Cure overheating under load (TD42 and others)

Symptoms

The fix, step by step

1. Clean the radiator core thoroughly.
2. Owners note that blocked internal tubes won't clear with a flush, so a recore or new radiator may be needed.
3. Refit or replace the foam seals between the condenser and radiator so air can't bypass the core.
4. Check the viscous fan clutch: when cold it should drag and spin only about half a turn.
5. Check that the underbody air dam and wheel-well rubbers are in place, especially on lifted trucks.
6. Fit a new thermostat and coolant at the correct mix.
7. Fit an EGT gauge and drive by it: drop from fifth to fourth when towing, and back off when temperatures climb past what you've learned is normal.
8. One ZD30 owner sees 300–450 °C at highway speed and about 600 °C on a long, steep climb.

Tools & part numbers

• Radiator brushes and fin comb
• coolant pressure tester
• EGT gauge

Where to buy the parts

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