Cummins 3934373 — Genuine 180° Coolant Thermostat for 5.9L 12-Valve

MPN: 3934373  |  Also Known As: engine coolant thermostat, 180-degree thermostat  |  Service Note: Introduced by Cummins to reduce temperature-gauge cycling on ’94–’98.5 trucks while maintaining stock 180° operation.

Restore factory warm-up and operating temperature on your second-gen 5.9. This genuine Cummins 180° thermostat is a direct-fit OE part for 1994–1998 Ram 2500/3500 5.9L 12-valve. Built to Cummins specs for consistent regulation and long service life.

Features & Benefits

• OE 180° regulation for stable temps and proper emissions/performance.
• Direct-fit drop-in for 1994–1998 5.9L 12V (no modifications required).
• Updated response rate helps reduce temp-gauge cycling on some trucks.
• Durable wax element & seat for repeatable open/close cycles.
• Backed by Cummins quality and fitment.

Verified Fitment (Automotive)

Industrial/Off-Highway: Used primarily on B-series engines—verify by ESN for non-automotive applications.

Specifications

• Type: Engine coolant thermostat
• Nominal Temp: 180 °F
• OE Part Number: 3934373
• Quantity Required: 1 per engine

Often Paired With

• Thermostat O-ring (’94–’98): 3925466
• Thermostat housing cover gasket (’94–’98): 3933325 or 3927305 (verify by VIN/ESN)
• Fresh coolant: refill/bleed after service

What’s In The Box

• (1) Genuine Cummins 180° Thermostat (3934373)
• Seals/gaskets sold separately (see “Often Paired With”).

Installation Tips

• Drain coolant below thermostat level; clean housing surfaces.
• Install with the bleed/jiggle pin oriented up (if equipped); use new seals.
• Torque housing fasteners to spec; refill and bleed air from system.
• Verify opening behavior by monitoring coolant temp after warm-up.

FAQ

WILL THIS FIT MY 1994–1998 5.9L CUMMINS?

Yes—this OE 180° thermostat targets 1994–1998 Ram 2500/3500 5.9L 12-valve. Confirm by VIN/ESN if unsure.

WHAT SEALS/GASKETS DO I NEED?

Common pairings: 3925466 (thermostat O-ring) and 3933325 or 3927305 (housing cover gasket). Verify by VIN/ESN.

IS THIS DIFFERENT FROM 3928499?

Both are 180° units for ’94–’98. Cummins introduced 3934373 with a revised response rate to reduce gauge cycling on some trucks.

DOES THIS FIT 1989–1993 OR 24-VALVE/COMMON-RAIL?

No—1989–1993 typically use a different 180° thermostat (e.g., 5292738). 24-valve and common-rail engines use different parts.

IS THIS A GENUINE CUMMINS PART?

Yes—OE Cummins 3934373.