When is a Mercruiser engine to be replaced?

Z

zeehond_nl

Member
Sep 22, 2010
102
The Netherlands
Boat Info
2004
Engines
Mercruiser 5.0 MPI with Bravo III drive
Hello there . A question from a newbee.

You see a lot off boats with several engine hours. I'am searching for a SR 270 in the years 1998-2001. I see different hours. From 200 to 600 hours.

When is an engine to old and should be replaced? In other words...must a make my search blind for a low as possible hours with the engine?

Because when I see the price of a new 454 block.....that almost the half of the boat price!


Thanks for the reply.

Greetings from the (cold) Netherlands,
Marco
 
Marco, the lifespan of an engine has nothing to do with how many hours have been logged.

Thus, low hours also mean nothing. They could be replacements for abused engines, or they could be neglected, never used, never maintained...
 
Warm wishes!

There isn't a simple answer. I personally would prefer a well maintained 1000 hour 454 over a poorly maintained 200 hour version. The general rule I have heard is a lifecycle of 1500 hours on a gas engine and 2500/3000 on a diesel, but I think that there are too many variables to make those numbers meaningful. Keep in mind that 100 hours a year is a LOT of boating for a recreational boat. That means that even on your 600 hour version, you could have nine years of ridiculous boat usage before the engines approach the end of their life cycle.

Good luck with your search. It sounds like any of the engines you have looked at are within their useful lives.
 
GENERALLY speaking.....very general. I have been told that a merc. with RAW water cooling is on borrowed time after 15 years. This is a GENERALITLY. Maintenence is key here. If the engine is FRESH water cooled, the longevity is longer. So a fresh-water cooled engine would be a better choice over a raw-water engine with less hours/years. Make sense?
 
Katricol,
You talking saltwater?
 
Maintenance is key. I have about 900 on my '81 Merc 260 Alpha and it starts first time, every time. No knocks, ticks, spits, sputters, misses, nothin'. It just sits there and purrs. Compression is actually within 2% on each cylinder and it uses no oil. I had an old Starcraft Islander that wasn't maintained, and that 165 Merc sounded like somone was inside it trying to hammer their way out. Just an old fishin boat, so I didn't really care. But if you maintain 'em, they'll love ya for it!!
 
Definately, maintenance maintenance maintenance!. I forgot to mention that I still have the 327F outta my old Chriscraft Cruiser. That was a '67. I fire it up on the stand every other year or so. You wanna hear a sweet engine, this is it! Hmmmm. I wonder what it'd do in my Sea Ray... Hmmmmm.
 
We have 1750 Hours on two 454. Change oil every 100 hours. They use 1/2 quart of oil during that time. Just changed plugs, rotor and rotor cap after having the boat 1100 hours. Thing one side had had a been done the other I do not think so, Boat always started well and still does. I have been told to expect 3500 hours minimumon 454. We run engines between 1200 and 1800 RPM some times go to 3600.
Does anyone have any idea how long the spark plug wires last and where is the best place to get them.
 
northern said:
We have 1750 Hours on two 454. Change oil every 100 hours. They use 1/2 quart of oil during that time. Just changed plugs, rotor and rotor cap after having the boat 1100 hours. Thing one side had had a been done the other I do not think so, Boat always started well and still does. I have been told to expect 3500 hours minimumon 454. We run engines between 1200 and 1800 RPM some times go to 3600.
Does anyone have any idea how long the spark plug wires last and where is the best place to get them.
Click to expand...

When I had 454s I replaced spark plug wires every 3-4 years. That boat seemed to be hard on plugs and wires. Current 8.1s are still running the same wires and plugs (Platinum) and I plan to have look at them at the end of next season and possibly replace them even though the plugs still look good at this point.
 
sbw1 said:
When I had 454s I replaced spark plug wires every 3-4 years. That boat seemed to be hard on plugs and wires.
Click to expand...

I've kept about the same schedule, but I'm not even sure why - they look good and perform well at that age. It's just one of those easy maintenance items.

Re: age, My 454's have just under 1,200 hours and are still going strong.

If someone were to offer to swap me a pair of engines with 200 hours but no maintanence records, I'd refuse.
 
A good friend of mine has a 33 Amberjack with 454's and 3700 hours on them. He recently had a compression check done and it showed strong all the way across the board.

