Chrysler Repair: 1999 Ram 1500 4x4 Sport 318, oil pressure gauge, degree thermostat

Question
my truck sat untouched for two years. It ran perfect when I stored it....my oil pressure drops from 55 lbs to 30 lbs after about 40 minutes on freeway.. It stays at 30 even when I come to a stop...you would think that it should drop lower at idle...if I stop and quickly restart the truck, it will go back to 55lbs and be fine for a while..I have changed the sending unit, and cleaned out the pan which had some sludge in the bottom, and put in a high volume melling oil pump.. I also have a 160 degree thermostat..do you think it could be a computer problem, because of the thermostat? I'm worried to drive the truck because I feel that 30 lbs is way too low.. I would really appreciate some help

Answer
Hi Behr,
I wonder if the oil pressure gauge or the wiring to it may be fouled up. Why not actually use a gauge at the sending unit to see what sort of pressure you have. It should be 8 psi at idle, and 30-70 at 2,000 rpm according to a manual that I have for the 318 from the '80's. Also check the resistance of the sender to see if it is changing between idle and 2,000 rpm in such a slight degree when the engine is warmed up. If it is changing alot, rather than not at all the way it appears on the dash, then I would check the wiring to the dash. I don't have any truk manuals so I can't be sure whether the signal is digitized at the pcm and sent on the data bus to the cluster or if it is a conventional resistive circuit to an analog gauge at the dash, because I don't have any truck manuals.
Roland
PS I just found your question in the pool to which it had been referred.