Product Description
MAHLE C31421 is a molded-rubber coolant thermostat gasket for the 1989–1998 5.9L Cummins. It seals the thermostat to the housing to prevent leaks and maintain stable operating temps. Built to OE specifications for reliable fit and longevity.
- Application: 5.9L Cummins (12-valve) 1989–1998
- Construction: Molded rubber, OE-equivalent materials
- Function: Seals thermostat to housing; helps prevent coolant seepage
- Warranty: Manufacturer’s limited (per supplier terms)
Fitment
- 1989–1993 Dodge D/W 250 & 350 with 5.9L Cummins (12V)
- 1994–1998 Dodge Ram 2500 & 3500 with 5.9L Cummins (12V)
Cross Reference Numbers
- Cummins: 3923331
- Other refs (industry listings): 8350 6402, 4728 207
- GTIN/UPC: 757522711272
What’s Included
(1) Thermostat housing gasket (C31421). Thermostat not included.
Install Notes
- Clean mating surfaces; inspect housing for pitting/warpage.
- Follow torque specs; do not over-tighten the housing bolts.
- Top off coolant and bleed air per service manual.
FAQ
Will this fit my 1989–1998 5.9L Cummins?
Yes. It fits 12-valve 5.9L Cummins in 1989–1998 Dodge 250/350 & Ram 2500/3500.
Is the gasket rubber or paper?
Molded rubber design for durability and sealing performance.
Do I need sealant?
Generally no—install dry unless your service manual specifies otherwise.
What thermostat does this pair with?
Any OE-style 5.9L Cummins thermostat (e.g., 180°). Verify year/engine before ordering.
