Product Description
Cummins 4327029 — Thermo Switch / Coolant Temperature Switch (3-Wire)
MPN: 4327029 | Also Known As: KSB thermo switch, temperature switch, coolant temp switch | Supersedes/Cross-Refs: 3920598, 3921642, 3408645
Why This Part
- ✓ OE thermal control for cold-start advance/KSB function on early 5.9L Cummins.
- ✓ Direct-fit 3-wire sensor with factory connector and thread.
- ✓ Restores proper cold-start and warm-up behavior.
- ✓ Genuine Cummins build for reliability and correct calibration.
Quick Specs
| Type | Coolant temperature switch (KSB/thermo switch), 3-wire |
|---|---|
| OE Part # | 4327029 |
| Supersedes | 3920598, 3921642, 3408645 |
| Qty Required | 1 per engine (sold individually) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1989–1993 | 5.9L 12-Valve (VE Pump) — KSB Thermo Switch | Dodge Ram 2500/3500 |
Industrial/Off-Highway: Used on select B3.9/5.9 Euro-2 B-Series and other ISB/QSB industrial applications — verify by ESN.
Often Paired With
- Thermostat & housing gasket (inspect/replace if removed)
- Coolant (drain/bleed per factory procedure after sensor replacement)
- Connector pigtail/repair if the original plug is brittle or damaged
What’s In The Box
- (1) Genuine Cummins Thermo Switch / Coolant Temperature Switch (4327029)
- Seals or adapters as required by application (varies; not always included)
Install Tips
- Disconnect battery. Drain coolant below sensor level to prevent spills.
- Clean threads/sealing surface. Torque to factory spec; do not overtighten.
- Refill/bleed cooling system; verify KSB/cold-start function on warm-up.
FAQ
WILL THIS FIT MY 1989–1993 5.9L 12-VALVE CUMMINS?Yes—this is the OE 3-wire KSB/cold-start thermo switch used on ’89–’93 5.9L 12V Dodge Rams (verify connector and thread before ordering).
WHAT NUMBERS DOES 4327029 REPLACE?Common superseded numbers include 3920598, 3921642, and 3408645.
IS THIS A SENSOR OR A SWITCH?It’s a temperature switch used to trigger KSB/cold-start advance circuits based on coolant temperature.
DOES TRANSMISSION TYPE MATTER?Some catalogs call out automatic-transmission trucks; function is primarily engine-side. Always verify by VIN/ESN and connector on your truck.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins 4327029 for proper calibration and reliability.
