Is anyone aware of any typical problem areas or weaknesses in the Mercury Racing 500 EFI engines? Also, how many hours are people typically seeing before needing to do overhaul work.

They are good motors. Nothing fancy, decent hardware.

If the motor has been run "fairly hard" then you need to consider lifters, valvesprings, locks, and might as well check the roller tips on the rockers - at 200-250 hrs.

The bottom end of the motor shouldn't need any special care until past 600 hrs.

Aside from the above, they are known to be pretty reliable and tough.

MC

Thanks, I'm doing some boat shopping and that's just the kind of information I was needing.

Rod

The earlier serial numbered 500EFIs have only one fuel pump on them which can lead to some vapor lock issues in the extreme heat of summer (as me how I know). Later serial numbers actually added a second pump to the raw water pump to cure that issue.

Other than the one time I had a vapor lock issue, the engine has been very reliable, very fun and fast. Its nice to just turn the key and not have to worry about it.

Great engines, of course I may be biased since I have two. Only problem was a fuel pump relay that went bad this year, simple to replace. I also replaced the valve springs and CMI exhaust headers proactively this year, 250 hours, 12 yrs.

On boats with LWP bravo and XR drives, there were some issues with head gaskets getting tired and leaking, due to excessive water pressure. Not too long after the 500 EFI and LWP drives came out, Merc Racing made a pressure relief valve kit that you could install to prevent the excessive pressure. Later Bravo 1 and XR drives with DWP's reduced the pressure alot, in most cases. If you search on 500 EFI head gasket failures, you should find it. Otherwise great, bulletproof engines. Not a lot of computer sensors to fail and keep you guessing "which one is it this time", without having Diacom software, and not as frequent header failures with the E-top headers.

great engines,,headers are known to leak tho...figure 7-8 k their for a twin engine boat..

awsome motors! iput over 750 hrs on a fresh water set.very reliable,

You did 750 hours without a top-end overhaul?

Header issue is only 525EFI