I had a homemade leakage tester years ago when I had my garage and it was very simple and worked great. It had two gauges on it with an orifice between the two gauges. You simply put 100psi into one end and the other end went into the cylinder. You put air in until the first gauge read 100psi and read the pressure on to other gauge. If it was down to 90psi you knew you had a ten-percent leakage in that cylinder.

I spotted one at Harbor Freight and thought I couldn’t buy the gauges and make one as cheap as the one from Harbor Freight. I read the directions when I got home and it doesn’t make sense. It says on page 6 of the directions to hook it up and then turn up the pressure until the leakage gauge reads zero and then read the percentage of leakage. What the heck do they mean? You just set it to zero so it is going to read zero. What am I missing here. The only thing I see with the tester on the engine is the input gauge reads 15psi to get the leakage gauge to read zero on a good cylinder and it takes 20psi to get the leakage gauge to read zero on the suspected bad cylinder. How can you relate that to percentage of leakage?

Has anyone used one of these from Harbor Freight and can enlighten me s to what I am not getting here.