The difference between the compression
tester and a leak down tester is the compression
tester one uses with the motor
being cranked over and has one gauge, which tells one the cylinder pressure.
A leak-down tester has two gauges. With the motor
piston in different positions in the cylinder one can check to see if the cylinder is warped or has other wear. As well, the valves could be leaking instead.
One pumps air into the cylinder up to certain pressures and the second gauge will tell you how long the air stays in the cylinder, to put it in simple terms.
You'll need an adapter for the injector hole for your motor what ever gauge you use.
If air is leaking out your exhaust/intake, it's valves. if air is leaking into the crank case then it's pistons/cylinders. Leaking anywhere else, its a gasket
(check the cooling