4.5L 250 Mercruiser break in

[Shamanlk13]

I just bought a 2018 Monterey that has a 4.5L 250hp mercruiser. According to the manual during the first 10 hrs I'm not supposed to run less than 1500 rpms for any real period of time. I was wondering how critical this is, because at our lake there is some tricky sandbars you have to cross and I generally like to run real slow over them? Anybody have any thoughts?

Thanks

 

[tpenfield]

My thought is that the time it takes to traverse the sand bars would not amount to 'any real period of time', unless the Merc manual is more specific about the timing.

Let us know how you like the new Mercruiser, as those are the new breed of 'purpose-built' engines, vs. the GM re-purposed engines that have been used by Merc (and VP) in the past.

 

[Shamanlk13]

Thanks. So good so far. Haven't "opened it up" but did go about 3/4 throttle and seemed to respond really well.

 

[Cortes100]

That breakin process (1500 rpm) from the manual is sort of strange, but I tried to follow it as much as possible. I would start engine and try to limit idle time. Normally I start the engine and let it warm up while getting stuff ready to go. In this case, I'd raise the rpm to 1500 as soon as possible and get out of the launch area or the shallows. Once warmed up, then get up on plane. As per the manual, I tired to follow it. No WOT launches (slamming the throttle down), lot of variations on rpm when cruising, and no WOT across the lake. I now have about 30 hours on it. It has excellent power band, very quiet and it's good on fuel. Also love that adaptive cruise control, comes in real handy. So far so good with mine.

 

[Bondo]

According to the manual during the first 10 hrs I'm not supposed to run less than 1500 rpms for any real period of time.

Ayuh,..... Welcome Aboard,..... The jest of that is, ya shouldn't go out, 'n troll at idle for the 1st 10 hours,......

Normal launch, putter out, get on it abit, short cruises at the mid, 'n upper power band,..... Whatever,.....

Go enjoy yer boat, idlin' through sandbars ain't gonna hurt athing, so long as ya don't ground the drive,.....

Good to hear good news 'bout this motor,..... I still ain't laid eyes on one yet,......

 

[Scott Danforth]

the higher RPM is to get some load on the motor to get the rings to seat.

 

[Shamanlk13]

Thanks for the replies. Its killing me not being able to let it rip!

 

[Cortes100]

In this case, I'd raise the rpm to 1500 as soon as possible and get out of the launch area or the shallows. .

The above don't sound right........(won't let me edit).
I wouldn't raise the idle to 1500 rpm in neutral. There's no way to not idle the engine, I just tried to limit that.. I would get it into gear as soon as possible, and run at 1500 rpm till warmed up.

Not sure what Merc's theory is behind that. Over the years, I've broken in many new engines and there are many different opinions on how. But since they are the builders, figured I follow their method. One thing I did find out, the shop did a scan on the computer and it shows the engine running history.