525's
 

can any one please explain the problems, people mention pressure testing and or leak down. I am looking at a low hour donzi with 150 hours. Thank You

Here are the most talked about problems with 525's.

1) Leaking headers: There have been a number of instances of leaking headers causing water ingestion, some leading to stuck valves, others to complete catastrophic failure of the engine. There are a number of preventative steps you can take to discover it early and/or minimize the damage if it occurs.

2) Valve train: A number of people have reported rocker and/or valve spring failures around the 200 hour mark. There are also plenty of people who have run their 525's for 400 hours without a single failure. Luck of the draw to some degree. However, there is good evidence from some very reputable guys that have been fixing these engines that the stock springs / rockers should really be upgraded to better parts. I am in agreement with this.

3) Reversion: The 525 has a lot of overlap in the cam which depending on your exhaust configuration can lead to reversion issues if the exhaust water is dumping too close to the header collectors. This I know to be true as I experienced it myself.

Having said all that, do not fear the 525. It is a relatively simple 502ci motor that makes 550 HP (they have been dynoed up to 560HP) and is generally very reliable. You should get a survey done by a certified surveyor including compression and leakdown tests of the engine(s).

Thank You

Leak Down Test:
https://mobiloil.com/en/article/car-...-leakdown-test

And when folks are referring to pressure testing, especially with 525s, they are talking about the headers. The original headers that came from Mercury on 525EFIs are known to crack and leak, which can ruin an engine. It would be helpful to know what year boat you are looking at, salt or fresh, what kind of maintenance routines were done...
...and if the headers have ever been removed, tested, and/or replaced.

2004 fresh water

And another important factor is have the engine scanned - look into history plus look at true engine hours and what rpms all the hours / minutes have been ran at. It will break it down. Look for fault codes.

Next most likely it will have external hydraulic steering and tie bar - unhook rams at the drives and one end of the tie bar and check for gimbal ring wear and hinge pin location for cracks or lose hinge pins. You are looking not to have any side to side and up and down play of the outdrives.

Find a surveyor that has a scan tool and knows how to use it and knows how to use a leakdown tester, Many of them never ever sat in a OEM service training classes nor even own any OEM service manuals. Some are very weak on the mechanical side but can be strong on the structural side of this. You want both for an inspection. Just saying

2004 boat means a 2003 engine. This vintage header may not have the "cool collar" design. You can tell if the header has the cool collar if you see a small 1/4" section of pipe coming out of the flange and then the outer jacket welded to the primary exhaust runner. If all you see is the outer jacket welded to the flange, you do not have the cool collar. These headers were more susceptible to leakage damage than the "cool collared" ones because the outer water jacket goes all the way to the flange, so if you have a crack there, you're getting water in the cylinder. Also, do not let the fact that it was fresh water sway your thinking. Salt water certainly makes matters worse, but its heat cycles and possible overheating that kills 525 headers. Look for any discoloration / blueing of the outer jackets; that will give you an indication if they've ever been overheated. These headers can also be easily pressure tested while still on the motor with compressed air, a leakdown tester and a few fittings although you're better off spending your time on the engine compression and leakdown tests as those will be more informative as to the condition of the motor(s).

Thanks guys, your info is very helpfull.