First of all you should not be running to different shops. You don't run to a different doctor if you don't get the desired results on the first visit. Every new doctor and every new mechanic has to start over from the beginning and you're paying multiple times for the same diagnosis. Give the first shop a chance to correct any mistakes or to continue on with the diagnosis. With problems like yours it can be very time-consuming to eliminate the common causes and narrow it down to the less common ones. Rather than charge you for the many hours that can take, they often try the most likely suspect first and let YOU figure out if they need to go further. That is an attempt to save you money but it usually backfires because customers incorrectly think the mechanics don't know what they're doing. It's just like the doctor sending you home with a bottle of pills and instructions to "try these and see if they help".
The first shop may not be able to remove the new sending unit because electrical parts usually can't be returned, but they may have saved you an hour or two of labor already.
The next point of concern is if the second shop checked the oil pressure while the problem was acting up. If you had to leave the car there for hours until they could get to it, the engine and the oil would have cooled down and the oil would be thicker. That causes the pressure to go up for the first few minutes after starting the engine. If there's worn bearings in the engine the pressure will drop when the oil warms up and thins out.
There could also be an electrical problem such as the wire going to the sending unit is grounding out against the engine. You could prove that by disconnecting the plug from the sending unit. If the oil warning light still flickers, we know it's a wiring problem. That would not be common. From the way you described it, the sending unit would be a logical first suspect, and low oil pressure a close second.
Sunday, September 16th, 2012 AT 10:26 AM