Hi from newb! I've believed that the 500efi engines were very reliable! I am now strongly considering a pair with 400 hrs. Without being a fortune teller, hoping, those who have experienced these motors over the years, might have insight, as to what to expect for upcoming expense, how about reliability, and longevity! Thanks for any helpful suggestions!

With 400 hrs, they are at least due for top end rebuilds and possibly even full rebuilds.

I have seen a set with 750 hours still sealed, ran in a 40SS Formula. When I got my set they had about 350 hours and they were leaking at the exhaust valves some so I redid the heads. Both of them also had some pinholes in the headers, which seem to be the weak link. The bottom end has some real nice parts in there, should be good for 800-1000 hours easy. I suspect many have failed from the headers leaking, otherwise, great motors.

My 12 year old boat, 380 hours, fresh water only. Leakdown this winter avg = 17-20%. Motors have not been run hard and other then changing oil, spark plugs, plug wires, caps and rotors, one alternator, raw water pump impellors, circulating pumps because of seal leaks, so, i'm tickled with my 500 efi's. These motors still pull easily to 5200 rpm and no header leaks. Oh, and i added msd boxes when new to clean up rich idle condition (causing soot on transom).

Can you give more detail on that mod?

I would love to clean up the soot

Werent most of the issues fixed in the later models (01-newer) fixed?

I owned the boat for a couple of months, no help from mercury, nasty soot on the transom. Added msd 6 (blue boxes), bosch platinum plugs, gapped @ .045 and eliminated about 80% of the soot.