496mag / 496HO - How many hours is too many hours?

[Bigbore500r]

I know as well as anyone that this is a loaded question - but what kind of life are people typically getting out of 496Mag / 496 HO motors?

These aren't getting any younger, and a lot of the used boat market consists of 500hr boats from the 2000's, some of them that are pretty sweet and in great shape but getting up there with the hours.

Assuming it's not a "key on" error or an insane amount of idle time, what kind of hours are people getting out them before they need a tear down?

 

[ONE-A-DAY]

ive seen 496's in the 1000 hour realm, its not so much the hours, rather what was done as far as maintenance goes along the way. 500 hours on a 20 year old boat is only 25 hours a year.

 

[GRADS]

I've seen them go well over 1000 hours without even a hiccup.

 

[ONE-A-DAY]

It also depends on where you buy the boat from, west coast boats are used year around, not the case in the east or midwest.

 

[mjc]

I blew a head gasket at 475. I could have probably just put in gaskets but I got carried away. I honed block, replaced all bearings, rings and did valve job because it was out of the boat. Runs great now.

 

[JB in so cal]

I've got about 480 on my '05 and it's been trouble free aside from a faulty drive fluid bottle sensor. Services every year. Love it. But these days it's 2 adults and 2 dogs in a magic so it's a spring chicken lol

 

[Bpracing1127]

I have a friend with 1200 and never opened up. Top speed on his boat is the same since day one

 

[TrojanDan]

We have close to 700 hrs in our '02 Magic Wizard with a 496HO. Bought it 6 months old with about 60 hrs. Starts every time and runs like a champ. Now it's the backup boat to my pontoon.

 

[Rbcconst]

My neighbor has the HO and has 1100 hours.

My boat has 500.

I would and did do 2 things before buying a boat with 500 hours

#1 do the compression test or dont buy it.

#2 get the hours scanned and get the breakdown of how many hours at what rpm. 2/3 of the hours on my boat were under 3000 rpm. It virtually has no hard hours on it.


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[H2O]

Even if the compression checks out and the boat was very well maintained, there is a minor hidden problem to be aware of on that generation of Merc motor.

The paint inside the Cool Fuel Module can come off and clog up filters, fuel rails and injectors. (lots of photos of this online, especially OSO) When I was shopping for used 496HO boat, I just assumed that if the cool fuel module hadn't already been replaced I would be doing along that, with the complete fuel system and injector cleaning. A well known shop owner in TX told me lots of undiagnosed problems and early failures could be traced back to contaminated fuel system from that Module. (Injector cleaning is probably not a bad idea at those hours in any case, all it takes is one injector running lean...)

Not saying it happens to all motors by any means, just something to consider when shopping.

I believe the attached Mercury service Bulletin was issued for this reason.

 

[Shlbyntro]

With regular maintenance and use, hours are fairly irrelevant. They are great engines once you get past their Achilles heal which is the fuel system. These engines are extremely susceptible to fuel system failures, normally due to lack of use. Almost all the engines I've seen with holes in the side of them have been 496s. The common denominator in every failure was that they were not run regularly and an injector failure either flooded a cylinder or leaned out a cylinder and the engine grenaded shortly there after.

If you're buying one, have an inspection done by a mechanic who knows how to read spark plugs. If you end up buying one, have the injectors taken off and sonic cleaned and flow tested from the get go.

Some serial ranges on this engine (Mercruiser) are eligible for free fuel pump and fuel injector replacements from Mercruiser. They will provide the parts but the boat owner is responsible for labor. Must be performed by an authorized Merc dealer.

This was out of a 496

 

[02HoWaRd26]

With regular maintenance and use, hours are fairly irrelevant. They are great engines once you get past their Achilles heal which is the fuel system. These engines are extremely susceptible to fuel system failures, normally due to lack of use. Almost all the engines I've seen with holes in the side of them have been 496s. The common denominator in every failure was that they were not run regularly and an injector failure either flooded a cylinder or leaned out a cylinder and the engine grenaded shortly there after.

If you're buying one, have an inspection done by a mechanic who knows how to read spark plugs. If you end up buying one, have the injectors taken off and sonic cleaned and flow tested from the get go.

Some serial ranges on this engine (Mercruiser) are eligible for free fuel pump and fuel injector replacements from Mercruiser. They will provide the parts but the boat owner is responsible for labor. Must be performed by an authorized Merc dealer.

This was out of a 496 View attachment 840144

What’s the advantage of sonic cleaning and flow tested as well who can do that?

 

[Shlbyntro]

Sonic cleaning the injectors will remove and film deposites left behind by old fuel and any debris that may have made it up to the injectors from other parts of the fuel system like the fuel pump. I personally always make a point to flush the fuel rails and lines too while I have it apart. Flow testing them afterwards just insures that you got everything out and that they are working properly. I want to see less than 10% variance between injectors.

Many shops these days have bought the machines to do this as it is becoming increasingly important with the ethanol fuels. Any reputable shop should be able to do it for you or at least have a specialist that they will send the injectors out to. As a customer, request a detailed flow report.

 

[Ricks raft]

Really depends on how it was driven. I think a scan of hours would be an indicator.
I can't believe how many times when at the launch ramp I see someone fire up the boat and as soon as they reach the 5 mph buoy hammer down, often less than a minute. My boat will idle in gear until up to operating temperature and then gently apply throttle till on plane so gear oil has a chance to warm up.

I bet in the last 100 hrs it has less than 10 minutes at wot. Always full synthetic lubes.

Agree with fuel problems when I bought my current boat I didn't do a leak down test and it had old fuel had a slight hesitation, within minutes lost 2 cylinders complete rebuild. so my fair deal purchase became a poor deal. But now I know the motor and should be good for a thousand hours.

 

[Tank]

What are you looking at now Jerry?! Like others said, hours are semi irrelevant from what I've seen. They routinely get 1,000 + hours out of them. Though I think if you're looking at something with a thousand hours or close just assume you'll rebuild upon delivery. It seems that I've seen more problems with them after they've sat to long with out enough use. Buddy has a 30ish lavy with a single 496HO he built the boat new it's about 15 years old. Has 130 original hours on it! Took it out last year and it started running crappy. Took it to Barrett, problem with one of the cylinders / rings. We just purchased that Cig that has twin 496 HO's w/300 hrs. Ran it all summer take it in for service, two cylinders are at 75 and 80% compression. So replacing the block while we're going balls deep on everything else. It also sat for last 6+ years. Whatever you look at, get it leak it down and do a compression check on the motors. That will give you HUGE insight into their well being as you know, no matter what the hours are.