Sounds simple and perhaps the answer’s too obvious but the oil filter cap’s leaking on mine at 130k+ miles, oil, o-ring and filter change every 5K miles. The last 2 changes have revealed the cap’s leaking oil. I’ve checked torque and all’s good. Could it be faulty o-rings or is the cap failing or what else could it be?

 

jahummer, I would start with doing 2 things on your next oil change. The first being a cleaning of the groove where the oil filter sits and also the groove where the o-ring sits in the housing. Make sure those have no little chunks left or anything of the sort. Now that you have them clean, the second thing, look for any cracks, chips, grooves, any imperfections where the o-ring sits. If you need to, stress the housings, Put your thumbs inside the cap and try to pull it apart. Do that in multiple spots. Repeat with the housing. You could have a small crack.

If you find nothing here, then there is 1 last thing. How are you sliding the o-ring over the threads of the cap? I know this sounds like a stupid question, but this could be the cause of your issue. First things first, the o-ring should not be rolled (ie, in inside of the o-ring getting twisted so it becomes the outside and the outside the inside). This puts a lot of stress on the o-ring and this can lead to cracking of the o-ring. Kinda like if you are just pushing the o-ring down over the threads, you may be taking a chunk out of the o-ring (some imperfection in the threads) that is leaking to the leak. There are 2 ways that I recommend installing the o-rings for our caps. The first is to simply wrap the threads of the cap with some masking tape and then put on a little bit of old oil and use that to let the o-ring slide down over the masking tape, pushing down in several areas, making the the o-ring does not roll. Once the o-ring is in the proper place, remove the masking tape. There is a tool that you can get that has a little hook on the end that goes around about 270 degrees. Some people refer to it as an o-ring removal tool. In this case, you put the o-ring inside the hook and you rotate the tool around the cap, stretching the o-ring slightly as you pull the o-ring away from the cap and slide it down a thread or two and around and around you go until the o-ring is at the bottom in the groove. You can then stretch the o-ring slightly and pull the tool out. This works good for getting the old o-ring out too.

 

I've the appropriate pick for the O-ring, but not that careful when fitting a new one though not rough enough to damage it, IMO. I've been changing the filters for several years without issue, I reckon either the caps faulty, the last 2 o-rings are a bit off or it's my installation that's off. I've ordered a replacement cap which I'll fit on arrival. I'll also give the base threads a good cleaning.

 

I cleaned up everything, inspected all including the o-ring and will give it a run tomorrow. As I mentioned, this's the second filter replacement which's leaked. Curious, how much wobble does your filter have on the cap and how easy is it to pop off? I though previous ones required a good tug and didn't wobble. This one's quite loose, comes off quite easily and wobbles around a bit....

 

Had a short drive and it’s leaking just as much.

 

Fitted new cap, o-ring and filter. Perhaps a combination of issues. The new cap’s tighter fitting than the original, the o-ring, despite being only 3K miles old was flattened (may be normal, due to compression, I’ve never had a need to check) and the filter prongs which snap on the top of the cap were stretched out or defective which’s why it was loose and didn’t stay in place firmly (may not matter either). Had the same problem with the previous filter as well, but none of the prior to the last two ever had these issues so it may be a bad batch of filters.

Regardless, no more leak, just as it was for the previous 122K miles.

 

The o-ring should be compressed slightly. You don't want it flattened, but you do want it to be slightly oblong. This proves that the oring is under compression and providing a seal. Having an o-ring compressed too much can lead to leakage.