Heres his maintenance schedule:

-Oil change every 100 or so hours in the engine and trans.
-Plugs every year
-Wires every 3
-Cap and rotor once so far
-Run it

This particular boat is fished and run pretty hard, shows it doesn't take much to keep them going.
 
I recently did a search on this and came across a study. It said boat gas engines last 1200 hrs on average. Mine quit at 1190 hrs so they were right. Talking raw water cooled. Probably a lot of 5.7 as they are common. Mine was an 1989 5.7 Mercruiser. Generally, they die from cast iron corrosion. Cast iron turns to scale and comes off in layers. Pull the hose to the exhaust manifold and if you see black sand like metal, that is what is happening. The water passages get clogged up. I was astonished how how some of the passages were totally blocked in the heads. The intake manifold was so thin at one spot, a screwdriver went through with a tap. Compression, power and oil consumption were all good right up until water was found in the cylinders.
 
Is there a study to show how soon a fresh water cooling system will pay for itself?

I can't imagine justifying cooling engines with saltwater.
 
My 5.7s have 1469 hrs each they are within .5 miles of each other and run like new.I put 67 hrs on them this season and when draining the blocks they were a little dirty.I think a lot of it was from going past the coal piles when leaving and entering the river channel.I used about 1/2 quart of oil between the two all season.I am thinking at 1800-2000 hrs updateing to mpi's at 5 grand each or less if i can find some low hr s on a wreck first.
 
Cruisers also build up more hours than go-fast boats in general. A 70mph go-fast at 200 hrs has more wear than a cruiser at 700hrs.....unless the cruising is done at WOT. I run at 3700rpms about 50% of the time.....the rest is at 1500rpms. My go-fast constantly runs at 3,000-4000rpms while boating......no 1500rpm cruising at all. The 454 in the 270 has 750hrs and uses no oil and runs very smooth but loves gas compaired to the 350 in the Carlson CV-23. Corrosion or freezing of the block, heads and risers/manifolds usually kill a boat motor, Mike.
 
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andyr said:
I recently did a search on this and came across a study. It said boat gas engines last 1200 hrs on average. Mine quit at 1190 hrs so they were right. Talking raw water cooled. Probably a lot of 5.7 as they are common. Mine was an 1989 5.7 Mercruiser. Generally, they die from cast iron corrosion. Cast iron turns to scale and comes off in layers. Pull the hose to the exhaust manifold and if you see black sand like metal, that is what is happening. The water passages get clogged up. I was astonished how how some of the passages were totally blocked in the heads. The intake manifold was so thin at one spot, a screwdriver went through with a tap. Compression, power and oil consumption were all good right up until water was found in the cylinders.
Click to expand...

The other engine just went! 21 years old and they fail within days of each other! I would have expected 5%-10% variance which would be 120 hrs difference. So, both failed at 1200 hrs. Just cast iron rust/scale lets water into the cylinders.
 
JediJD said:
The general rule I have heard is a lifecycle of 1500 hours on a gas engine and 2500/3000 on a diesel, but I think that there are too many variables to make those numbers meaningful.
Click to expand...

Interesting comment on diesels. My mechanic and I were just talking about the life of the Cat 3406's in my boat and he said those engines in a truck will run about 10,000 hours (close to a million miles) before they need major work. The boat had 850 hours on it when i bought it and I'll never get close to 10,000 hours.
 
andyr said:
The other engine just went! 21 years old and they fail within days of each other! I would have expected 5%-10% variance which would be 120 hrs difference. So, both failed at 1200 hrs. Just cast iron rust/scale lets water into the cylinders.
Click to expand...

Wow... I just replaced my port 454 in a 1990 310EC -- riser failed and sucked water..... Put in a long block with new carb, starter, water pumps, intake, alt, etc.... basically only kept the valve covers, spark arrestor, pulleys, and oil pan from the old one.

I also replaced the STBD manifolds and risers and that motor seems good... good compression, power, no oil burn, etc.....

Hope mine doesn't go the same as yours... both motors were original, salt water cooled, and kept in the water year-round in So. FL. I did put in a fresh water flush kit and flush now after every use.... Not sure what help that will be for the old engine though it surely can't hurt... LOL!
 
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