Fuel filter small square cut gasket.

[SheldonBates]

Some info I thought might be of interest and/or helpful to others. The first time I changed the fuel filter on my '96 CTD I wondered what the small square cut gasket was for that was included with the filter along with the regular round o-ring for the WIF sensor. None of the spin-on oil or fuel filters I have worked with through the years have had the extra square cut gasket. (The fuel filter I used for that first change was a WIX 33402 which is the correct cross for the Fleetguard FS1253 which I now use. )



After several attempts I was unable to get an answer from Fleetguard so I tried WIX. The WIX Catalog Department did reply to my e-mail. Their response was: "The square cut gasket goes on the threaded stud. The purpose of the gasket is to stop already cleaned fuel from being contaminated by dirty fuel when the engine is off. Not all filters require a clean side gasket but if the filter does require it, it is not a good idea to leave it out. Also, if a filter does not require the gasket adding it could stop the outer gasket from sealing correctly. [WIX] 33402 does require the gasket, please do not leave it out when you install the filter. This gasket is called a thread seal gasket. " A very good explanation I felt.



Those that have worked with standard straight threaded joints (non pipe thread) know that they are not liquid tight by themselves. I believe all spin-on filter applications - oil, fuel, etc. - use a standard straight thread for the base nipple (stud) and therefore would seem to be open to the chance for cross contamination from the "dirty" side to the clean side when the engine is off (or running for that matter?). I find it curious and still wonder why the FS1253 (also upgrade FS19519) and WIX 33402 seem to be, in this application, the only filters that are concerned with a thread seal gasket.



Anyone else have any thoughts or additional info?

 

[Shadrach]

FYI Fleetguard uses that type of small quad ring on the threaded stud for a lot of their fuel filters, 89-93 & 94-96 Dodge, as well as the bigger engines too. They have done this for decades. David

 

[AEdelheit]

Majority of the fuel filters I change on Fiat diesels have squared edge O ring that goes over the threads, same concept

 

[MLee]

Someone asked a while back if it was necessary to change this quad gasket each time the filter was changed. the consensus was a yes, it should be done, thats why its in the package. Other manufactures, who knows.

 

[SheldonBates]

Thanks Shadrach, AEdelheit, Mlee for your replys. I wasn't aware that the thread sealing quad ring was so commonplace. I still find it curious though that they are only used on certain filters. It would seem that any spin-on filter would want the additional thread sealing. Anyway, thanks again for your responses. Shel