Make an Auto Radiator Pressure Tester


Step 13: Attach the gauge

Picture of Attach the gauge
The tire gauge will attach to the other shorter piece of fuel line hose. Clamp with small hose clamps.

You have now finished your radiator pressure tester. It should look like the photo in step 1.

Attach the stopper to the neck of the radiator. See step 11. Attach a bicycle pump to the valve stem. See step 12. Your car's engine should not be running. Pump the system up until the gauge reads 15 pounds. Often you can hear a hiss where the system is leaking. You may see evidence of moisture appearing where the leak is located. You will also notice that the pressure reading on the gauge leaks down slowly after a few minutes.

Sometimes the pressure reading does not leak down, but you know your system has a leak. In those cases, chances are the leak is coming from your radiator cap. If the cap is a few years old, replace it and see if your loss of coolant has ceased.

I have used this tester several times and it was always a big help.
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Here' s a stupid question, why pressurize at the radiator cap?  Why not pressurize at a heater hose at the thermostat bypass?  Sure its a little more involved and you might drip a little but it should be able to pressurize anywhere in the system you like, right?

farna5 years ago
What about using an old radiator cap for the stopper? I'm thinking drill the rivet holding the spring in out, then use a large piece of rubber instead of wood for the plug. Maybe a piece of foam and a thin wood plug with flat rubber face. The plug would have to compress to hold pressure. Hmmm.... maybe leave the original spring in and just make a new face with the valve stem running through, holding the thing together. Like the commercial kit, youd need to make several plugs to match different size caps. You could use it on a sealed cooling system (with a pressure tank and no cap) also -- get an extra cap and epoxy a tube to it. Most of the pressure tanks have a small hose connected somewhere also. Would be easy enough to remove the hose from the tank, plug the loose end, then pressurize the tank through the hose barb.