Thoughts and advice on the care and feeding of fine automobiles from Machine Aficionado and bestselling author John Elder Robison, owner of JE Robison Service in Springfield, Massachusetts

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Everyone knows that oil filters are supposed to trap particles that might otherwise damage the engine.  

In a modern engine the passages that carry oil to the bearings are typically between one-tenth and one-quarter inch in diameter, which means that a good sized chunk of debris or sludge may block them.  The clearances between rotating parts like the crankshaft and the bearings is generally no more than a few thousandths of an inch.  That is tight enough that a grain of sand can get jammed in there and do considerable damage.

The filter is a modern engine’s protection against that. Nowadays the oil filter is immediately downstream of the oil pump, so the filtering happens before the oil reaches any bearing surfaces. All the oil that passes through the pump should pass through the filter, which is why today’s systems are said to have “full flow filtration.”

Most of the time the particles trapped by the filter are invisible but in this example the benefit of the filter is obvious.  The car in question is a 2008 Mini Cooper S.  Like many of its brothers this Mini had a problem with the timing chain and guides.  In this particular car the plastic guides were broken by the chain, and they landed in pieces in the sump.  The car was repaired with a new chain kit, but some pieces of plastic remained hidden in the sump.

Five thousand miles later this was the result. The bits of plastic that were left behind pushed through the oil pump inlet screen and passed through the pump gears.  Then they flowed into the filter, where they were trapped and held.

The filter looks scary, but the simple fact is, it did its job.  If this car had not had a filter - or if it had a cheap aftermarket filter that ripped – this engine would be toast today.  As it is, a new filter and fresh oil sent the car on its way.

Oil filters need to have filter paper or felt that is fine enough to catch the smallest abrasive particles yet strong enough to resist penetration by larger sharp-edged objects.  I hope you can see from this example that a good oil filter is all that stands between you and a $10,000 engine replacement.  Given the minimal cost of a OEM-grade filter, this is not an area where it pays to cut corners.

John Elder Robison

(c) 2016 John Elder Robison
John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent BMW/MINI, Mercedes, Land Rover, Rolls-Royce and Bentley restoration and repair in Springfield, Massachusetts.  John is a longtime technical consultant to the car clubs, and he’s owned and restored many fine British and German motorcars.  Find him online at or in the real world at 413-785-1665

Reading this article will make you smarter, especially when it comes to car stuff.  So it's good for you.  But don't take that too far - printing and eating it will probably make you sick.

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