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:
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
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.