Eric,
These are some notes I had cut and pasted to save over the years. I did not write these, but I'm sure they came off of TDS about 2 years ago when I was looking.
Most likely the easiest test is a a combination of two. The first being a coolant system pressure test. This is very simple as instead of applying pressure to each cylinder, it is applied to the entire cooling system. This test is usually done to about 25-30 psi and will show a leakdown of any coolant joint, or a through hole in a cylinder. Test kits are available from any auto parts store. One thing to keep in mind though, a leakdown will not necessarily mean a back block, it may be a bad pump, hose joint, etc. The second test is to measure the pH of the coolant. As exhaust gases are passed into the coolant, it will become acidic. This will also indicate early head gasket failure (although in diesels, there is a permissible blowby which is acceptable due to the high compression ratio).
Another check is at initial start up. Usually this is done in conjunction with test #1 (pressurize the cooling system). As on cold start up, with a pressurized cooling system, cylinder leakage should show up as vapor or excessive water from the tailpipe, this is due to no catalyst function on a cold start. Also check the oil for signs of any water/coolant present. As on shutdown, a cylinder hole will continue to flow into the cylinder, past the rings, and into the crankcase.
To accurately pinpoint the cylinder leaking the full steps are as follows:
1. Warm up the engine
2. Remove all glow plugs
3. Remove valve covers, rocker arms, and pushrods
4. Using an adapter that threads into the glow plug hole, attach compressed air (100-175psi)
5. Wait 3 mins for each cyl being tested.
6. A failed cylinder will make the Coolant level slowly rise and then overflow from top of radiator. It won't blow out of the radiator, but it will be obvious.
NOTES:
o Valve train should be removed to allow the piston, in the cylinder to be tested, to drop to BDC when shop air pressure is applied. This insures the valves will be closed and the entire cylinder surface can be tested under pressure.
o You can purchase an air pressure adapter at most tool shops (they normally are sold to adapt a compression tester to the glow plug hole)
o The cylinders that are most prone to cavitation are listed in order. #8, #7, and #4. Be sure to test all cylinders as I have seen some of the other cylinders occasionally deviate from this norm.
o Most coolant leaks into the cylinder will show as the glow plug tip will be wet on the bad cylinder.