I was told by the salesman that sold me my Fountain that the 525s needed new valvesprings and a valve job at 250 hours. I also read of many header failures around that time. I bumped into a "fellow Fountain owner" at the boat ramp and he had just repladed his headers (expensive) and had to go through the engine (to the tune of 7k) due to the water damage from the leaking headers (slightly over 250 hours on the boat - a 2004). We share the same mechanic and the mechanic said the new CMI headers seemed to be much better quality than the OEM headers. He also was very impressed with the 525 engine itself. My question, experienced owners or mechanics only please, is what have your experiences / expenses been? My wife and I are thinking of moving up to a 38 or 42 Fountain and the 525 engines seem to be what most of them have. We would be using the boat 80% of the time in salt water and flushing with saltaway.

With 525s and CMIs. 200-250 is the magic number for checking into them before something goes real bad. It also depends on how hard you run them and maintain them. Best bet is to put $50 per hour in a rebuild fund

Correct. I have done many 500 HP, 500 EFI, and 525 EFIs and by 300 hours almost every one had broken springs.

I had a customer call saying he was going to do the Lake Cumberland poker run and then drop it off for upper service. Just under 350 hours.

He didnt make it, dropped a valve and destroyed the engine.

OEM headers are CMI, and are very prone to leaking also yes correct.

There is no one simple answer. If most hours are hard running near WOT then rebuild top ends sooner, such as by 250 hrs like many of the threads on here say. If the hours are high middle to medium rpm hours, with very few hrs over 4800 rpm, you have longer. Two years ago I asked everybody I could find about this question since I have 525s with over 250 hrs about 320 now. I called dealerships and asked questions on multiple forums. Most of the answers were "rebuild top ends at 250 hrs or less, and bottom ends every other top end rebuild". However interestingly when 525s are put into lower performance boats like cruisers or are used less aggressively the hours on virgin motors can get considerably higher. One fresh water dealer told me he had a larger Formula cruiser trade with 800 virgin hours on 525s. I got numerous answers of virgin motors in the 400 hours range on Cigarettes and Fountains not driven aggressively. Other factors include oil change interval, whether you buy the BS that 40 or 50W single grade is the way to go or if you follow the OEM recommendation of multigrade 25W-40 or 15W-50 which greatly improves top end lubrication on start up and reduces wear over the long term. Other factors shortening life and leading to earlier rebuilds were salt water use and failure to adequately flush after use in salt water.

This is my recent shopping experience:

Lots of 525 boats out there and SURPRISE they are for sale in the ~250 hours range. They are usually priced as if they didn't have a top end job in the future too.

If you're certain you need a 525 boat, you'll love it I'm sure, but go in to the market assuming you buy it and take it to your shop immediately to do the top ends / baseline all maintenance. After that, you'll have lots of fun boating ahead of you. As said before, probably not smart to gamble waiting.

I wussed out and bought a 496 35' boat.

Ditto exactly...but I ended up with a 496 32 footer

The 525 is a great motor. Merc didn't use the best valve springs. Many I have read have found broken springs by 300 hours. Headers should be checked at least annually no matter what engine they are on. I would personally pull heads every 300 on any good performance motor and keep em fresh. Big block bottom ends are beastly of you avoid catastrophic failure.

Merc Race power is all about the maintenance, just like any other built performance engine. Finding a seller that has all receipts, maintenance and top ends done when needed is a rarity on the used market.

I've owned two 525 powered boats. There are two issues: Headers and valve train. The headers you need to pressure check often. I have a system setup to be able to check them with air pressure and a leakdown tester while they're still on the boat. I typically check them every 10-15 hours. Check them regularly and you can save yourself a tremendous amount of grief and $$$. Second issue: valve train. There are many cases of these engines going for 400+ hours without any issues, but there also many that have blown up around 200-250. The safe bet is to replace springs and rockers at 200-250 hours.

I asked my dealer about used 38' Lightenings with 496 power and he said there were not many make as it would be underpowered. I realize "underpowered" is an opinion but I would think a 38' with twin 496s (425h.p.) would be a 75+ m.p.h. ride. And no header or early topped service would be needed.