Assuming that you'll want a second opinion after reading responses here so far, I just want to note that I'm hoping you're NOT driving this car now with the oil pressure light on? No sense in doing more possible damage.

If you still have some of the oil which was in the engine, send a sample to a lab and see if there are any evident problems.

You can find someone with the equipment to do an engine flush. If you can't find one, then get some AMSOIL or BG engine flush and do it yourself.

Then fill the engine with a good synthetic engine oil. Run it for at least 1000 miles, and send a sample to the lab.

If you have antifreeze in the oil, the oil will sludge very quickly.

Wow, that sounds like quite a story the mechanic is telling you. I'm not saying that he is wrong, but I would want to know exactly how he came to that conclusion? How did he determine that the oil changing wasn't done? I've really never heard of an oil pump getting clogged with sludge, but I guess its possible. I would think that if the engine was bad from this you could tell from compression testing, or buring oil from excessive wear. Also, how does he know that there is more sludge? Popping the oil pan off should reveal quite a bit. I would seriously consider having another mechanic give an opinion (one that you trust)maybe even a dealer? (without telling them what the current mechanic has diagnosed).

Hope it works out.

db

News to me so the previous owner must have rarely changed oil. Has the oil pan actually been removed or is your mechanic guessing? The sump screen should stop debris before it enters the pump itself. It's unlikely that the pump itself is damaged but something before it might be leaking pressure, like a bad o-ring.

I'd remove the pan if not done before and after cleaning the sump screen, replace the oil pan and sump o-rings. The pump is in the very front of the engine, behind the front crank seal, not inside the oil pan area. Then check oil pressure with new oil. It'd have to be very bad to continually clog the sump screen, like ALOT of loose sludge which would be very rare.

While the pan is off, it'd be a good idea to check rod and main bearings as if worn, that'll also cause low oil pressure.

As for the dealers responsibilty, you'ld need to prove that they knew it had engine problems before you bought it. If they knew this, was it disclosed to you on a safety sheet?

If it wasn't disclosed and had no obvious noises, oil light or problems indicating a worn engine when you bought it, you'ld have a hard time proving fault on their behalf. It's then "buyer beware" as things like that can and do happen with used cars, sometimes you get a bad used car.

Does your mechanic have EXPERIENCE with that Volvo engine, not just older 4 cyl "red" engines or otherwise? If not, I would highly advise getting another opinion from someone experienced with the newer Volvo "white" engines.

$2,500 for a used 850 engine installed would be very cheap as it'll take about 20 hours of labor to swap it, not an easy job. There's also no or little guaranty with a used engine, again "buyer beware".