No smaller oring on oil filters?

[The motor guy]

So on spin on water separating fuel filters, they have a little 3/4" gasket that goes onto the threaded fitting where you thread the filter onto. Funny how this occurred to me on my boat that I installed a racor filter on and didn't know what that smaller gasket was supposed to be for until a few days ago when i changed the diesel fuel filters on my fass lift pump on my cummins. My guess is its to keep water on the dirty side of the filter where it belongs. Now, with that being said why don't they do the same on oil filters to prevent cross contamination of oil? As much as everyone gets bent out of shape about leaky filters. (Fram) I figured id throw another wrench into the mix here.

 

[HighHy21]

oil doesn't usually contain enough moisture that needs to be separated, like what's inherent in diesel fuel.

 

[The motor guy]

oil doesn't usually contain enough moisture that needs to be separated, like what's inherent in diesel fuel.

True, but there isn't anything stopping the oil from leaking through the threads to the center section before it gets filtered

 

[johnmyster]

It's been discussed before. See this thread where we again confirmed that Zee06 can't detect sarcasm.

What about the threads?

Water separating fuel filters are often before the pump, so they're under suction...and where air bubbles go/accumulate matters as a function of pump cavitation. Your lift pump sucks through the first filter and will loose prime if a big air pocket accumulates at the top of the filter and goes to the pump on startup.

The other aspect is that oil pumps tend to recirculate and "polish" the sump. A small bypass ratio isn't catastrophic. HP fuel systems, we don't want bypass.

 

[ZeeOSix]

That thread got locked because of "technical bickering" ... but isn't BITOG about the technical details instead of becoming a social "Facebook" hangout site, lol

Anyway, in that thread I did a calculation in post 27 (shown below) that showed even with 16 PSI of dP across the threaded mounting spud that the leakage of oill from the dirty side through the threads is very insignificant.

"I just so happened to run some numbers through the dP calculator tool for a narrow long flow path that a non-tapered threaded joint "spiral leak" would create. If the dP across the threads was 16 PSI, the leak rate through the spiral leak path would be around 0.02 oz/min (0.00015 GPM). If there is a 16 PSI dP across a typical oil filter, it's going to be flowing at least 8-10 GPM. So the leakage through the threads compared to the total flow through the filter would be around 0.00015/8 = 0.001875% of the total flow. Better get out the thread sealant. "