My LS1 is overheating — do I need a new radiator?

Not necessarily. Speedway's advice is to rule out other causes before adding radiator rows:

Checklist before buying a bigger radiator (Speedway):

• A shroud that covers the whole core (the most common problem they see).
• Fans actually switching on at the right temperature.
• Water pump condition and flow.
• Air in the system — the LS thermostat sits low, so the steam line has to be plumbed to purge trapped air.
• Radiator fins not bent or blocked, and no internal damage.
• Ignition timing and air/fuel ratio.

First question: when does it run hot? At idle and low speed the fan does most of the work, so overheating in traffic points to airflow: the fan, the shroud, or the fan not switching on. At highway speed, moving air does most of the work, so if it's fine in traffic but hot at speed, look beyond the fan — radiator capacity, water pump, or the tune (Speedway's overheating guide makes the same split for race cars: hot under yellow = airflow; hot under green = look elsewhere).

If the radiator really is the limit (a thin stock core on a car making more power), a 2- or 3-row aluminum radiator is the usual step:

Core	Where it fits
1 row	Stock, light duty; the thin parts-store replacement
2 rows	Worthwhile even for stock engines; good for a performance car
3 rows	More capacity for real power; a thicker core
4 rows	Extreme heat: big power, boost with intercoolers, towing, racing