Auto Service World
Feature   October 1, 2004   by Jim Anderton

First Rate Filtration

What makes a good oil filter? The right ratings can help you decide what's right for you and your customers.

There’s little in automotive service that’s as ubiquitous as the oil filter. Most technicians have handled hundreds of the slippery cans before they begin their apprenticeships, and as a result, they’ve become a “no-brainer” part choice for many shops. You can install what the jobber has on sale this week, but a little thought can yield better engine protection for your customers and better margins for you.

Oil Filter Ratings

The original method of rating a filter was the technique borrowed from the hydraulic and heavy-duty industries: micron ratings. A micron is another name for micrometer (one millionth of a meter or 39 millionths of an inch). The numerical value associated with micron ratings describes the size of the smallest particle that a flat sheet of filter paper or “media” will stop. It’s intuitively a good indication of how porous the filter media is, but it’s usefulness stops there for automotive applications. The first problem is that different manufacturers use different test methods, limiting the micron rating to comparison within the same manufacturer’s filters. That can be useful if you’re only ever using a single brand, but if the idea is to find the best filter, the numbers can be wildly misleading. There’s no basis for comparison. Another issue is that micron testing uses a flat sheet of filter media and automotive oil filters are anything but flat. The physical construction of the filter matters, as does the amount and type of media inside the can. The fluid being filtered also has an effect, and again, there is no way to compare test results across brands. In automotive engines, contaminants aren’t simple suspended particles of grit. Fuel, coolant, condensation and gasketing material residue can play a part, something bench testing can’t duplicate across brands. The whole filter must be tested, not just the media. The size of the particles that an oil filter can pass does matter, but micron ratings are best left for hydraulics.

If micron ratings don’t work, what does? Single-pass and multi-pass efficiency ratings are a better way to determine filter performance. The Single Pass test flows test oil seeded with tiny particles of a controlled size, like glass beads, through the filter. The post-filtered oil is examined and the efficiency of the filter is expressed as a percent. A single pass rating of 85 percent, for example, filtered 85 percent of the test contaminant in a single trip through the filter. The key factor in comparing filters using single pass numbers is that the size of the test contaminant particles matters. 95 percent efficient sounds great, but 95 percent of what? It’s important to know the size of the filtered particles for a true test. Single pass efficiency testing is far better than micron ratings because it uses a real filter under a simulation of circulating oil in an engine. In a real engine, however, filtering is a little more complicated than the test bench scenario. Filtering happens in two ways. Contaminants can be stuck on the surface of the filter media (adsorption) or can be trapped by the tangle of fibres inside the media. The oil, however, keeps flowing as long as the engine is running, and can drive trapped particles through the media and back into the engine, lessening efficiency. On the other hand, adsorbed particles on the filter paper surface can block further contaminants, or slow them down enough to be trapped by the filter, increasing efficiency.

The solution may be at hand, in the form of a standardized multi-pass test methodology backed by major associations like the SAE, ASTM and ISO. Multi-pass testing is superior for several reasons. The first is that it’s repeatable, using industry standard equipment and methods, allowing comparison between manufacturer’s products. Like single pass testing, it’s better than micron rating because it tests the whole filter, not just a flat sheet of media. And best of all, it accounts for the aging of the filter over time, just like in a real engine. The test works by injecting contaminants into the oil stream while sampling both before and after the filter at regular intervals. The test stops when a predetermined pressure drop is reached. The results are expressed as the “B ratio”. B ratio is defined as the number of particles greater than a given size in the fluid upstream of the filter, divided by the number of particles of the same size found downstream of the filter. Particle numbers are determined by count, not weight. A B10 value of 2 would mean that for every 1,000 particles greater than 10 microns found upstream, 500 particles greater than 10 microns passed though the filter. Since only half of the particles are removed, a B10 value of 2 indicates that the filter is 50% efficient for taking out particles larger than 10-microns.

That’s a good indicator for 10-micron particles, but other B values are possible, and meaningful by using different particle sizes. That’s important because particles of different sizes produce different wear characteristics.

The biggest problem in adopting B-testing will be the time it takes to perform the test. At 12 hours for a conventional test, or four for the fastest automatic machines, it will takes years to test every one of the thousands of different filters in each manufacturer’s catalog.

Expect the heavy-duty industry to benefit first from the new system. In the meantime, single pass efficiency will give an accurate indication of the benefits of going up to premium filters within a manufacturer’s offerings. For the name-brand players, there’s a definite advantage to better oil filters. Selling that advantage will still require some savvy at the service advisor’s desk, but some apples-to-apples performance data, even within a brand can help. Premiums are better for your customers’ engines and better for your bottom line, but you must face the customer interrogation first. Fortunately, because better oil filters deliver, it’s the whole truth, and nothing but the truth.

The profit perspective

Successful independent businesses know that running a good shop means differentiating their service from quick-fit operations and “speedy lubes”. One way is to offer premium oil change options, including upscale filters. Peg Campbelton, director of marketing for Honeywell Consumer Products Group (Fram) declares, “Premium filters give additional benefits. The underlying reason for selling premium filters is that the market is a mature market. The likelihood of selling more filters is slim. To offer opportunity for growth, premium products play a part. The units (oil filters) have declined about 2% per year, so for our customer the opportunity for growth comes from the filters you sell now. It’s an opportunity for growth. Bring the customer something of value.” Fram uses a ‘good better best” product lineup, with good model coverage without excessive inventory. According to Campbelton, long drain oils are a good “hook” when upselling premium oil filters. “The benefit is high capacity, ultra high capacity. For synthetic oils, upsell to a filter that can match the oil’s drain interval.”

B-ratios are the future of filter rating

B-ratios will be the most useful performance rating yet, when fully adopted, but the numbers can be confusing. Numbers higher than 75 give little additional performance, and can be safely disregarded. That’s because for B ratios of 75 and higher, there are not enough particles in downstream liquid samples to make counting them statistically significant.

B-ratios are the future of filter rating B Values and Corresponding Efficiency Levels

B-Value Percent Efficiency
1.00.0% Efficient
1.216.67% Efficient
1.533.33% Efficient
2.050.00% Efficient
3.066.67% Efficient
4.075.00% Efficient
16.093.75% Efficient
20.095.00% Efficient
50.098.00% Efficient
75.098.67% Efficient

The engineering perspective

What’s in a premium versus a “white box” filter? According to Gary Purser, Technical Services Manager for Wix Filters, “Filtration media has come a long way. It’s a balance of cost and performance. It varies depending on the engine. Premium filters do a great job, but “white box” is all over the board depending on who made it. You get a lower grade of media and less quantity of media. Less media means less area for the oil to flow through and if the media goes too fast, the oil can blow right through it.”

Purser notes that efficiency is just one part of the filtration equation. “There seems to be a lot of confusion about what filters can and can’t do. There are a lot of other issues besides the oil. Stop and go driving gets moisture build up in the crankcase. Enough moisture in the cellulose media can cause swelling that can make the media restrictive. It’s critical to avoid restriction or plugging. And white box filters tend to be mostly cellulose. If they plug, and you have a strong, say, 30-pound oil pressure relief spring you’re in trouble.”

Purser’s warning is especially important in Canada, where cold weather starting can add “impulse fatigue” to the difficulties facing the oil filter. Impulse fatigue is caused by the momentary overpressure the filter sees from cold oil at startup, and it’s enough to damage the media or even the filter’s seals. White box can be risky in the cold.

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