Reading The Signs

Reading the Filter Once the filter media is free from the canister, you can take a moment to clean up any spilled oil before beginning your inspection. The trapped material in your filter media can tell you a lot about what's going on inside your engine, but first you have to be able to determine exactly what you are looking at.

Begin by tapping the filter element on a table to see if larger chunks of debris fall out, which could signal a serious problem. It is difficult to see smaller shavings of metal, which is what you will typically find when you have a problem, in the oil-soaked filter media. It's best to spread out the filter and look into the bottom of the folds.

What you are likely to find depends a lot on the state of the engine. After breaking it in, it's normal to see a small amount of material of all types in the filter media. But you should see far less in a healthy engine that has been running for a while.

One of the most difficult aspects of reading an oil filter is determining exactly what you've found. You can use a small magnet and run it across the filter to pick up any steel shavings. This separates any steel, which can be piston rings, parts of the cylinder wall, or any other number of things, from the non-magnetic metals left behind. What's left is most likely aluminum from the pistons or cylinder heads. Non-magnetic material can also be titanium, if you are running titanium valves or spring retainers. Another easy test to determine whether you are looking at aluminum or steel shavings in your filter is to rub it between your fingers. Aluminum is shiny and bends when you mash it between your fingers. Steel is less shiny and more likely to break when pressed between your fingers. Titanium is shiny, like aluminum, but breaks like steel instead of bending like aluminum.

Anytime you inspect your filter and find a lot of steel, it is cause for concern and potentially requires a teardown. Normal wear creates a small amount of steel shavings, especially in a new engine. This can come from the rings seating or the ridges in the cylinder bores' crosshatch being worn down. However, if you suddenly notice a lot of steel filings in your filter, you might be losing a camshaft, especially if you are running a flat-tappet cam with a very aggressive lobe design. You can also rub a bit of the motor oil between your fingers; if it feels gritty, that's another sign that you have a lot of metal shavings or other contaminants being picked up by the oiling system.

Aluminum flakes are less of a concern and usually originate from the piston skirt wearing against the cylinder wall. OEM-style aluminum bearings can also be a source. Most engine builders still prefer softer babbit bearings with a copper backing. This makes a bearing problem easier to spot because a disintegrating bearing will leave copper-colored filings in the filter media.

Finally, it is critical to clean your engine as well as possible before final assembly. This is a good engine-building practice that ensures anything picked up in the filter media isn't simply a leftover from before the build. After running a new build, the filter will almost always have lint from cleaning towels and small chunks of silicone, which is not a concern but should be minimized as much as possible. A greater problem stems from not properly cleaning the oil galleries on a rebuild. If a bunch of metal and rust gets flushed into the filter, you have no idea whether you are looking at remnants from a poor cleaning job or signs of a new problem, so check it carefully. Read your filter, save your motor!