Is it absolutly necesary to remove all of the plugs while doing a compression test? I am just looking for one that may be the cause of my coolant in oil problem. I had thought it was my oil cooler but the oil level is rising again so it was not.

 

To test all cylinders and compare accurate readings, all plugs should be removed. Can it be done without removing all plugs? Yes, but results may not be so accurate. A large problem would probably be easily evident, though.