The oil pressure gauge on your 1996 Geo Metro 1.3 is reading very low at idle yet jumps instantly to 30 when you accelerate is this from the gauge or oil pressure sensor or oil pump?

Answer 1

None of the above. When the oil warms up it becomes much thinner, more like water. Oil is pumped through the oil jourals to the babbit bearing surfaces. If everything is operating properly, the system is engineered to cause the bearing to float over the crankshaft on a film of pressurized oil. As the bearing wears, the clearance between the bearing and the crankshaft starts to increase, providing a space for pressurized oil to leak out. When enough oil leaks out, the oil pressure will start to drop. Right now, the oil pump is unable to provide enough volume of oil at low RPM, but the fact that it can still provide plenty of oil at higher RPM tells me that there really isn't anything wrong with the oil pump. You can raise the oil pressure and extend the life of the engine by using a heavier grade oil. The heavier (thicker) oil will not leak around the babbit bearings as fast, and as a result the oil pressure should go up. If you've been using a 5 W 15 oil, change to a 10 W 30 or even higher. If you've been using a 10 W 30, try a 15 W 50. Don't make too much of a change. Try small steps to see what the change is. Use the same BRAND of oil, just heavier grade, that way you won't introduce other potential problems. Good luck.