I had always learned that you want to just hand-tighten oil filters on your car since it is metal on metal and you certainly do not want to strip any threads. I just heard that oil filters actually get tighter as they work which we all know is empirically correct since you need a wrench to take them off. My question is: what are the mechanics in the system that cause them to self-tighten?
Nope, there is a gasket on the oil filter. You don’t want to over tighten or the gasket may deform and allow a leak.
True but the threads themselves are metal on metal.
That’s not what causes the seal. And there are compression limiters built into the filter to keep you from deforming the seal and causing the threads to be damaged. Unless of course you used some mechanical advantage type wrench to over torque it down and crush the filter.
I get all that. The question on the floor is how do the filters tighten themselves?
When oil contacts the inner ring of the seal, it expands a little more. My dad used to run a ring of oil around the ring for this purpose.
They don’t “tighten themselves”. Expansion and contraction from heating/cooling make a change over time. How many hot/.cold cycles does an engine (and hence the oil filter/oil filster mount) go through between 3k, 4k, 5k nile oil changes? And sometimes you have dissimilar metals galling that takes place - steel to stainless, steel to aluminum, stainless to steel or aluminum (worst case).
I thought the question on the floor was if they do it?
I presume they do since you need more torque to get one off than it was put on with.
The threads may fill with crud and the gasket could get sticky as the oil and rubber degrade slightly. Really, all kinds of reasons.
Have you noticed that jars of food are often much more difficult to open after you close them? Same basic deal.
As someone who has done hundreds of oil changes, I think this is the correct answer. For whatever reason, the seal sticks “better” to the engine as time goes on. I am not exactly sure why this is the case, but am guessing it has something to do with heat and the material properties of the seal.
I always hand-tightened my filters, with a little oil smeared on the rubber gasket. Once the rubber gasket makes contact with the metal, I turned the filter about a half turn. Never too tight.
The filters never tightened themselves. When it was time for the next change, the filter came off readily by hand.
I have a theory on this , I will never know if I am right or wrong. When we install the filter it is well lubricated I beieve the lubrication is mostly squeezed out and what remains is possibly absorbed by the gasket making it tighter. My shop would change close to 100 filters per day and I would often get called over when they could not get one broke loose.
They don’t. Simple answer, flawed question.
It is not a flawed question, they do get tighter. It was not unusual to install a cheater on the end of the oil filter wrench just to break it loose.
I don’t understand this - most threads are metal on metal. What are you seeing as different here?
That if you strip threads on the oil filter, you’re screwed
I’m not an expert, but I understand that it’s possible for one set of threads to be a different metal from the other set, which if I understand correctly can cause troubles in automotive applications.
IMHO, the average DIYer is 10x as likely to strip the oil drain plug as the oil filter threads. Before the filter gets tight enough to strip the threads, the can would have started to collapse. As for the drain plug - the inane reliance on crush-washers means that the plug needs to be tightened pretty snugly. But, too much is going to be a problem. I always install a Fumoto 1/4-turn drain valve on my first oil change, to make life easier.
Changed my oil today. Torque wrench. 29 ft-lb.