I realized today I have a gap in filters. I realized it’s not clear how the filtered oil port is sealed from the unfiltered perimeter. Unfiltered oil is at pump pressure and it seems should leak past the threads into the center of the filter. Filter tubes don’t have o-ring’s or gaskets. How are the threads sealed from the perimeter?
how are port threads on the filtered side sealed
- Thread starter EE101
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Small dP at that threaded junction. Plus the threads are tight on each other which is going to seal the junction. If there's any leakage at all it's so small it wouldn't ever matter. If you're worried about it use some red loc-tite on the threads. 
First off I know you posted that in jest, but the last product you would want to use is a thread sealer as it rots out plastic within days, and in many cases RED Loctite items need torch heat to break it lose. A color to suggest in jest would be Loctite BLUE or PURPLE.Small dP at that threaded junction. Plus the threads are tight on each other which is going to seal the junction. If there's any leakage at all it's so small it wouldn't ever matter. If you're worried about it use some red loc-tite on the threads.
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^^^ Of course it's in jest, note the emojis. Go look up what an upside down smiley face means. Nobody with any common mechanical knowledge would use any kind of loc-tite or sealer on oil filter threads. Any leakage there, if any, is so small it's nothing to even think or worry about.
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Diesels are dealing with way higher fuel pressures than gas, so that would make sense on them having that gasket.
If a contaminant flows its way around and through all those threads to sneak past the filter element, it earned the right to embed itself in one of my rod bearings.
thats why I just coat the oil filter adapter in jbweld
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Agree it’s not passing tight threads at low differential …
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Sure, why Whip City like to count threads
I’ve actually recently wondered the same thing, but with the cartridge filter on our Carnival. On the cap end, it seals with a big fiber ring that presses into the cap. But on the inside, it looks like the picture. It just slides onto a circular metal piece inside the housing, no o-ring or anything. It’s a close fit, but it has to let some unfiltered oil past.
Not just higher pressures, but higher deltas also.
For reference, Cummins MCRS industrial engines are running fuel system pressures (on the pressure side filter) of up to 12 bar, with the nominal around 6.5-8 bar. The max delta is 300kPa.
In other words, the fuel *delta* is higher than many engine warm oil pressure!
Not to mention, fuel filtration on diesels these days is closer to 3 micron and is filtered in two stages where the *first* stage is ß>1000 at >7 micron. The second stage is even higher efficiency at even smaller particles. (ß>1000 >~4.5 microns). This is what it takes to get your ISO 4406 particle count below ISO 11 at >4 micron cutoff.
Given the much higher pressures, much higher deltas, and much finer filtration, it's no surprises that diesel fuel filters have a sealed thread spud. With the cakewalk that is lube oil filtration (by comparison), no secondary seal on the threads is necessary. You'll notice most Cummins spin-on fuel filters of recent vintage have the seal such that the threads are isolated on the dirty side. This is to ensure that the tiny bit of debris that can be generated when new threads are engaged will stay on the dirty side of the filter.
Diesel Fuel filtration is much more demanding than lube oil filtration-- by about an order of magnitude on particle sizes alone.
I’ve spent nearly 40 years in plumbing. IME, the threads on oil filters are pretty loose (I.e. loose tolerances). If they were just screwed together, they would leak pretty profusely. However, the compression of the gasket draws the threads together, minimizing any leakage. The threads will still leak without a seal or sealant, but I doubt that any significant particulate matter would make it through.
Also, as the delta across the filter goes up, the leakage would increase.
I looked at a Hastings and a Purolator Synthetic filter in my garage, and the Hastings had three threads; the Purolator had 4. Not much sealing area.
Now I’m intrigued.
Also, as the delta across the filter goes up, the leakage would increase.
I looked at a Hastings and a Purolator Synthetic filter in my garage, and the Hastings had three threads; the Purolator had 4. Not much sealing area.
Now I’m intrigued.
Look at the area and distance of leak path through the treads, and then the typically small dP across that connection. A leak volume can be calculated with a known oil viscosity and dP. Any leakage would be insignificant. It's not going to be anywhere close to a leaky leaf spring on an end cap of the filter.
Agreed. A tear in the media is also much more concerning. But this is BITOG. Hair splitting is encouraged.
That's getting into hair splitting even too much for me. Soon oil filers will be analyzed on the level of quantum physics.
A few wraps with teflon tape will suffice.If you're worried about it use some red loc-tite on the threads.
Lots of fuel filters actually use a square profile rubber washer in that junction, presumably to seal between the filter head and the top plate of the filter.
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