Use the right type
Engine and coolant makers both warn against mixing coolant types. Use the type your manual names, and top up with the same.
Test it
Heavy-duty coolant guidance calls for testing freeze protection and condition, not just topping up. Test strips and refractometers are cheap.
Keep the stack clean
Radiators and charge air coolers clog with bugs and dirt, especially on rear-radiator motorhomes and trucks that tow in summer.
Where this comes from
- Detroit: Coolant requirements for engine cooling systems (PDF)
- Shell Rotella: Understanding engine coolant types
- ALS: Coolant formulation and cavitation
- Family RVing: Rear radiator cleaning
- Cummins: Motorhome quick reference guide, B6.7 / ISB (PDF)
Last reviewed 2026-10-19. General information only: your owner's manual and service information come first.