In a recent "In The Shop" column in Farm Journal Magazine I made brief mention of using cooking flour or talcum powder to identify the exact location of small fluid leaks on farm equipment. At first glance, finding a hydraulic leak seems simple, and it is-- if the leak is an oozing, flowing or spurting-type leak. But when a slow, subtle leak is hidden somewhere in the midst of a complicated tangle of hydraulic valves, finding the exact seal or o-ring that's barely seeping can be a challenge. That's when it's time to powder the problem area and identify the exact location of that pesky leak.
First, use a power washer, or degreaser and a garden hose, to clean away all the accumulated glop and debris. Once bare metal is visible, spray the area with contact cleaner or brake cleaner and then use an air nozzle to completely and absolutely dry the area. For talcum-testing to work, the area must be absolutely, completely bone dry.
Once the area is clean and completely dry, dust it with talcum powder or cooking flour. I use the talcum powder used with air planters to lubricate their seed delivery systems. You can literally toss handfuls of talc or flour at the area in question, or use a "poof bottle" to accurately aim it at hard-to-reach locations. I made my "poof bottle" from a plastic one-quart gear lube container with a pointed cap. I emptied, cleaned and thoroughly dried the bottle before filling it half-full of talc. When I squeeze the plastic bottle, a small hole in the pointed tip "poofs" a stream of talc wherever I point it.
When the suspected area has at least a thin coating of white powder, start the machine and run all hydraulic functions through their full range of motion. The goal is to pressurize any hydraulic component that might pass oil through the suspected area. There's no need to run the machine for a long time---the super-dry talc or flour will discolor when exposed to even miniscule amounts of liquid. In fact, it's often best to run the machine only briefly, so you can pinpoint the first sign of discolored powder, before it expands, migrates and possibly confuses its point of origin.
Powdering a machine is a killer way to pinpoint fluid leaks. I've diagnosed leaks that were little more than wet spots that barely accumulated dust during harvest season. I've determined whether antifreeze was leaking from a radiator core tube or where the core tube attached to a lower radiator tank. I used powder to determine that a persistent leak on a hydraulic pump was actually due to casting flaws that left the housing slightly porous.
So, if you ever notice that your favorite mechanic has a container of talcum powder on his tool chest, don't assume he has a rash or chafing problem. He's probably just prepared to diagnose subtle and persistent fluid leaks on farm equipment.