High-pressure Radiator Caps have a specific purpose. However, let’s start with what they DON’T do.
High-pressure caps will not solve overheating problems. For overheating problems, troubleshoot and/or upgrade these parts first:
If your current cooling system is running well and doesn’t overheat, a high-pressure cap is unnecessary. It won’t hurt anything. But it won’t help either.
When Should I Use One?
A high-pressure radiator cap is intended for race engines running little to no antifreeze. To understand why, you first need to understand:
Some race vehicles run straight water as coolant. They do this because water transfers heat better than a mixture. Also, many race tracks do not allow glycol-based fluid to be used. (Spilled antifreeze causes both safety and environmental issues.)
However, straight water has a lower boiling point than a mixture. A high-pressure radiator cap is used to raise the boiling point. This protects the system from boiling over at the top of the operating temperature range.
High-performance engines also create more heat. Higher pressure caps can boost the boiling point even more. Again, this protects the system from boiling over.
For Example
The coolant mixture and system pressure combine to set the boiling point. The chart below shows how these things affect each other. (This is just an example, not a recommendation.)
| Engine Type | Water/Coolant Mix | Cap Pressure | Boiling Point |
| Stock | 50/50 | 15 psi | 268° F |
| Modified | 70/30 | 16 psi | 268° F |
| Race | 100/0 | 19 psi | 269° F |
You can see that all the examples above have a similar boiling point. The increased system pressure offsets the reduced antifreeze content.
Notes
- With less or no antifreeze in your system, a Coolant Additive can help prevent corrosion, lubricate parts, and improve the cooling capability.
- For special uses, non-glycol, water-based, and waterless coolants are available.
- Details for using these products vary.
- Check the Instructions for specific recommendations.