BASIC TROUBLESHOOTING 112 All information subject to change without notice. DDC-SVC-MAN-0039 Copyright © 2009 DETROIT DIESEL CORPORATION Abnormal Coolant Temperature Symptoms and Probable Causes Probable Causes Above Normal Below Normal Restricted cooling system passages X — Restricted radiator core passages X — Slipping fan drive belts X — Faulty temperature-controlled fan X — Obstruction in front of radiator or intercooler X Low coolant level X — Damaged hoses X — Faulty thermostats X — Faulty water pump X — Faulty radiator pressure cap X — Air in coolant X — Thermostats not fully closed — X Leakage around thermostat seals — X Faulty temperature-controlled fan — X