Product Description
Interstate-McBee M-3973512 Oil Cap O-Ring Seal – 98.5–18 5.9L / 6.7L Cummins
Direct-replacement O-ring that seals the engine oil fill cap on late 5.9L and 6.7L Cummins B-series engines. Restores a proper seal to prevent dust intrusion and oil mist weep at the filler neck. Sold individually.
- Stops seepage: Fresh seal helps keep the fill neck clean and leak-free.
- Direct fit: Matches the OE profile for the factory oil cap.
- Durable: Built from high-quality elastomer for heat and oil resistance.
- Quick install: Swap in minutes during routine service.
Specifications
| Brand | Interstate-McBee |
| Part Number | M-3973512 |
| OEM Reference | Cummins 3973512 (oil cap O-ring) |
| Location | Engine oil filler cap |
| Sold As | Each (1 O-ring) |
What’s Included
- (1) Oil cap O-ring seal, P/N M-3973512
Vehicle Fitment
Verify by engine serial number (ESN) when possible.
- 5.9L Cummins: 1998.5–2002 (24-valve), 2003–2007
- 6.7L Cummins: 2007.5–2018
Install Notes
- Remove the oil cap, pick out the old O-ring, clean the groove, lightly oil the new O-ring, and seat it evenly.
- Do not stretch excessively; avoid sharp tools that may nick the seal.
- Inspect the cap and filler neck for damage or debris before reinstallation.
Recommended/Related Parts
- Replacement oil fill cap (if cracked or warped)
- Valve cover gasket set (if servicing for leaks)
- PCV/CCV service components as required
FAQ
How do I know this O-ring needs replacement?
Common signs include oil mist around the filler neck, dirt sticking to a damp area near the cap, or a flattened/hardened O-ring on inspection.
How many do I need?
One per oil fill cap. This listing is for a single O-ring.
Will it fit my 24-valve 5.9L?
Yes. It fits 1998.5–2002 24-valve 5.9L as well as 2003–2007 5.9L and 2007.5–2018 6.7L Cummins applications that use Cummins 3973512.
