My '84 245 has almost 290,000 miles on the clock. The old b23 is still banging along, but I've noticed that over the last 100K the car has been getting more and more sluggish. I realize that we aren't talking about a high output engine here, but loaded dump trucks and school buses seem to take pleasure in out accelerating me. :-)

Was thinking that maybe the cam lobes are worn enough that they aren't opening the valves properly. Compression is about an even 150psi across all 4cylinders, and she only uses about 1/2 qt of oil every 3000mi. So the rings don't appear to be excessively worn (e.g. low compression). I'm actually surprised that the engine is in such good condition. I've ran it on 10w40 dino oil (Quaker State, then Castrol) all its life, and haven't always used the best filters. Up to this point, it hasn't required any work. Valves have been checked every 50K mi and I adjusted them at 100K and 250K. Also has gotten a new t-belt at 50/100/150/200/250k. Two waterpumps and front seals. That's it. One of the most reliable engines I have ever seen. An American V-6 might be faster and more economical in some applications, but it wouldn't make it to half this mileage without a major overhaul. Know several people with Fords/GM products that have done valve jobs and head work on well-maintained rigs <150K miles.

Anyway, "usual suspects" have been eliminated-i.e. cat convertor is about 3 years old and definitely not clogged, filters 'n fluids are recent, timing is OK, flame trap clean, etc.

How do I know when it might be time to rebuild?