Time for an update on this! Let us 525 owners learn from each other. We've all heard the recommendations for top end rebuild at 200-250 hrs. I want to know how many VIRGIN hours you got before your factory engine failed or you rebuilt "to be safe". If no repairs yet post your hours. If engine failed include what happened. Include your oil type if you want. Happy reading!

I have a 42 Fountain with 355 hrs no problems whatsoever. Only use Mercruiser semi-syn 25W-40.

I don't have anything to contribute except this is a great idea to gather some real world data.

A 2007 Model had about 225 hrs and I heard tapping. Took it to Eddie Young and good thing I did. Eddie found that Needle bearings from one of the rockers had let go, but we caught it before it destroyed the lower half. BTW, Eddy's the man for 525 rebuilds if you didn't already know that.

Previous boat 05 353 Fastech 525s / ITS. Top ends done at 320 hrs, engines were sealed never worked on when we bought with 280 hrs. No failures, just sensors going bad. Teardown revealed head gaskets were starting to seep into each other and valve springs were very weak but not broken. Rockers and headers were all ok. Rebuilt heads, replaced lifters and pushrods for durability.

400 hours on my 525s in a Formula 400SS took the heads off just in case, all good except that valve springs were way weak so probably would not have made 450 before one broke

450 hours on 05 525s. Most 4K to 4500rpm. Oil changes and filters.

Thanks everybody!

630 hours on my 500efi's unopened

Just had motors opened up at 340 hrs. Both stock. 1 motor was still tagged, sealed. The other had been opened at some point. Valve seat pressure was really low around 100 pounds. Valve train was in tack, but showed signs of wear and lash. Full valve train replaced. Head gaskets were starting to seep between cylinder walls. Cylinders still have a cross hatch. Heads are in great shape. Changing out composite head gaskets with multi layer steel. Port matching heads to intake and exhaust. Opening up heads around exhaust valves. Ive ran Amsoil Dominator full syn in it past two seasons. Royal Purple was in them before that. No failures. Zero issues. Run er hard as she'll let me. Top 85.7 MPH at 5400 rpm. I show the .7 because its not 86mph. YET.....

How will you achieve the proper RA for the MLS gaskets on the engine block?