Parts for your 2018 Ford Fiesta-Radiator cap

2018 Ford Fiesta radiator-cap — is it even a thing?

Short answer: a traditional radiator-cap isn’t used on the 2018 Ford Fiesta. Ford’s own literature — the 2018 Fiesta Owner’s Manual (Cooling System section) and the Ford Workshop Manual (Section 303-03, Engine Cooling) — specifies a sealed, pressurised cooling system that fills and vents through a remote expansion tank (often called a degas bottle). The pressure cap lives on that tank, not on the radiator itself. So if someone’s hunting for a “radiator-cap” for a 2018 Fiesta, what they actually need is the coolant expansion tank cap.

Why did Ford set it up this way? Modern compact engine bays and tighter emissions/thermal targets make the remote tank the smarter spot for pressure control. Mounting the cap on the bottle gives a higher fill point for better self-bleeding, keeps hot coolant away from the radiator top tank, and simplifies packaging under the bonnet. The Fiesta’s radiator doesn’t have a filler neck at all — it’s a closed unit plumbed to the pressurised bottle with the cap doing the pressure and vacuum relief duties there.

What owners should do instead of chasing a radiator-cap: check and top up only via the expansion tank. The cap on that bottle is the service item. If the car is losing coolant, runs hot, or there’s a sweet coolant whiff after a drive, the cap’s seal or pressure valve may be tired. A workshop can pressure-test the cap and system, many Ford caps are around the 20 psi (≈138 kPa) mark, but always match the rating printed on the cap and confirm against the owner’s manual or by VIN with a parts counter.

Practical tips for the 2018 Fiesta’s cooling setup:

• Never open the cap when hot — wait until it’s stone cold.
• Check the cold level sits between MIN and MAX on the bottle.
• Use the Ford-specified coolant type and colour noted in the owner’s manual, don’t mix types.
• Treat the expansion tank cap as a wear item: replace if the seal is cracked, swollen, or the spring action feels weak, or proactively around major cooling service intervals.

All of the above aligns with Ford’s documented system design for this model year, which calls the reservoir a “degas bottle” and specifies service fill and pressure control via that bottle rather than a radiator-mounted cap.

Popular questions about the 2018 Ford Fiesta radiator-cap

Does a 2018 Ford Fiesta actually have a radiator-cap?
No. It uses a sealed, pressurised expansion tank with the cap on the bottle, not on the radiator. Owners add coolant and manage pressure via that cap only, as outlined in Ford’s Owner’s and Workshop Manuals.

What pressure rating cap should a 2018 Fiesta use?
Match the rating printed on the existing cap and confirm against the owner’s manual or with a parts supplier by VIN. Many Ford small cars run caps around 20 psi (about 138 kPa), but the exact spec should be verified for the vehicle’s engine and market.

Where is the cap and how do you top up coolant?
The cap sits on the translucent plastic expansion tank in the engine bay. When the engine is fully cold, remove the cap, top up to the MAX line with the Ford-approved coolant mix, refit the cap, and drive normally. The system is largely self-bleeding for minor top-ups, for full drains, a proper bleed or vacuum fill per workshop procedure is best.