On these Toyota diesel engines, even a slight upward deviation of the needle from its normal position (usually just below the middle of the scale) indicates an overheating issue. In addition to all the cooling system causes mentioned above, one should not overlook excessively retarded injection timing, dripping injector nozzles, and elevated EGTs. These factors can also lead to overheating during prolonged highway driving (especially in hot weather with the A/C on), as well as to more serious consequences