Source to get a pressure tester
If there is an AutoZone store in your area, go there and rent one. I rented one two days ago. I paid $75 and will get my money back when I return it. Pressure test the cap. Mine caused the car to overheat. I personally suggests replacing the one you got and the sensor along with a new mounting kit that inclues an O-ring, snap ring, and the male part connector.All parts are about $35. A 100 miles after I put the head back on the car (3 days ago), the car lost antifreeze/water and got mixed with oil. My sensor was dead and it was ordered before I even test drive the car, however, it was late. The head came back from the shop today and it was fine. The first machine shop that had it did not machine the surface right per the second machine shop and water/antifreeze fluid leaked into the cylinders. You will need a snap ring plier to get the ring out.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer