Parts for your 2018 Ford Ranger-Radiator cap

2018 Ford Ranger radiator cap — what’s actually fitted and what to service

For the 2018 Ford Ranger (PX MkII/MkIII), there isn’t a traditional radiator cap on the radiator itself. Ford’s design uses a pressurised coolant expansion/degas bottle with a pressure cap on the reservoir. This is confirmed in Ford’s 2018 Ranger Owner’s Manual (Cooling/Engine Coolant section), which instructs owners not to remove the coolant reservoir cap when hot, and in the Ford Workshop Manual, Section 303-03 (Engine Cooling), which details filling, bleeding and pressure checks via the degas bottle rather than a radiator neck. So while many people search for a “radiator cap,” the part to service on this ute is the coolant reservoir (degas) cap.

Why Ford doesn’t fit a radiator cap to the radiator on this model comes down to modern cooling system logic. The sealed, pressurised reservoir is the high point of the system, where air is purged and coolant expands and contracts without stressing hoses and cores.

• Better deaeration: The degas bottle lets air separate from coolant continuously, cutting the risk of hot spots.
• Consistent pressure control: The spring-loaded reservoir cap holds the cooling system at its rated pressure for a stable boiling point and improved reliability.
• Service access: All filling, bleeding and testing happens at one safe, accessible point under the bonnet.

What owners should actually check and replace is the coolant reservoir pressure cap. If that cap can’t hold the specified pressure, the engine can run hotter, push coolant out, or pull air in on cool-down.

1. Only open the reservoir cap when the engine is stone cold. A hot system can release scalding coolant.
2. Inspect the cap’s rubber seals for hardening, cracks or nicks. Replace at the first sign of damage.
3. Check the cap’s pressure rating printed on the top and match it exactly when replacing. Using the wrong kPa/psi can cause overheating or hose/coil damage.
4. If there’s unexplained coolant loss, sweet coolant smell, collapsed hoses after cool-down, or frequent overheat warnings, get the cap pressure-tested as part of diagnosis.
5. When refilling after work, use the correct Ford-approved coolant and bleed the system via the reservoir per the Workshop Manual procedure.

During routine servicing, it’s smart to treat the reservoir cap as a wear item. They’re inexpensive, and a fresh, correct-spec cap is cheap insurance on long Kiwi or Aussie runs with a loaded tray or towing a van.

Does a 2018 Ford Ranger actually have a radiator cap?

No. It uses a pressurised coolant reservoir (degas bottle) with a pressure cap, not a cap on the radiator itself. Ford’s manuals specify filling and bleeding at the reservoir and warn against opening that cap when hot.

What pressure rating should the cap be on a 2018 Ranger?

Use the exact kPa/psi rating printed on your current cap or specified in the vehicle documentation for your engine variant. Don’t mix ratings—too low can cause boil-over, too high can stress hoses and the radiator.

How often should the cap be replaced?

Have it inspected at every service. Replace it if seals are perished, if it fails a pressure test, or if you’re chasing cooling issues like coolant loss or erratic temps. Many owners proactively replace the cap every few years as preventative maintenance.