Hello, I purchased a new cat fuel water separator with the small oring or seal that goes on the threaded filter base. This is my third or fourth time breaking this oring over the years. Can anyone give me a replacement oring part number or alternative? Tired of throwing away filters due to not having the replacement orings.
CAT 256-8753 Seal
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by SIVRTNGE2, Feb 6, 2026.
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I assume yours is the metal can with a wire screen inside and a spring? That is the type @Big Road Skateboard is talking about I think, and yes do as he suggested by twisting the bolt.
If you give me your engine Ser. Number I can look it up again if you weren't able to find it in a search.Big Road Skateboard Thanks this. -
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Here is the number in the thread title. I thought these came with a new small o-ring around the bolt threads.
Hmmm - I can't post a picture off the website, but it is a typical screw-on type with a drain in the bottom.Last edited: Feb 6, 2026
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I just posted a picture of the actual filter. This is the primary filter that sits on the frame rail. I have broke 3 or 4 of the rubber seals that go on the filter base and had to pretty much throw the filters away because I couldn't get the oring. Im sure someone else has had this issue. I will also post a filter with the small oring attached to the drain valve.
Attached Files:
Oxbow Thanks this. -
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I’m still scratching my head on how you would rip the o-ring. Do you keep removing it and replacing the same one back on ? Did you lube the o-ring ? When I had my Cat, I never had any issues with o-rings.
Oxbow Thanks this. -
No, I remove the old one and replace it with the new one. I've had several to rip whilst trying to get it over the threads. I'm scratching my head too because I'm sure I'm not the only one that has had this happen. You must have that Midas touch. Please tell me what im doing wrong. I've been trucking as an owner operator with cat engines for 27 years. While this isn't an every fuel filter change occurrence. It has happened. Just trying to find the small replacement oring is all.
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I lube the o-ring, start on the bottom and just push it with the tip of my fingers and roll it up. Over the threads and all. I don’t stretch it to skip the threads(it will probably rip)Just let it do its thing as your push/rolling it slowly.Star Rider Thanks this.
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Thank you for the installation insight. I also do this. It seems to be more of a hassle during the winter months as this happened again a few days ago in Ohio at -6 degrees.
What i am looking for now is that little small o-ring seal or a part number so I can purchase some spares.
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