I used to swipe a small film of new oil on the rubber gasket before installing my new oil filter. (Ford 4.6 liter) Then one time I saw my axle-grease can sitting there and decided to use that to lube the seal instead of engine oil. Mistake.
When I removed the filter 5K miles later the rubber seal stayed in place when I removed the old filter,…It was stuck to the mating surface on the engine. I found it when hot fresh oil began streaming onto my garage floor around the top of my newly installed spin-on filter when I started the motor. No more experiments with the oil filter for this guy T
The thread is continuously loaded in one direction, courtesy of that nicely compressed O-ring on top of the filter. No amount of thermal cycling is going to unseat the mating surfaces of each thread that got introduced to each other during installation.
The threads don’t form an actual seal, so there’s a tiny leak path through them from the upstream side of the filter to the downstream side. Unfiltered oil from the sump and pump will seep through there over the course of 6000 miles. That might add a tiny bit of resistance after you start unscrewing the filter, at which point any wear particles that settled in the thread gaps would have an opportunity to get jammed in the load-bearing area of the thread. If that were a significant factor, then I might expect the initial breakaway torque to be lower than the torque experienced just after breakaway. But I don’t think that’s what happens.
I think this is most likely. The threaded stem on the filter receiver is relatively small in diameter, whereas the O-ring is comparatively huge in diameter. A minor increase in drag force on the O-ring (caused by the installation lube being squeezed out and/or absorbed over 6K miles) results in a large increase in the torque required for removal.
And while we may never know for sure, I bet there are people at Ford, GM, and elsewhere who have done laboratory tests to figure out exactly where the increased breakaway torque on a 6000-mile-old filter is coming from.
And where to hang the filter to maximize the chances of burning your arm when trying to loosen it
While we’re at it, why is the drain plug on my car angled 45 degrees off of vertical, right on the edge of the oil pan? When you first get the plug out, the oil comes blasting out quite far to the side, so you put the catch basin over there. As the level drops, the stream slowly loses intensity and transitions to simply falling straight down out of the drain hole - and you damn well better be there to keep moving your catch basin so that it stays under the oil plume the whole time.
Well, it’s obvious I haven’t changed my own oil in a while; mea culpa. For what it is worth, I pulled out a filter and looked at the seal, and you are correct that it is a solid rectangular profile (not an actual O-ring, which has a round profile and is intended to be deformed under operation to assure sealing). Most of the seals I’ve been looking at lately have been for hot gas generators or igniters et al using deformable metallic or high temperature U-seals, and apparently that just got stuck in my head. You are also correct that the oil pump is just upstream of the filter; my only excuse there is that I’m typically looking at high pressure dynamic hydraulic systems where the filter is after the actuators to prevent lag or negative backpressure, which is obviously not really a problem with car engines. My errors.
Stranger
One other potential factor:
When you install a new oil filter, the O-ring is cold (room temperature). To prep for an oil change, the usual practice is to warm up the engine to operating temperature. This means that when you try to remove the old filter, its O-ring is hot/expanded and will be applying more preload between the engine and the filter, requiring more torque to loosen than the cold filter/O-ring you installed 6000 miles ago. The test for this is to try removing a used filter from a room-temperature engine. If that still has high breakaway torque despite being cold, then the thermal expansion of the O-ring isn’t a factor - in which case I’d fall back to @HoneyBadgerDC’s theory of the oil film being squeezed out of the O-ring/receiver interface and/or absorbed by the O-ring.
FWIW, here’s AutoZone’s answer to why oil filters get tighter/stuck with time:
I do agree that in most cases some degree of overtightening is present. In my shop we keep a record of who does the oil changes. Every now and then a mechanic will come storming into the shop wanting to know who did the last oil change. I will look it up and it will invariably be one of four guys who work full time on the service pit. I would regularly monitor their methods of tightening and other things they performed by just hanging out with them talking about something else while they worked. All the regular guys would go about 1/3 turn after making contact instead of 1/4 turn. Not a lot but enough to make some difference.
I haven’t changed my own oil in a long time, since I bought my current car from a dealership that offers free lifetime oil changes.
But I’ve changed the oil in cars I’ve owned dozens of times over the years. I always lubricated the gasket with oil because I was taught to and never knew why. It was just part of the “ritual”. I appreciate this thread for showing why that’s done. 
Loosening takes more torque then tightening on most things. Even freshly torqued bolts. Perhaps because there is less friction between moving surfaces than static surfaces.
Exactly. The coefficient of friction between two surfaces is higher when static than when dynamic. I remember that from my classes on Statics and Dynamics.
Informally termed
SDMB nitpick
- open oil filler cap (top of engine) to make the oil (in point 1.) flow out faster and flush more potential debris with it. Filler cap can be left sitting on opening so no dust etc… will get in there
Step -1: drove the car until the engine had reached operating temperature. The oil draining will then go a little faster, and drain more completely.
Did my Honda Element yesterday, nice hot oil ( I service 4-5 other cars around here)using a vacuum extractor, works well to avoid that first dump of oil when you loosen the plug. I thought they were a “new” idea, but I guess folks have been using them for years. And arguing whether oil is left behind. Some cars the tube cant be placed in an optimal spot, or cant navigate a bend in dipstick tube, (porsche boxster) which is where it is inserted so pulling the drain plug still neccesary. The Honda seemed to drain completely. And of course removing the oil filter.
Filter needed a wrench to budge free, as we all are discussing. Might have been able to get it off with rubber glove and easier access, but that “stiction” was there, as soon as it budged a little, spun right off.
Lubed up the gasket, then turned it till I felt it hit and then tightened about 1 full turn or so, then a little extra push…locations are often so difficult to reach that you dont have a lot of hand strength to overtighten. Im somewhat ancient too.
My plan to not make a mess of things failed though…reversing of extractor to put oil into recycling container popped off the hose, spraying oil around before I knew it. Next time I will use the pouring spout they suggest!!! Extractors are handy though, for fluid transfers, nice siphon pressure, beats the old turkey baster method.
Cool. Good to know. I wondered how well those extractors worked.