I'm looking at a boat that's a 2001' w/twin 5.7 volvos. It has 675 hours on the original engines and drives used in saltwater with raw water intake. The boat has no bottom paint and is realtively clean so I'm guessing it was rack/lift stored. They had to replace the risers. Are these engines trouble? I'm going to have a survey done before I buy. but what is the expected longivity of a saltwater used engine?

675 is a lot of hours on any motor. As to the salt question some folks flush the engines out after every use ( I would recommend strongly) but my bigger concern would to do a leak down and compression test.

Yea, I figure they will need to be rebuilt soon. I was wondering if the salt corrodes the block, manifold and heads to the point where there will be weakness and cracking.

Flush it after every run and you wont have a problem. I leave it running for 10 minutes. That would be more than sufficient.

If they only had to replace only the risers the engines probably have full closed cooling. That means they run regular antifreeze in the engines and exhaust manifolds. If that is the case, your engines will be in fine shape regardless of salt usage. The sbc is a stout engine and I would not recommend a full rebuild at 675 hrs unless there is something amiss such as oil pressure low. I would recommend a valve job and new springs at 500hrs, which would make you due now.

Dont know about those motors but I have 496 s closed
cooling that has 640 hrs and not a problem with any-
thing. Dont know if that has oil coolers if it does
change them at 700 to 800 hrs and keep on boating !
I ve seen 496 s in fla. that have over 3000 hrs and
just regular maintence.

I agree, I got 3000hrs out of a 5.0L (in fresh water tho) without ever getting into it. Lots of maintenance over the years that's all.

Yes, salt water causes corrosion inside the intake, block and heads. Probably won't crack, but they will eventually just corrode through.

With proper flushing, they will last much, much longer.