Two stories, both involving Volvos. I like old Volvos, BTW.

First was when I was a teenager (mid 80's). I had an old 1963 Volvo 122 that I'd bought for $450. It had a lot of miles. I put a bunch more on it, at some point the engine got a bit tired. It was summer, I didn't have much else to do (lived in the country) so I took it out and rebuilt it. Did a really good job. Had the block bored, got new oversized pistons. Rebuilt the head. Crank sized/turned/polished, new rods&mains. New oil pump. New gaskets. GOOD AS NEW!!! I reinstalled the engine, added fluids, and cranked it up. It started up and ran perfectly on the first try. I let it warm up, no leaks, no problems. Turned it off, went to restart it and noticed that the oil pressure warning light didn't come on. Hmmm... I looked and no big deal, the wire had fallen off. The sensor is tucked in behind the exhaust manifold, which was scorching hot. I tried to push the connector back on and burned my hand. And I noticed the connector was a little 'sprung' and not holding as tightly as it should. Anyhow, to make a rambling sotry a bit shorter, I got antsy to take it on a test drive, I didn't fix the oil warning light wire any better, and took off on a drive. And about 10 miles later it started to lose power, make a bit of noise. I pulled over and turned it off. Tried to restart it, starter clunked but the motor wouldn't budge. Opened the hood and heat was BAKING off the block, more than normal. And the oil warning light wire was unhooked. I checked the dipstick..... BONE DRY. And I looked underneath and saw that the oil drain plug was missing. Apparently somewhere along the long rebuild process I'd replaced it finger tight, and when I reassembled it I never tightened it. And it wiggled out, and in conjunction with the loose oil warning light wire.... Yeah, pretty much had to start over from scratch, totally different motor sourced from a junkyard.

The second story of woe: I now have a 1993 Volvo 245 wagon. That I keep making faster. And faster. Until reliability is a bit of an 'issue' (I'm about 97% through a turbo LS swap on it right now). Anyhow, this was when it still had the 2.3L 4 cylinder, with a 4 valve DOHC swapped on it, and a big turbo. It made about 300-ish hp at the rear wheels. In an exciting light-switch manner that small engines with big turbos have. Anyhow, one of the side effects of running a lot of boost was that headgasket life was getting iffy. I use Cometic MLS gaskets, but they still only seemed to last 5 - 10K miles at a time. So I had what I thought was a bad HG, it was starting to push coolant at full boost (24 psi), gradually getting worse, until one day it started to fog out the tailpipe pretty bad so I pulled it apart. And found that it was a bit worse than just a HG, the forged pistons were looking a bit ragged on their tops (detonation). So I pulled the bottom end out and took it apart, discovering ent top ring lands and broken top piston rings. So the rebuild project got bigger - I got new pistons, balanced them, gapped the rings, put it all back together again with a new HG. And on the first start up? Fogging the area again. Massive amount of coolant coming out of the tailpipe. Plugs indicated a major issue with #4. WTF??? I tried eliminating things that were easy. It had good compression, no coolant in the intake, nothing. Stumped, I took it apart again, and discovered it hadn't been a HG the first time around - it was a split way down low in the cylinder bore. that I'd never noticed while the engine was completely apart. I had to start over from scratch on that as well, another junkyard motor stripped down completely, taken to the machine shop for work, built up from a bare block. So yeah, done twice.