At the dealer I diagnosed dozens of engines by the air test & I made up an adapter from a nozzle nut & used an air regulator & shutoff valve.What you do is take the nozzle out & screw the adapter in the chamber & bring the engine up on TDC for each cyl. your checking & set the regulator for about 90 lbs. & shut the air off & observe the leak down in the cyl. & also with the radiator full observe if there are bubbles in the coolant.If not go to the next cyl. and do the same procedure & go through all of them till you check them all.If you find just one that leaks into the cooling you could remove that chamber to check it for being bad but if it,s ok then I,d suggest to remove the head as it almost has to be a crack or head gasket anyway so either way it has to be removed. Cat did make a dummy nozzle that was just a hollow shaped nozzle to pump the air down inside the engine for this type test as they recommened the test to determine a problem like this.This testing I found to be so helpful & always proved the problem one way or the other.Also with the head off then you can again almost tell if it,s a bad gasket or a bad head or low liner etc.The nut for a D4 is 4F5677 that holds the nozzle down in so all you need to do is weld a pipe nipple or whatever you need to connect your air line to the nut & you need the seal under the nut to seal (5B3718) it tight so air doesn,t leak by it.Again make sure your on TDC firing stroke for the test on each cyl.and make sure the throttle is off.Also if the engine wants to turn with the air in the cyl. then lock the brakes & put in low gear with the clutch engaged for each cyl. test. I never really had a problem of it doing that but some say they have.

I have made a quick and dirty leakdown tester by pulling the rubber tip off of an automotive compression gauge which just happened to fit over a 1/4" pipe nipple. The tip just happened to fit in the prechamber where the nozzle goes. I was able to hold it down by hand against 120 psi. Like SJ says a leakdown test will tell you all you need to know about the upper end. Water getting into oil might be liner seals, you might have to pressurize cooling system to track that down.

8C I,m sure that your setup works good but you have to hold it so if you have one that is fixed into the chamber you can let it set & walk around & observe what,s going on in the radiator unless you have a helper which is a good thing anyway.I,m sure you have found problems doing this test & was introduced to us by the Cat factory & they made the hollow nozzle available as a dealer tool.With that you need an old fuel line or just the nut to make up the adapter to screw to the nozzle body.

SJ,
I like your rig using just the hold down nut off the injector, you will get a lot more flow into the cylinder that way than through an old injector line plumbed onto the adapter and the hollow nozzle. I checked the 9U the other day through mine and even though it has only a short section of injector line, I believe my gauge reading was a lot higher than the pressure in the cylinder. I am going to find an old nut and make me one with just the airline adapter on the nut just for pressurizing and leak checking the cylinders, not so much for evaluating leak down by the rings etc.

I couldn't show any leakage into the radiator with the air pressure. We had been seeing a pretty steady bubble while it was running. Maybe a cracked head that would get worse while hot?

Well....maybe I'm missing something here but I can say I have never checked a diesel engine with an air leak down test. Could never see the point....if you are getting readings from 100 psi shop air the problems are pretty obvious. To me it takes a running engine with combustion pressures and temperatures to get meaningful results where you can hear spitting valves, you can observe blow by (smoke) and pressurized crankcases and bubbles in radiator and see water in oil or fuel in water and cracks and pin holes have a chance to open up. Maybe in a shop environment there is some merit to a proof test but with few exceptions it's heads off for repairs time anyway.
I do occasionally do a cooling system pressure test but that to is limiting compared to combustion pressures. A leak down test may confirm a problem other than combustion related. As a liner seal check for example.

I'm open to suggestions:D Never to late to learn.......but time isn't waiting;)

I guess I am looking for which cylinder to look at closely when the head comes off:D Also a lot easier for me to hear a slightly leaky valve when the rest of the engine isn't making racket. I would say it's not the obvious ones that I want the extra information on.

I think the leakdown test is invaluable before the head comes off. If a cylinder is leaking down it can be easily pinpointed as to whether it is going through an intake valve, exaust valve, into the cooling system or into the crankcase.

You are right 8C it does prove lots of info & Caterpillar was the one to bring the test procedure out in the first place & went as far as to make up the hollow nozzle type tool for doing the job but using the top hold down nut works just as well as everyone doesn,t have the tool. I used it for years at the dealer on many engines & was very informative. Customers are very particular when it comes to diagnosing problems & want to know what they are in for before they say go ahead with the job as you don,t just guess to them what the problem is.

Well I might give it a go if I have a situation that is not able to be diagnosed but with the many options to checking a running engine I can't think of when that will occur. I don't have customers to prove anything to so that's not a requirement. I'm also not in the habit of fixing one cylinder. If there is a valve problem I usually inspect,fix, lap, or grind them all. I'd be curious to know if Cat still uses the air leak down check as a shop procedure now that everything is electronically diagnosed.

Greg,
From what I have seen, a head will typically crack due to heat in or around the exhasut valve seat area or between the exhaust valve and the precup. this type of crack will allow coolant into the cylinder and will cause white smoke. This will get worse as the engine warms up. If you shut it down, the coolant will continue to flow through the crack and can hydrolock the engine. I do not think this is your problem. I seriously doubt that this is cracked due to freezing as you would see signs of the freeze damage in other parts of your machine. For these reasons I would lean more towrds the head gasket. When and if you take the head off make sure that both the deck surface of the block and the head are flat and not warped. Hopefully it is neither of these. If you were getting coolant in the oil it would get milky fairly quick. You can always take an oil sample. Your local cat dealer can tell you what is in the oil that should not be. The last time I had this type of test done it was around $30. This might be a cheap way to make absolutely sure wether you have a problem or not. Have a good one!