At 360k I'd be planning on some kind of a rebuild/replacement. Sure you can get more miles, but the motor will just keep losing power... Maybe pick up a junkyard head and start rebuilding that to swap in. It is going to need it at some point.

The other issue is the condition of the car around the motor. At 360k I'd think you'd have a lot of parts replaced by now. If not, you may lose the car before the motor. ???

Good luck.

500-750K would be a good estimate. The slow down in power could be lowered compression or worn valves, so a warm engine compression test will be needed for piece of mind.

Rejuvenating the head with valves, seats, guides and seals will be in your future. Not a terrible task, but save up for it and plan for a little down time.

Keep driving it regularly like it is a new car and it will last longer.

--
My back feels better when I sit in a Volvo seat

My '86 sedan that's in recycle heaven made it to 500K after an encounter with a magnolia tree. I had just had the head redone about 500 miles earlier due to a little bit of coolant in the oil. Before I pulled off everything I wanted/needed off it, including the head, I still got about $300 for it. I sure do miss it. Take care of it and treat it to regular oil changes and it will go and go.

A simple compression test and oil pressure test (preferably hot, while driving) can tell you almost everything you need to know about the current condition of the motor.

I have never run a B230 into really high miles (I had a B21 with 330K mile when the odo stopped and a B230ft with 280k miles) but there is no reason it should not be able to do another 100K miles.

That said, the cheapest was to hedge against impending doom is buy when you do not need it. A long block for one of these runs about $150-200. The machine work you should do if you are doing a full rebuild is about a $100 in my area. gaskets and bearings probably $150-200. Experience gained disassembling and re-assembling a motor...priceless. Then it is ready if something goes horribly wrong. Bonus experience if you pull it from a PnP and learn how the motor comes out.

Alternatively, a low mileage motor than you just inspect the bearings on, replace the oil pump and all the hard to get sensors could end up total...about $350.

When you NEED a motor and you do not have one already, you can double or triple most of these figures because that is how Murphy's Law works.

Certainly it couldn't hurt to put some $ away. At some point you may need it for a rebuild or replacement. But--if your oil pressure light goes out right away when starting up after an overnight rest (showing the pump works and the bearings are not so worn as to cause a delay in building pressure) AND - you're not burning oil or pushing it out through seals (showing your rings are doing their job) AND - your gas mileage is near what it has always been (showing it's not SO worn out)-----I'd not make it a major concern. Sleep well. -- Dave