I drive a 98 Bonneville, 15 miles to work and the other day the oil pressure dropped to 0 psi and the car stalled… a few hours later I went back to the car and checked the oil and it was full, but very thin. It did start and the pressure was back to normal (40 psi). But once it heats up the pressure drops again. I noticed the pressure goes up when I step on the gas. Only 2 months ago the head gasket and plenum blew and I had to have them both replaced. Did this have anything to do with this new problem and whan will it take to fix it?
It is normal for oil pressure to drop as the oil heats up and as the engine speed drops. However, what you need to determine is whether the oil pressure sensor is operating properly. It is a common point of failure. The best thing to do is hook up a manual gauge in place of the sending unit so the actual oil pressure under different conditions can be determined. The oil pump could be bad or the engine just plain worn out.
If the engine isn’t making strange noises, you may just want to replace the sending unit and see what happens.
When a head/intake manifold gasket fails coolant mixes with the oil. If this isn’t noticed right away, damage to the rod/main bearings can occur. This can result in low oil pressure.
Out of all the GM intake manifold gaskets I’ve replaced, about 50% of the engines failed shortly afterward because the owner operated the vehicle over an extended period of time with coolant mixed in with the oil.
Have an oil pressure test performed. And hope the bottom end of the engine wasn’t damaged when these gaskets failed.
Once you have determined the gauge is reading correctly, switching to 20w-50 oil may squeeze a few more miles out of the engine…