What psi radiator cap do I need?

The psi rating you need is the one specified by your vehicle’s cooling system design. Most passenger cars use a cap around 13 to 16 psi, and you should verify the exact rating on the cap itself or in the owner’s manual.

A radiator cap controls the pressure and vacuum in the cooling system, helping prevent coolant loss and controlling boiling temperature. Using the wrong rating can lead to overheating, leaks, or other cooling problems. This guide shows how to identify and confirm the correct psi for your car.

What the psi rating means for your cooling system

The cap’s psi rating is the maximum pressure the cooling system is designed to tolerate before the cap vents excess coolant or pressure. Matching the OEM rating ensures the system maintains the intended boiling point and pressure balance, reducing the risk of overheating or hose damage.

Reading the cap markings

Most radiator caps display the rating directly on the cap, such as "13 PSI" or "16 PSI." Some caps use metric bars (for example, 1.1 bar ≈ 16 psi). If the rating isn’t clearly visible, check the vehicle’s service data or contact a dealer with your VIN.

How to determine the correct cap for your car

To ensure you pick the right cap, begin with these checks.

• Consult the owner's manual or official service data for the recommended cap rating (typical passenger cars: about 13–16 psi).


• Inspect the current cap for a stamped rating (e.g., "13 PSI," "15 PSI"); the existing cap is often the safest reference.


• Note whether your cooling system uses a radiator cap, a reservoir cap, or both; mismatch between radiator and reservoir caps can cause improper venting.


• If you’ve modified the cooling system or engine, verify that any upgrade still falls within the system’s design limits; do not exceed the radiator’s capacity.


• When in doubt, replace with the OEM cap that matches the original part number or have a dealer confirm the exact rating for your model.

Conclusion: By checking the manual, inspecting the cap, and confirming reservoir/radiator compatibility, you can confidently select the correct psi rating for your cooling system.

Common PSI ranges by vehicle type

While OEM specifications vary, these ranges cover many common scenarios. Always verify with your specific model to avoid mismatches.

• Older or smaller engines: 7–9 psi (0.5–0.6 bar).


• Most modern passenger cars: 13–16 psi (0.9–1.1 bar).


• Performance or turbocharged engines: 15–19 psi (1.0–1.3 bar).


• Some high-performance or specialized vehicles: up to 18–22 psi (1.25–1.5 bar).

Note: These ranges are approximate. Exact ratings depend on the original design of your cooling system, so always confirm with OEM data or a trusted technician.

Practical steps to replace or verify a cap

1. Park the vehicle on level ground and ensure the engine is cold before opening any cap to avoid scalding from pressurized coolant.


2. Remove the reservoir or radiator cap and inspect the seating surface for damage or cracks in the seal.


3. Check the rating on the replacement cap to match the OEM specification exactly; do not mix ratings.


4. Install the new cap securely, then run the engine to operating temperature and check for leaks or abnormal pressure behavior.

Conclusion: Replacing a mismatched cap with the correct rating restores proper pressure control and helps prevent coolant loss or overheating.

Summary

In short, the right radiator cap psi aligns with your car’s original cooling system design. Locate the exact rating in the owner’s manual or on the existing cap, verify whether you have a separate reservoir cap, and choose an OEM-approved cap with the same rating. For most cars, the common range is around 13–16 psi, with some performance or older vehicles operating higher or lower. When in doubt, consult the dealer or a qualified mechanic to ensure you select the correct rating and size for your vehicle.

Will a 15 psi radiator cap raise the boiling point of coolant?

With every pound per square inch (PSI) placed on the cooling system, the coolant's boiling point raises approximately 3°F. A 15 PSI pressure cap twisted onto the radiator will result in a 45°F boiling point increase over the 220°F for a 265°F boiling point.

How many psi is a 1.1 radiator cap?

A 1.1 bar (bar) radiator cap is equivalent to approximately 15-16 psi and raises the boiling point of the coolant, which can help prevent overheating, especially in high-performance applications or hot climates. This pressure rating is higher than many factory caps (which might be 0.9 bar or 13 psi) and can improve cooling efficiency, but it should only be used if your cooling system is designed to handle the increased pressure to avoid causing leaks in old hoses or seals.
 
