Detailed guide for SPN 111 FMI 18
Back to top ↑Engines that never warm up soot up faster. In winter climates, this quietly creates aftertreatment headaches later.
Jump to
Share ↓SPN 111 FMI 18Severity: Info
SPN 111 FMI 18: Coolant temperature below normal – thermostat stuck open
Quick Answer
Coolant temperature below normal – thermostat stuck open
Code
SPN 111 FMI 18
Severity
Info
Applies to
Check OEM application
Can I drive?
Driving suitability is not established by this code alone.
Common Symptoms
- Takes forever to warm up
- Cab heat weak
- More soot/more regens
Likely Causes
- Thermostat stuck open
- Temp sensor drift
Common Fixes
- Replace thermostat
- Verify sensor readings vs actual
Full technical sections↓
What does SPN 111 FMI 18 mean?
Back to top ↑Coolant temperature below normal – thermostat stuck open
Video walkthrough for SPN 111 FMI 18
The videos below are embedded using YouTube’s official player. We do not host or claim ownership of this content. Use it as a visual reference and always confirm with diagnostics for your exact truck configuration.
Cascadia fault code SPN 111 FMI 1/18. Coolant level low. DIY coolant sensor replacement & new plug.
Channel: Carlos Diesel Electric Pedro Fuentes • View in BigRigFaults Media • YouTube source
If a creator disables embedding, the video will stop showing here. That’s normal and it’s their right.
BigRigFaults Community
Community discussions related to SPN 111 FMI 18
Compare symptoms, repairs and real-world experience from drivers, technicians and owner-operators.
Fault Codes / SPN / FMI
SPN 1590 FMI 19 - Meaning, Causes & Diagnostic Discussion
0 replies7 views
Fault Codes / SPN / FMI
SPN 4077 FMI 14 - Meaning, Causes & Diagnostic Discussion
0 replies11 views
Fault Codes / SPN / FMI
SPN 84 FMI 21 - Meaning, Causes & Diagnostic Discussion
0 replies8 views
Fault Codes / SPN / FMI
SPN 1071 FMI 5 - Meaning, Causes & Diagnostic Discussion
0 replies7 views
Still stuck with SPN 111 FMI 18?
Ask the community and include your truck year, make, engine, active codes, symptoms and recent repairs so people can give useful answers instead of performing mechanical astrology.
Ask the Community →Related fault codes
No related faults found yet.
Mechanic community notes for SPN 111 FMI 18
Back to top ↑Real-world tips from technicians. Submissions are moderated to keep spam and “my cousin fixed it with duct tape” content out.
Share your fix / advice
Keep it useful: symptoms, what you checked, what fixed it, and whether the code stayed inactive after a drive cycle.