My Volvo excavator has a sick Mitsubishi S3L2 3 cylinder diesel. Excessive crankcase pressure (oil spray out of the dipstick tube), starts hard, feels like its not running on all cylinders when cold. I've picked up a nice old MAC compression gauge but have a few questions. I pulled the glow plugs and cranked it over, taking the highest reading of each cylinder. Numbers were 450#, 400#, 550# Reading through the manual, which is NOT very clear, it states that I should just crank it over till I get a reading. If I do that, not allowing each cylinder to pump up, my numbers are more like 250, 200, 300. So, whats the "correct" way to measure compression? I mean, it seems like this poor thing has earned its retirement, but I feel like I should know how to properly use this gauge for the future.
In my mind, in order to get a proper reading you should spin it over until the pressure readings peak. That's how I've always done it anyways.
Sounds like there’s hole in the piston.
Yes, crank until you top off at the highest PSI. Best case readings are supposed to be around 10% of each other. Sounds like time to do a leak down on those 400 & 450psi holes.
thanks for the quick replies. What is the procedure for a diesel leak down test?
Have an air compressor available? You can buy an actual leak down tester and adapt it to your glow plug compression adapter (with the valve stem removed); this will show you how much air you're putting in and how much is getting out. You'll be able to hear where it's coming out of (intake, exhaust or crankcase). If you don't plan on buying the actual tester, you can either control air pressure at the compressor or use a ball valve/knob adjustment inline to the glow plug adapter. Usually you'd bar the engine over and do each cylinder at TDC, but it's much easier to pull the valve cover, loosen all the rockers and just test each cylinder that way. At worst you'll know where the issue is and get the valves adjusted so you can drive it out of the shop.
New low hour engine on the way, $1500 shipped to my door. I'll strip this one down for spare parts.
A hole with 400lbs pressure??