General Question

whitetigress's avatar

Should I run the car with the radiator cap off to allow air bubbles to escape?

Asked by whitetigress (3129points) December 18th, 2011

This is for an installation of my Nissan 200 SX-SE radiator.

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7 Answers

DrBill's avatar

as log as you have it connected correctly, with a reserve tank, it will expel the air on it’s own with the cap in place. It is common to fill the radiator and run the engine with the cap off until it cycles at least once, to get the bulk of the air out.

jerv's avatar

I have done so for brief periods, but never with under conditions other than “vehicle parked, hood up”. Sometimes it’s the only way to fill the system though, so it’s not automatically a bad thing.

judochop's avatar

Buy a breather cap and take it for a ride on the highway but let it sit running with out the cap in the drive for a good fifteen minutes or until hot.

filmfann's avatar

I am with @jerv here. Parked, hood up. When the thermostat gets hot enough, the water will cycle through the engine, and you will see the water level drop. Quickly add water and cap it.

john65pennington's avatar

You have an overflow tank for this purpose. The air will escape through the hose attached to the radiator cap and disipate in the overflow tank.

Leave the cap on and be cautious of the heat and steam from it.

It will burn you.

Skaggfacemutt's avatar

Can you even do that? I thought the water would all come spraying out.

jerv's avatar

@Skaggfacemutt You can and it won’t… unless you open it while it’s hot. A cold engine has no pressure in the cooling system; a hot engine has around 15 psi. If you release the pressure slowly (and there are special caps to do that easily and safely, and a way to do it with a regular cap), you can even take the cap off of a hot system without being sprayed, but I don’t recommend it unless you know the trick; too dangerous for the untrained.

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