Pictured is a commercial radiator pressure tester. They are relatively expensive for the DIY home mechanic. But, there are times when it would be very handy to have a radiator pressure tester for finding leaks leading to coolant loss and possible engine overheating out on the highway. (The photo is from Google images.)
Step 1: My homemade tester
When we had one youngster in college, another in high school, and my wife was working we had four cars in the driveway for a while. We had another child out in her own apartment, but she always brought her car to dad when it needed to be fixed. It was not uncommon for one of these cars to have a mysterious coolant system leak. I made this pressure tester so I could locate and fix such leaks quickly.
Step 2: Compatible vehicles
My pressure tester works on radiators with a neck and cap on the radiator. I have not used it on closed radiators that are filled through a coolant recovery bottle. It might be possible to adapt it for fitting onto the fill opening in a coolant recovery bottle, but I have not had to try it yet.
Step 3: Tire pressure gauge
I selected and bought a dial indicator tire pressure gauge identical to this one. Its outside diameter at the end fits nicely inside a piece of 5/16 inch I.D. fuel line hose. This gauge holds pressure until the brass release button on the side is pressed. You will want to watch the gauge to see how fast it leaks down when the tester is in use. I removed a valve core from the end of the gauge before attaching it. Another option is to use a gauge that does not have a pressure release button. (The photo is from Google images.)
Step 4: Tire valve stems
Buy a package of tire valve stems. I used a sanding drum to remove the expanded section where the stem attaches to the steel rim. See the yellow lines. You will need two valve stems. (The photo is from Google Images, but edited by me.)
Step 5: Plastic Tee
You will need a 5/16 inch plastic tee. (The image is from Google Images.)