I've had my '02 C5 coupe now for 3 years without any major problems. The only major maintenance was having to change out the oil sender located behind the intake manifold. After assessing all of the posts here on the forum I decided to carefully make the cut above the sender and replace the component that way instead of doing major job of taking off the intake.

The new sender worked perfectly for a couple months but then I noticed that whenever I washed the car or it rained heavily I'd get erratic oil pressure readings. The pressure would all of a sudden go down to zero or up to 80 and everywhere in between.(Potential heart attacks were close when seeing the zero but since temp never increased I figured it was just the sender again.)

I put it on my list to check out the seal I'd put above the sender the next chance I got. After all, it only happened if it rained or I got a lot of water in that area while washing. Before I had a chance to do this however I got another zero reading while on the way to work and the temp gauge started to rise dramatically at the same time. I started to head to the side of the road before anything drastic happened when the pressure came back up to 40 and the temp started back down. I proceeded on to work while watching both gauges intently. The pressure would sometimes dip down to the 30's and one or twice hit zero again. The temp gauge was also behaving erratically going as high as 223 and then back down to 198.

Has anyone had this type of problem before? Is the temp gauge closely located to the sender and they could both be wet? How does the oil pump work on the C5; do they go out like this?
Any help would be greatly appreciated.