Originally Posted by Xsbank
What is the "air bubble" theory?
I think he's talking about cavitation corrosion and why you should run astm d6210 coolant in wet liner engines. Avoiding silicate additives as well should you have a keel kooler.
Here's some stuff from Bob Senter on the subject.
Diesel Marinization - there's more to it than you'd think!
Let's clear up what "marinization" means. You start out with an Assembled block, cylinder head and fuel system, then
add the peripherals that make it a marine engine. This process often makes or breaks an otherwise perfectly good
diesel. There is a lot more to it than first meets the eye.
1. A larger, preferably heavily cast, oil pan is specified for maximum oil capacity, but it has to be shaped so that it doesn't
make the engine so tall it will be uncompetitive with other engines and difficult to install. It also needs provisions for
different dipstick locations and oil drains compatible with low bilge locations and tight stringers.
2. A different valve cover may be specified for additional oil vapor/mist separation, noise dampening and resistance to
rust and corrosion. Marine engines often require optional oil fill locations and crankcase breather choices.
3. A marine-specific exhaust manifold must be installed - something completely different from any other application. The
Coast Guard requires the manifold to be heat shielded so that if something flammable comes in contact with it, there's
no fire. This can be accomplished with very expensive insulation (space shuttle tile material) and heat shields. That
improves engine efficiency about 10%
compared to a water jacketed manifold because more heat is available to run the turbocharger. Turbochargers and
exhaust elbows must also be insulated or water jacketed. Again, water jacketing reduces efficiency but may present a
slightly cooler surface for decreased radiated heat to the engine room. Higher output engines absolutely REQUIRE
water jacketed exhaust system parts to absorb the thermal stresses - dry insulated manifolds crack under those
conditions. Needless to say, water jacketed parts in expensive diesels are cooled by the engine's antifreeze/coolant
mixture because sea water is too corrosive.
4. A marine specific intake manifold is generally required for packaging efficiency with the cooling and exhaust systems
that are completely different from land bound applications. In order to meet current NOX emission requirements,
turbochargers are almost universally required on any engine over 100 HP. Turbocharging raises the temperature of the
air going into the intake manifold, requiring some sort of cooler to keep it cool enough to allow the engine to meet Nox
emission laws. <<Nox is formed by high combustion chamber temps.>> That "aftercooler" component may be either
seawater cooled or jacket water cooled. If it is seawater cooled, there is a strong possibility that the engine will be
destroyed by a leak into the manifold - depending on how seriously the engine manufacturer considers this issue, it will
directly affect the cost of maintenance and life expectancy of the engine. Engineering this part is one of the most
expensive and critical parts of marinizing. It is VERY expensive and, not surprisingly, where many marine engines are
deficient. A jacket water cooled aftercooler is almost totally reliable, but maximum horsepower available is limited
because it can't cool as much as a seawater aftercooler.
5. A marine-specific cooling package must be engineered and installed. The cooling package must include a heat
exchanger, coolant surge tank, Seawater pump and plumbing, a transmission oil cooler and engine lube oil cooler.
Engines that already incorporate jacket water engine oil coolers are very easy to adapt to keel cooling, although keel
cooled engines require ENORMOUS transmission oil coolers because the return water from the keel cooler is only 15 -
20 degrees cooler than the what came from the engine.
6. Marine grade, moisture resistant starters and alternators are specified. To make the engine's packaging dimensions
more compatible with a boat engine compartment, the locations of the starter and alternator are often re-engineered,
requiring new brackets and different flywheel housings. The entire electrical wiring, circuit protection, harness and
connector system and instrumentation must be re-engineered for marine requirements.
7. Marine engine mounting engineering and mounts must allow maximum flexibility for installing the engine with its
centerline over, under, parallel with or at an angle to the stringers. Then you have to be able to reach the bolts.
8. Additional accessory drive capability must be added to allow for the installation of extra alternators, emergency fire or
bilge pumps, hydraulic pumps, or refrigeration compressors.
9. Belt guards compatible with accessory drives must be installed.
To the degree that a particular marine engine builder addresses these issues, they acquire a better or worse reputation
for their engines. That assumes they started with a good engine to begin with.
The best marine engines utilize heavy-duty industrial base engines, typically used in agriculture and construction
industries. These engines all have replaceable wet liners and very robust construction that allows very long life (typically
40,000+ hours) and economical rebuilds - this is vitally important to commercial customers who will accumulate over
8000 hours per year of running time if their application runs 24/7. <That type of construction is completely unimportant
and needlessly expensive in a pleasure boat application that is lucky to run over 200 hours a year.