Why does your 1992 Saturn sl2 oil pressure drop when the car gets hot?

Answer 1

The oil pump in ALL vehicles moves a specific volume of oil with every rotation of the engine. AS the engine runs faster, the pump moves more oil.

When the volume from the oil pump exceeds the rate that leaks past the bearings, pressure builds. Engines are equipped with a "bypass" valve that prevents the oil pressure from exceeding the engineered specifications; but when the space between the bearings and the crankshaft exceeds the original design specifications, the oil will leak past at a greater rate, and the oil pump will not be capable of maintaining the pressure that it once did.

In simple terms, as the engine bearings wear, the oil pressure will tend to drop.

Another part of the puzzle comes from the fact that the engine oil tends to have lower viscosity as it warms up. In other words, cool oil is thicker than hot oil.

When an engine wears to the point that the oil pressure starts to drop the way you describe, you have basically 3 choices:

1. ignore it. If the oil pressure doesn't drop to the point that the engine starts to "knock", you aren't doing much damage.

2. rebuild the engine. With new bearings the engine oil pressure will return to normal.

3. change to an engine oil that has a higher "viscosity". Whatever oil you've been using, use an oil by the same manufacturer but with higher numbers. If you've been using 5W-15, change to 10W-30 or perhaps even 15W-40. That should solve the problem unless the bearings are too worn.