Marine V8 Lifespan ?

[FraidNot]

Can anyone advise of the 'typical' life before full overhaul of a 5.0 or 5.7L Mercruiser?
I have heard from one source 1000 hours is about the point where a re-life is needed.
Lots of factors - sure.....

[u4ea32]

I don't think they wear out at some number of hours. For example, mine still showed as new compression, started easily, idled beautifully, ran like they always did at 850 hours when they died a horrible and expensive death due to failure of the exhaust manifolds letting water get into the engines.

The problem with Mercruisers is not wear of the engine block, crank, pistons, rings, or valves. Its failure due to several factors, perhaps the biggest being corrosion.

Having owned three different mercruisers over the past 13 years, and putting 100 to 200 hours per year on the engines, I have found:

1) Exhaust manifolds are a huge pain. The stockers rust. The aftermarket ones are expensive and they rust and crack. The rust and cracks are not visible from the outside: they can look like new, or even be almost new (mine were a year old) and they fail very expensively.

2) Electricals are a huge pain. There are many connections, and none are gas tight, so every single connector corrodes. This causes unpredictable and intermittent glitches. If the engines are EFI, you also get unpredictable performance, as the engine control computer becomes a GIGO machine: garbage in (any of the many sensor readings get noisy or garbled due to lousy connections) and garbage out (any of the many control signals, such as to the fuel pumps, injectors, timing, also get noisy or garbled). At least its fairly inexpensive and easy to replace the entire engine wiring harness every 4 or 5 years: just one or two boat units per engine.

3) Rust of the block, brackets, ancilliary equipment makes maintenance a pain: when a spark plug you can barely reach under the exhaust manifolds freezes to the block and breaks during a change, you are in an expensive world of hurt. The oil pans are made of crappy steel, so they can and do rust leading to perforation.

4) The drive system itself looks nice but has major engineering flaws. They do seem far better than the mass market competition, but (a) the cooling water passages are a byzantine maze, which means they are very prone to getting blocked by debris and corrosion, so most installations soon require a separate cooling water pickup other than through the drive. (b) The coupler is prone to wear if not serviced annually, and servicing requires removing the entire outdrive, re-lubing the spline shaft, and carefully re-installing and re-aligning -- every shop that has done this for me, and all are Mercury Platinum Certified, has screwed up, so I've had 4 coupler failures. (c) The way outdrives are generally installed leaves the plywood of the transom poorly sealed (just by resin) or not at all, which leads to structural failure of the transom. This failure becomes apparent within a decade for sure.

Personally, I think I have now learned that outboards -- real marine engines -- are far better than car engines.

[FraidNot]

hmm - that is very helpful.
Do you think these issues apply to a newish boat (2006) with fresh water cooled systems - say, with 250 hours on the unit ?

[Pete7]

Originally Posted by FraidNot

hmm - that is very helpful.
Do you think these issues apply to a newish boat (2006) with fresh water cooled systems - say, with 250 hours on the unit ?

Afraid so. It's the mix of salt water and exhaust gasses that take out the risers and manifolds, but you should get 5 years. The other problem with the engines is the electronics and damp salty air. We had the volvo 5.7 variant and thankfully sold it just before the world ended in 2007. Wouldn't have sold it now with the price of fuel in Europe.

Pete

[FraidNot]

- volvo better than the mercruiser in this regard do you think?

[Pato]

I have seen many mercs and volvos with 2000-2500 hrs and still going Which is better Merc or Volvo the same they all use the same blocks it's just the accessories that are different and drives so it's down to luck of the draw and maintanece Treat it nice and it should last

[FraidNot]

Afraid so. It's the mix of salt water and exhaust gasses that take out the risers and manifolds, but you should get 5 years.

Hmm - so perhaps budgeting a new set of risers and manifolds if buying a 5 year old petrol mercruiser is sensible...
Anyone care to pluck an installed cost for this?

[Pato]

3 to 5 hours depending on access at whatever your local shops rates are

[u4ea32]

Mercruiser parts seem to be cheaper and more available than Volvo parts.

Several people I know who have had Volvos swear by them: they swear they will never ever again buy anything from Volvo. I've never owned anything Volvo, they look good to me, but the parts issue I have heard from so many people ...

[Dockhead]

Originally Posted by u4ea32

Mercruiser parts seem to be cheaper and more available than Volvo parts.

Several people I know who have had Volvos swear by them: they swear they will never ever again buy anything from Volvo. I've never owned anything Volvo, they look good to me, but the parts issue I have heard from so many people ...

Is the situation with Volvo parts worse than Yanmar??!! I doubt it -- around $1000 for a starter motor (!!!) for my 4JH3 . . .

[u4ea32]

Maybe that's why so many people like the Kubota based engines: just use tractor parts!

[rhr1956]

Just make sure the boat itself is designed to allow decent access to the engine..front, sides and rear. If you do the work yourself or have it done it will be MUCH EASIER / CHEAPER with good access. My last runabout was a 2006 Tahoe Q6. Decent family boat but damn near impossible to do any work on without standing on your head. I had it 4 years and replaced trim/tilt solenoid (year 2), steering cable (year 3), power steering cylinder ram (year 4) starboard exhaust manifold (year 4). The engine itself was flawless. It's just all the stuff screwed to it that breaks. Each item I had to replace could have been accomplished in a few minutes had there been good access. But nooooo.....

[David M]

Is the block salt water or fresh water cooled, or run in both fresh and salt water? If salt water, was the engine flushed after each use? Or does it have a heat exchanger and uses coolant?

Did the previous owner abuse the engine like running it hard before it has warmed up?

Was the owner one of these people who has only two positions on their throttle, 0% and 100%?

Did the previous owner make oil changes at the prescribed intervals?

Any quality engine that has been maintained and not abused will last for more than 1000 hours.

[sdowney717]

Afraid so. It's the mix of salt water and exhaust gasses that take out the risers and manifolds

Yes, true most setup poorly like that.

On my boat the risers and exhaust manifolds are fresh water cooled part of the heat exchanger circuit.
There is a bronze tailpipe nipple and salt water injection welded onto the end of my risers. From the factory the manifolds were fresh water cooled, not the risers. When I got the boat and had to buy 4 new risers at $200 each, that mod was what I did. And it cools the engine just fine IH 392 Palmer marinized engines.

It cost me around $20 in parts to do that and the risers dont rust out anymore. In my situations was easy to do, other riser setups might be impossible to make that change.

I have the riser on the upper left of this screen capture a number 20 000
it has only a single water exit hole, just plug that remove a couple brass plugs and weld on some 1 inch elbows, weld on a 6 inch bronze pipe nipple to end, drill angled hole in pipe nipple and weld in a pipe for the cooling water and you have a riser that will not rust out. these risers bolt onto the exhaust manifold with no physical water passage between them, they attach to a short stubby pipe end.

Any riser can have a bronze pipe nipple attached to the end and converted to fresh water cooling, but its going to be hard if the riser has many water exits arranged in a circular pattern to weld up all of them with braze. Perhaps it could be done using a plate with a large hole and weld that in first.

In 10 years of use since I converted these, they have remained in good shape and the bronze tailpiece is not degraded. And this in salt water.

For the welding, I used a torch and silver brazing which easily joins cast iron to bronze to stainless steels. I may have used normal bronze rods and flux for the large bronze tail piece. need a good torch to put out a lot of heat to get it red hot.