Cooling Systems For Marine Engines
If you cruising around in your boat, you are riding in one big huge radiator
. Unlike your vehicles water supply, I doubt
youll ever ride long enough to heat up the entire lake to the point your marine engine will run hot. For most marine
engines, raw water is drawn into the lower part of your out drive through small holes by a water pump. Some boats have water
pumps housed in the lower sections of the out drive unit, and some have raw water pumps mounted on the engine, and they are
driven by a belt, or shaft. Those mounted on the engine should not be confused with the circulator pump on the front of the
engine, such as the one you have on your car or truck! As you will read later, it has a different job to do.
Removing the oil cooler inside of the fan housing raised the temperature at the 3/4 head as much as 50 degrees F above
normal. That's right, it went up by 50 degrees, not down like the people selling outside coolers would like you to believe.
In fact, upon looking at some of the ads for outside coolers they stated that the 3/4 head changed by 50 degrees, and never
stated that it would cool better than stock. Air flow was drastically reduced at the head and increased at the lower part of
the 3/4 cylinders.
These raw water pumps pull water from the lake, and push the water towards the engine. Most raw water pumps are made with
metal or plastic housings, and use rubber impellers to pump. Although many get years of service from the small rubber
impellers, I think it is best that they are changed each year when normal service is performed. Often, when they do fail,
they send debris and rubber pieces throughout the cooling system resulting in blockage. At that point, the system must be
back flushed and cleaned.
We even discovered that the thermostat shutters are directional devices to direct air to the proper locations through warm up
and also when they are opened all the way to direct air to the most critical areas.
Speaking of thermostats, removing the shutters and the thermostat increases engine wear 15% to 17% and often causes cracked
heads even in southern California. Naturally, the percentage is much higher in colder areas. The internal engine parts cannot
heat up and expand together at the proper rate when the thermostat is removed.
First, lets talk about why water goes to the exhaust system first, if not the same time as the circulating pump, or engine
block. Water MUST get to the exhaust manifolds rather quickly so that they do not overheat. They must have a steady diet of
cool raw water flowing through them all the time so that they stay nice and cool, even while the engine is getting up to
operating temp. If not, the exhaust system would seriously overheat, and burn any rubber connection hoses associated with
it. In extreme cases, it can catch the bilge of the vessel on fire. Your exhaust manifolds should never be excessively hot
to the touch. I am not in anyway telling you to go out and touch them after running the boat either.
The more we tested, the more apparent it became that the heads are the source of the heat. We found the CR and volumetric
efficiency of the engine is a large factor. When heads, CR, carburetion, exhaust and cam are all correctly matched to the
engine so the volume of fuel (proper octane) and air is what the engine wants, the engine runs cooler and lasts longer. For
long life, we recommend conservative compression ratios, especially because pump gasoline quality has been going down, down,
down from the good old days.
It is very important to keep your cooling system in proper operation. The system often gets debris in it, such as sand,
trash, grass and parts of broken impeller lodged about. I know of several on this forum that have had cooling system
problems on both inboard and inboard/outboard engines. Sometimes it takes a while, but the systems can be cleaned and
repaired.
by: karan123
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