I have a 1990 Dodge Grand Caravan 3.3L with automatic, 230,000 miles. Blown head gasket (or cracked head, not sure which one) has been repaired with coolant block seal additive 30K miles before oil pressure problem started. The oil pressure problem is as follows; At idle oil pressure stays in good operating position. While driving at high speeds, the oil pressure decreases, and on decelerating the oil pressure will increase. Sometimes after warming up and at low speeds, the oil pressure will drop so low it lights the "check gauges" light and turns "check engine" light on but letting off the accelerator increases the oil pressure. Oil level is good with good oil. I use 10w40. The oil pan has a dent from hitting a curve, but that dent has been there for 6 years. Does anyone know why the oil pressure would decrease while driving then increase when decelerating?
williambailey
Odd, check the gauge sensor like it was recommended but, IIRC the light works on a different sensor. That dent in the pan is a suspect, over time the engine produces debris that stays in the pan, some of it is sucked by the oil intake screen wedging itself to the screen if in top of that the area of the screen has been reduced will be a matter of time before the pump can't pull enough oil to feed the engine at higher revs. than idle. Another possibility is that the oil pressure relief valve at the pump is either jammed open or the spring is broken or weak so at idle when the engine is not spewing a lot of oil the pump flows enough but above that the oil requirements are higher and might not be met by the pump system. Just for kicks I would change the oil filter first, it's easy and cheap and could be the problem, I doubt it, but I have been wrong before many times. Keep us posted
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