It is amazing how many boats with 500EFIs are for sale with 300 or more hours on them most don't want to deal with them and I don't blame them. IMO Mercury did a pi$$ poor job on reserching thier gasket choice. Just my observation

some would say but i still love them over the 502 efi's. we all know that in this hobby you gota pay to play.

very true statement "you gota pay to play" no argument there....

I pulled mine down with 340hrs on it...head gaskets were still good, valve springs averaged 410lbs and lifters were good. But replacing everything anyways for piece of mind.

at 345 i had one motor that the gaskets where burnt out and had hot spots on the other motor... just do them u know they wont last a nother 350 hours like the new springs u will be putting in.

Yea, maybe Iwas lucky since my motor has had a fairly easy life. Doing everything while its apart.

Some last suggestions before you spring to play with the big boys ......In order of importance ------->
1. The engines and drives are the most important parts of the boat --- So...do not trust any one's word about anything !!!
2. Take oil samples of both engines and send them off to Blackstone Labs in Fort Wayne ,In.
3. Do not trust hour meters -they Lie,Lie,Lie----have some one with the right tools hook up with the ECU and check the hours that way - only way to tell who is telling the truth...
4. You know how the commercial asks to see the paper work---- in this case if the guy claims to have rebuilt anything in the engine compartment ask to see the receipts...No one is going to throw out those if he spent thousands of dollars to have a job done.
5.350hrs should be the red line for those engines
If the guy really wants to sell the boat he will comply with your requests ---- If not walk away.


Good luck

Jim