Originally Posted By: 440Magnum
Originally Posted By: NJC
I'm speculating here - but the problem could be weak media (numerous failures are possible) or lacking pitch uniformity at media to end cap bond. I haven't studied other filter designs enough to know if this is typical, but it looks like the pleats are too tight for majority of glue joint, and too wide near seam.
I agree with ZeeO that this is the best working theory. Where the theory comes apart a little (pun intended) is that if pleat uniformity were the only factor, then EVERY entry-level Fram-built filter (Orange can and clones) would do this, because they are far more wide-pleated in places than a Purolator Classic. Just speculating here, but maybe the Fram Orange Can's end caps made of filter media actually save it. Maybe its the stress of a flexible medium glued to a rigid metal end cap. Or maybe its the Classic media is softer than the cheapy Fram media.
I dont' think its just one cause, its at least two or more contributing factors coming together.
I think this is the correct, multiple causes. If I had to hazard a guess and pick a culprit, I'd go with weakened media. Not necessarily too thin (as per pictures above, the media from Bosch 3330 measure .6mm or .024") but too weak - either weak design or batch, or weakened with oil saturation .. or another explanation. I did a quick glance through this gentleman's PDF, and he compares Corolla filters but also has media measurements - they seem to vary between .021" and .038" so the .024" I observed is well within the range.
http://www.corolland.com/oil-filters.html
Originally Posted By: 440Magnum
And its shtuff like this that is driving me to pay the premium for synthetic wire-backed filters for EVERY vehicle at the moment.
Myself included, I'll go for a different MFG like Wix. But gauging from other's observations, Purolator filters are VERY popular which means this problem is widespread. And it's significant.
I won't do business with companies that produce substandard product, and it should be shouted from the roof tops until something changes.