so they can be a pain to bleed.  They are meant to be vacuum bled at the factory but that's not easy to do at home.

For the wet patch, I would use a bit of white tissue or powder to confirm what colour that is.  It may not be coolant.