These engines are not common for head gasket issues. I would take a close look at the plastic thermostat housing which is located behind the Aircon pump. Difficult to see from above . These very commonly fracture and leak . If the expansion tank is half full , but still overheating, then I suspect there is an airlock in the coolant system . These can be difficult to bleed correctly.
An airlock shouldn't lead to consistent coolant loss though if its in the process of clearing itself escaping air may cause blow-off from the coolant reservoir. An air lock can thus do a fairly good impersonation of more serious head gasket failure.
I had these symptoms on the Skywing which everybody and his dog assured me was a head gasket failure; which are apparently quite common on these 3-cylinder engines, especially when turbo-boosted.
Cleared itself eventually
These days if I drain the system I clear airlocks by boiling the coolant with the radiator cap off and the fan disabled. I have a large plastic funnel which fits into a smaller plastic funnel which fits in to the radiator fill port, and gives the coolant somewhere to expand.
Its a bit alarming but I think its better than risking local overheating by using the engine normally with an airlock.
Edited by edlithgow on 21/04/2022 at 01:43
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