Very quick question
 

I got a pressure tester for my coolant, now what P.S.I do I pump it to??? It says in the manual not to pump more or equal to 30psi.

Most systems are regulated by the cap at 15PSI. Also use the tester to test the cap to ensure that it relieves pressure at 15PSI.

Good luck,

Look on the cap. MB caps have come with 100, 120, and 140 on them. This refers to 1bar, 1.2 bar and 1.4 bar. A bar is 14.2 psi. The system must be able to withstand the pressure that the cap releases at. If the cap does its job thats the highest pressure it will ever see.

Should be lesst than 20 to 25 psi, if more than that u might damage some seal and gasket, and the rubber hose.