Could a small filter possibly do as good a job as a larger filter?

Dear Car Talk

Dear Car Talk | Mar 01, 1995

Dear Tom and Ray:

Toyota has reduced the size of oil filters for my 1986 Toyota Tercel and many other models to make removal easier in small engine compartments. They insist that the smaller size filters oil just as well as the previous larger size. But it seems to me that the physics of oil flow rushing through a filter at high speeds argues for using the larger filter, which is still available at independent parts dealers. What do you think?

RAY: Well, all things being equal, you're right that the a bigger filter should filter more oil. But, according to Toyota, all filters are not created equal.

TOM: Toyota reduced the size of these filters because owners and mechanics were tired of scraping skin off their knuckles everytime they tried to reach up into an engine and remove one of them. And what Toyota claims is that when they made the filters smaller, they also made them better.

RAY: The key is surface area. And one would presume that the bigger the inside of the filter, the more surface area there is to filter the oil. Well, Toyota says their smaller filter actually has MORE surface area than the bigger one it replaces. How? They say they've increased the surface area of the filter paper inside the filter by coming up with a new folding pattern. I think some engineer came up with the idea while sitting on the toilet one day reading Automotive News.

TOM: Presumably, there are deeper folds that there were before. Do we believe them? Why not. After all, these are the folks who brought us origami, right?

RAY: They also claim that the new filter paper they use has been improved so it filters smaller particles. And if that's true, that's also a benefit.

TOM: So I'd go with the smaller filter in this case, Mark. Your logic is correct, but it doesn't account for what's inside the filter.

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