Why does does my oil pressure drop at idle after the engine temperature starts to reach 225 degrees F? At normal speeds the pressure is about 45-50 psi and at idle when hot its about 25 psi. When cold the pressure is the same as normal speed. The oil pressure at idle is fine if the engine temp did not exceed 210, once it goes past it, the pressure drops. 93 Jeep Grand Cherokee 4.0 I-6 Delo 400 15w-40 this occurs no matter what kind of oil you use, 5w-30 or thicker, dino or syn.