It will go all the way to the salvage yard... after you grandkids are your age, these engines are one of the best designed. With regular maintenance, the engine will outlive you.
Update: I have now owned this car for 3 years, and at 185,000 miles continue to appreciate it more. The ride is really not very rough as long as I don't drive quickly over rough roads or bumps. On smooth highway it feels like a much newer car. The exhaust pipe in front of the muffler rusted away, so I had it replaced and had the new one welded on (as the bolts were too rusted to remove). After that and today's oil change, the motor sounds as though it's purring like a kitten. A smooth pleasure to drive.
Surprisingly, there is no rust damage on the undercarriage or frame. I had it inspected today and the mechanic found no problems. The rust is only in certain spots on the body and exhaust, and looks worse than it really is.
Front brakes have close to 50% left, so should last another year. Heat and A/C show no indication of losing effectiveness.
This continues to be the best car I have owned.
That is great news about the rust. Some old Buicks - namely the LeSabre and Park Avenue, while being great cars overall, do tend to rust in important structural places. Perhaps the Century doesn't have this tendency.
Final comment from the owner.
My beloved Century lasted until January 2012 and 216,000 miles. Finally killed by rust and would not pass inspection. But an interesting story:
In December 2011 the car was in an accident when an Acura driver coming the opposite way crossed over the yellow line too far. He swiped my rear fender and ricocheted into the Hyundai behind me. They were both totaled, Buick had a minor dent in the rear, driver side fender. I ended up receiving over $900 dollars from the driver's insurance company and planned on spending that on new tires. Failed inspection the following month, but not related to the accident.
I put the insurance money, plus $350 from the junkyard toward my replacement car: 1986 Buick Riviera T-Type for $1700 (after taxes and fees). 83,000 miles, no rust, and tires that lasted another year. In all, I lucked out and I have been sold on the build quality of these old Buicks.
Another story about my Century. Once I was driving down the highway and heard a loud "CLUNK" in the engine bay. That was followed by electrical warning lights, overheating, and loss of power steering. I had the choice of pulling over to the side and calling for a tow, or driving the 20 miles, overheated, to my local mechanic. I took the risk and pulled it into the mechanic's lot at night, and left a note with instructions.
The water pump pulley broke off while driving. They replaced the water pump without a problem. There was no engine damage. After that, the engine would always leak antifreeze, but it never overheated.
If you need a reliable, affordable daily driver, and you get the chance to have one of these cars with low miles and without rust or major issues, jump on it.