Home           Last updated Tuesday, 2012-09-09

Your mechanic will charge you an hour of shop time to cut open and inspect your oil filter. You can do it yourself in 30 minutes and save some coin.

The first thing you should do is let the filter drain for a few hours into a suitable container.

Cutting the filter

The first couple of times I cut open an oil filter I did it with a hacksaw. While this will work, it takes longer, it is messier, and it can introduce misleading metal particles into the filter element.

There are a number of kinds of oil filter cutters. I suggest you investigate both "automotive" tools and "aviation" tools. You may find a wide price difference.

Photo #1 below shows the victim and the tool with which we are going to decapitate it. The cutter has a central bar which fits into the oil outlet on the filter, a cutting wheel which does the dirty work, and an adjustment screw which progressively deepens the cut of the wheel. If you cannot identify these components yourself in the photo below, I suggest you stop reading, hand your filter to your mechanic, and write a check.

As you can see the filter was installed on 4/22/12 when the tach reading was 4997.44. As will be seen in later photos this is a Tempest Filter, AA48110-2. These filters are a bit shorter than the standard 48110 and make installation and removal a bit easier. Oil flows into the filter through the four holes in the headplate and out the threaded nipple. This means that oil flows into the oil can, passes through the paper filter element into the central spindle. This is important to remember as debris will be on the outside of the filer element.

Photo #2 shows the cutter installed on the filter which is held in a vise by the nut on the bottom of the filter. Proceeding from here, one tightens the adjustment screw, turns the cutter, tightens the adjustment screw, turns the cutter, tightens the adjustment screw, turns the cutter, tightens the adjustment screw, turns the cutter, ...


Photo #3 below shows the cutting wheel having broken through the can. It may be helpful to turn the cutter alternately in both directions, clockwise and counter-clockwise to break off the filter top around the complete circumference. Note the paint particles created by the cutting wheel.


Photo #4 shows the decapitation complete. The element assembly floats free in the can on the right. The central rubber gasket which holds it securely in place during operation is visible on the left. The cutting wheel creates white paint splinters which can be seen on the top of the element assembly. These should be wiped off immediately after removing the element assembly from the can.


Photos #5 and #6 below show the bottom of the element assembly while draining the assembly. The left photo shows the leaf spring which holds the floating assembly tight to the top rubber gasket. The spring is steel and is simply held in place by a magnet on the base of the assembly. Remove the spring and examine both sides of it for metal debris attracted to the magnet. The right photo shows the doughnut-shaped magnet with the leaf spring removed. The magnet is glued to the bottom of the element assembly. Wipe the magnet with a clean paper towel and look for "sparkles" under a bright light. Any indication of metal should be shown to an A&P.


Photo #7 below shows the element assembly removed, wiped down, and having the paper filter cut out with a utility knife. Use a NEW blade, and follow the edge of the end caps, cutting all the way to the central tube. It will take a few times around to cut all the pleats all the way down.


Photo #8 below shows how to remove the element from the assembly. Find the metal fin and cut the bottom of the two adjacent pleats. With the circumference cuts along the end caps and freeing the paper from the metal fin, one can simply peel the paper pleat out of the assembly. Remember the oil moves from the outside of the filter to the inside, so all the debris will be caught by the outside pleats.


Photo #9 below shows the element removed from the assembly. The paper element is 2-1/2" high and 95" long for 1.65 square feet of filter performance. Examine every pleat under a bright light. Look particularly for sparkles from metal powder, splinters, and/or chips. Pick out items of concern and wipe onto a clean paper towel. Items may be cleaned in rubbing alcohol or vodka.


Photo #10 below shows typical debris. Black debris is generally carbon combustion products. Some times the carbon is hard, but will crush with a finger nail or small screwdriver. Sometimes it is more like tar. Grey or white debris can be bits of gasket material or more combustion products. Again it will crush easily. Small bits of gasket material may be seen after major engine work, but should diminish and vanish in a short time. Metal is of concern. A tiny bit here and there is not an issue. The two tiny slivers shown here where the only metal found in all the pleats. This engine was overhauled about 70 hours ago, so these tiny shavings are not unexpected. Metals distributed among many pleats, whether powder or particulates should be examined by an A&P.


Engine manufacturers have their guidelines regarding metal in oil filters. Lycoming's recommendations and suggestions are contained on page 8 in the Maintenance reprint of their set of Key Reprints available on their website.

Debris can be examined with a magnifier, can be tested with a magnet, can be tested for hardness, and can be tested with household chemicals to determine likely composition. This subject is beyond the scope of this simple page. I strongly suggest that if you find any quantity of metal in your oil filter you refer the matter to an A&P mechanic.

Oil analysis

I strongly suggest you routinely send an oil sample out for analysis. There are a few of these services. We have used Blackstone Laboratories for about a decade. Oil analyses are not magic prognosticators, but can give hints that your engine has or is quickly changing. If you plot your normalized values over time you can track trends and perhaps diagnose abnormal wear. The Blackstone website has much information and sample reports which you will find interesting and helpful.