Function and benefits

• Increases boiling point: The primary function is to increase the boiling point of the coolant. A 1.1 bar cap raises the boiling point to about 122°C (252°F).
• Improves efficiency: It can improve cooling efficiency, especially in high-stress situations like track driving or in hot weather.
• Reduces coolant loss: The higher pressure reduces the chance of coolant boiling over and escaping into the overflow tank. 

Potential drawbacks

• System compatibility: It's crucial that the cooling system components (radiator, hoses, and seals) can handle the extra pressure. 
• Risk of leaks: If your system is old or has weak components, a higher-pressure cap can cause leaks. 
• Not a substitute for a healthy cooling system: A higher-pressure cap won't prevent general overheating if there's another problem, like a faulty water pump or a clogged radiator. 

Before installation

• Check your vehicle's manual: Always confirm the correct pressure specification for your vehicle in the owner's manual to ensure you buy the right cap. 
• Inspect system components: Make sure all parts of your cooling system are in good condition. If components are old or weak, it is safer to use the original pressure cap. 

What happens if I use a higher psi radiator cap?

If the radiator cap pressure is too high, it can cause the pressure to build up and lead to the coolant system bursting or leaking, with visible signs including leaking coolant, overflowing coolant reservoirs, and steam from the engine. The excessive pressure can also lead to engine overheating, collapsed hoses, and potential damage to the radiator, gaskets, or seals. 
Consequences of excessive pressure

• Overheating: High pressure can impede the circulation of coolant, leading to overheating. 
• Component failure: The cooling system is designed for a specific pressure; excessive pressure can cause it to burst, damaging the radiator, gaskets, and hoses. 
• Coolant leaks: As pressure builds, it forces coolant out of weak points in the system, leading to leaks. 
• Coolant overflow: Excess pressure can force coolant into the overflow reservoir, causing it to overflow and potentially leak onto the ground. 
• Steam from the engine: When the pressure becomes too high, it can result in steam escaping from the engine, which is a sign of a serious cooling system failure. 
• Collapsed hoses: In some cases, the pressure can cause radiator hoses to collapse. 

Why the right pressure is crucial

• A radiator cap's function is to maintain a specific pressure within the cooling system. This pressure raises the boiling point of the coolant, preventing it from boiling over at normal operating temperatures. 
• If the cap pressure is too low, the coolant can boil prematurely. 
• If the cap pressure is too high, it puts excessive stress on the system and can lead to component failure, as described above. 
• For these reasons, it's crucial to use the correct radiator cap with the pressure rating recommended by the vehicle's manufacturer. 

What psi radiator cap for Chevy 350?

A stock Chevy 350 typically uses a 15 PSI radiator cap, though some sources suggest 12 to 15 PSI is standard. A 15 PSI cap is a good starting point as it raises the coolant's boiling point without putting excessive strain on the cooling system's hoses, gaskets, and other components. For high-performance or modified engines, a higher pressure cap (up to 18 PSI) may be used, but this increases stress on the system and should only be done after confirming all components are up to the task. 
Standard vs. high-performance

• Standard engine: A 15 PSI radiator cap is the most common and recommended pressure for a stock Chevy 350. 
• Performance engine: Modified or "stroked" 350s may benefit from a higher pressure cap (18 PSI or more) to manage higher operating temperatures, but this can cause leaks if the rest of the system isn't built to handle the pressure. 

This video demonstrates how to pressure test a cooling system to check for leaks: 43sBleepinJeepYouTube · May 19, 2017
Why pressure matters

• Raises boiling point: The primary function of the pressure cap is to raise the boiling point of the coolant. For every 1 PSI of pressure, the boiling point increases by about 3°F. 
• Prevents overheating: By raising the boiling point, the cap prevents the coolant from boiling over and maintains a more stable operating temperature, especially under load. 
• System strain: Installing a cap with a much higher pressure than the system is designed for can cause leaks or damage to hoses, gaskets, the water pump, and the radiator itself. 

You can watch this video to see how to install a radiator cap on a 350 Chevy engine: 1mMatt's ShopYouTube · Jan 12, 2025
How to choose the right cap

• Start with the recommendation: Begin with a 15 PSI cap unless you have a specific reason not to. 
• Check the vehicle's specifications: If you're working on a specific year and model, check the original manufacturer's recommendations.
• Consider system upgrades: If you have a high-performance engine, research the specifications for all of your cooling system components to ensure they can handle a higher pressure cap before you install one.