Replaced the thermostat with my local garage which took 2 hours. No problem there. However we replaced the anti freeze to the correct level and the low coolant warning light comes on. I know there is a plunger mechanism that sometimes goes wrong which means a new expanision tank costs $$$ . I found the connecter that leads into the tank which is connected to a plastic stick. Removed this and no more light ! I think I will put some more miles on the car before re inserting the connector stick to see if the expansion tank plunger has decided to start working again.

If not is there a part I can replace in the tank without buying a new one. I am half tempted to just leave it out. I have the water temp guage to tell me whats going on.

 

I would suggest replacing the bottle. Sometimes it's the bottle thats bad inside, and sometimes it's the sensor. Better to take out both that way you don't have issues later.

 

Thing is the expansion tank was fine until we added some new antifreeze and water (Correct amounts). Build quality of these cars is terrible.