Good day,

I recently lost the radiator cap. We have a spare radiator cap and it fits, but I'm not sure if it's for the same pressure.

How do I know if it's okay? If I cannot avoid driving, is it safer to drive without the cap than with a cap that could be for a different pressure?

1 Answer 1


It's by far better for your vehicle than to run without one. The replacement radiator cap is going to be fairly close in pressure to your original one. The system should be able to handle it if it's a couple pounds higher or lower. The cooling system will not work anywhere close to correctly without a cap on it and you'll most likely never make it to your destination without overheating. If you have to drive, use the cap.

  • Most cooling systems pressurize the same amount, don't they.
    – tlhIngan
    Oct 9, 2016 at 4:45
  • @tlhlngan - I'd say within a pound or two of each other, yes. Oct 9, 2016 at 12:00
  • Modern systems with a reservoir run at a much higher pressure than older systems with just an overflow tube that spat excess on the ground. The pressure ranges can be from 4 to 30 psi (30 to 200 kPa).
    – user16128
    Feb 24, 2020 at 8:16

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