Ford Fiesta: EcoBoost 1.0T coolant expansion tank cracking and coolant loss

The plastic coolant expansion tank on WZ Fiesta 1.0T EcoBoost models is prone to stress cracking, causing coolant loss that leads to overheating. This is a widely reported failure on EcoBoost 1.0T engines across the Fiesta and Focus platforms and is documented across multiple Ford owner forums in the UK, AU, and NZ markets. Coolant loss is particularly dangerous on this engine because overheating is linked to premature wet timing belt delamination. The tank typically cracks at the weld seam or at the cap-mounting boss.

• Coolant warning light or temperature gauge rising above normal
• Coolant puddle or staining under the engine bay
• Frequent need to top up the coolant reservoir
• Sweet-smelling vapour from the engine bay when hot

1. 1

   Inspect the coolant expansion tank for cracks, discolouration, or calcium deposits indicating past leaks.

2. 2

   Check the coolant level against the min/max marks.

3. 3

   Inspect the cap-mounting boss and tank seam closely.

4. 4

   Check for milky coolant which would indicate head gasket involvement.

Parts involved: Coolant expansion tank.

$200 to $500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the coolant expansion tank been replaced?”
• “Has the coolant level ever dropped unexpectedly?”
• “Has the temperature gauge ever moved above the normal range?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.