Practical Advice on Filter Post-mortems

Some service technicians routinely cut open spent filters to perform a visual analysis. This makes sense in some cases, but not in others.

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Some service technicians make it a standard practice to cut open spent filters to perform a visual analysis of their contents. This makes sense in some cases, but not in others.

"If you are prematurely plugging fuel filters, you certainly want to cut them open and look at them," says Paul Bandoly, WIX Filters. "Cutting it open can give you an indication of what's going on and what you need to do with your fuel supply."

For example, if the filter media is black, shiny and covered in a thick, tarry-looking substance, it can signal that the fuel is degrading and oxidizing. Media that has a slimy, smelly coating and a dark olive green coloration could indicate a biological contaminant in the fuel. "If you cut the filter open and the media is swollen and looks like you just took it out of a bucket of water, you obviously have a water problem," says Bandoly. "Sometimes, cutting the fuel filter open can be helpful as a diagnostic."

Bandoly also recommends cutting open coolant filters at every filter change. "Things that can go wrong quickly with coolant are visible," he states. For example, you will be able to see contaminants such as dirt or rust trapped in the media. "Because coolant filters are bypass filters, the slow flow through the coolant filter allows sedimentation, rust and chemicals to precipitate out.

"All by-products of improper coolant system maintenance will surface and be visible in that filter," he continues. This includes improper matching of coolant and the inhibitor package. "Even in the best of fleets, there will be somebody who will try to buy the best products and won't know whether they go together."

Take an organic acid coolant and a traditional inhibitor package. "They can conflict with each other and the chemicals can become unstable. It may cause gelation," Bandoly explains. "I've had [filters] come in here weighing four to five times their original weight and they're just packed with gel. So as a matter of routine maintenance, it's not a bad idea to cut open the filter."

The same can't be said for oil filters, however. "If you cut open an oil filter and see something, your component has probably already failed," Bandoly asserts. Because oil filters are designed to trap very minute particles, contaminants are largely invisible to the naked eye. "If you cut open a filter... the only thing this will do is destroy the filter condition and verify something failed."

Also avoid cutting open filters of any kind if you plan to seek assistance in diagnosing filtration problems. "If you want a filter manufacturer's help, leave the filter alone - don't alter it," Bandoly advises. Opening it up will only introduce more contaminants and make diagnosis more difficult. "So leave it intact as it was removed from the vehicle