Last weekend I had taken out our 1992 Buick Roadmaster Estate Wagon to run some errands and to shake it down in preparation for driving to Pennsylvania in the coming weekend. I had noticed a problem with the oil pressure gauge: it would read normal pressure (20 psi at idle up to 45 psi or so when revved) but then would flutter occasionally, reading a much higher pressure (30 psi to maximum at over 60 psi). I was worried it was the oil pump but ruled it out for two reasons: if it were the pump, it would likely show low pressure and never high pressure, and the gauge was changing faster than it would be possible to do so (10 psi changes in a fraction of a second whereas a 10 psi change would ordinarily take a half-second or more).
I finally got out and checked under the hood. I figured the wire on the oil pressure sending unit was loose or broken — and when the engine vibrated, it would get loose and give those erroneous readings. Well I found the unit and went to wiggle the wire when it popped off in my hand. I figured it was some other sensor (like a block-temperature sensor perhaps) that just press-fit on. But when I cranked over the car, oil spurted out and the gauge read maximum. Indeed it was the oil pressure sensor, and it had been hanging on by a thread of rust.
I was very fortunate that it didn't break on the road because it would have dumped all the oil in a matter of minutes and I'd have to have it towed.
Unfortunately, that's not what happened.
Since it was back in the driveway I decided to just buy the replacement part and install it myself. Perusing the Internet offered little help, other than that the sending unit for this particular model required a gigantic deep-well 1-3/16" socket. I didn't have a socket big enough so I decided to go ahead and buy a new sending unit. I went to an auto parts store and they had a replacement unit on hand, but it took a 1-1/16" socket instead, and they didn't have one deep enough in-stock. They did have a 1-3/16" socket but I thought that maybe the replacement was the same size as the existing one even though they looked a little different in construction.
I hunted all around, stopping at 3 other auto parts stores. I finally found a socket that was deep enough at Sears so I bought that and headed back home. Naturally the original sending unit was 1-3/16" so I ran back out to the first store and bought their socket. Now I'm $50 into this project.
I got back home and tried to get to the sending unit from the hood-side, but there was just no way. I resigned myself to getting the jacks out and going in from the bottom. This was comparatively easy and I was done in 15 minutes. The car fired up with no oil leak and the pressure gauge read something close to normal. It did spook me on the trip, though, because it didn't seem to change — I was worried the replacement unit didn't have the right wiring and was falsely reading 40 psi. It started to work better as we continued so I think it's working okay.
So I think I would have been better off having it dump its oil in the middle of the road. I'd have had it towed, sat in some shop for an hour, and they would have replaced the sending unit — probably all at a cost of $200. The advantage would have been that I would have not had to fight last-minute holiday shoppers plugging up the roads and not spent 6 hours and not had my fingers freeze off in the cold.
I guess you win some and you lose some.