I have an '82 4000 with diesel motor. At high RPM the oil pressure idiot light comes on. Installed pressure guage and at an idle have 50 psi and at speed have over 80 psi (that's all the gauge will read). Oil and filter were changed about 1000 miles ago with no effect. Someone mentioned an oil pressure relief valve, but I can't find any reference to it in the manuals. Anyone have any ideas?
Thanks!
Tommy Cate