Marine Engine Cooling Systems

 
Inboards and Inboard Outboards
 
Please remember that these pictures are basic - each manufacturer has their own system, but with these pictures you should be able to understand how each system works.
 
There are three basic systems used. The full loop system, the half loop system and the raw water system (they may be known by other names e.g. seawater system or closed looped). Each system is used for a specific purpose but it all boils down to money. The more money the better the system.

 
Full Loop Cooling System
The full loop system is the cream of the crop (most expensive) - and will have very little sea water damage over the years of use. This system allows the engine to operate at higher and more efficient temperature.

 

 
 


 
Half Loop Cooling System
The half loop system is the second best but exhaust manifolds and risers are subject to sea water damage. This system lets the engine operate at a higher more efficient temperature as well.

 

 

Raw Water Cooling System
The raw water system is the cheapest and most common system used and subjects the engine and manifolds to sea water damage. Designed for fresh water use. This system operates at a lower operating temperature to reduce calcium and scale build up inside the engine from the minerals  in the water.

 

 

 
In reference to the pictures.
  1. Raw Water Strainer: To keep debris out of the cooling system. Some strainers have drains some don’t. Some strainers are built into the out drive. Some are just a grill mounted in the hull, and some strainers are a complete unit that is mounted in the engine room.
  2. Raw Water Pump: Supplies cool water to the engine and can be part of the outdrive or a separate unit mounted and driven by the engine. Some raw water pumps have drains but most engine mounted pumps don’t. Those that don’t have drains are to be taken apart and inspected when winterizing. Most outdrives will drain themselves but there are some that have to be inspected to winterize.
  3. Cooler: To cool oil - it can be a transmission oil cooler - an engine oil cooler - a power steering oil cooler - a fuel system cooler or a combination of any or all. Some have drains, some don’t. Those coolers that don’t have a drain will need one of the hoses removed to drain the water out.
  4. Heat Exchanger: Takes the engine heat and transfers it to the raw water system. Most will have a drain, some will have a drain for the raw water and a drain for the engine coolant.
  5. Engine: The engine coolant is used to remove the heat produced by the engine. The engine has its own circulation pump to keep the coolant moving through the heads, intake manifold and the block of the engine. On the raw water systems, the engine block has to be drained to winterize.
  6. Exhaust Manifold: These are water cooled to keep the heat down in the engine room. Raw water and half loop systems must be drained to winterize. The riser should drain with the manifold. On full loop system the riser will usually self drain but not always.

 

Winterizing the Three Systems

Full loop system

  • Drain or replace the raw water system with antifreeze. Blue color in the picture represents raw water.
  • Draining the raw water side of the full loop system.
    • Drain the raw water strainer if possible or drain while cleaning.
    • Drain the raw water pump if possible or remove the cover and inspect the impeller.
    • Drain the cooler if possible or remove one hose connected to it.
    • Drain the heat exchanger - some self drain.
    • Drain the riser or check the manual to see if it drains itself.
    • To replace the raw water side of the full loop system with antifreeze, connect a hose to the intake side of the raw water pump, put the other end of the hose into a pail of antifreeze. Start the engine and run until antifreeze come out the exhaust. There is no need to run the engine until warm.

Half Loop System

  • Drain or replace the raw water system with antifreeze. This includes the exhaust manifolds. Blue color in the picture represents raw water.
  • Draining the raw water side of the half loop system.
    • Drain the raw water strainer if possible or drain while cleaning.
    • Drain the raw water pump if possible or remove the cover and inspect the impeller.
    • Drain the cooler if possible or remove one hose connected to it.
    • Drain the heat exchanger.
    • Drain each exhaust manifold. The riser should drain with the exhaust manifold.
  • to replace the raw water side of the half loop system with antifreeze, connect a hose to the intake side of the raw water pump, put the other end of the hose into a pail of antifreeze. Start the engine and run until antifreeze come out the exhaust. There is no need to run the engine until warm. 

Raw Water System

  • Drain or replace the raw water system with antifreeze. This includes the engine block, water pump, coolers and manifolds. Blue color in the picture represents raw water.
  • Draining the raw water system.
    • Just remove all the drain plugs to let the raw water out of each cavity of the engine and manifolds.
    • Drain each drain port on the engine and manifolds.
    • You should have a stiff wire put into the drain port to remove any scale build up that will keep water inside the engine.

 

Replacing a raw water system with antifreeze.

Inboards

Connect a hose to the intake side of the raw water pump, put the other end of the hose into a very large container of antifreeze. Start the engine and run until the engine is up to operating temperature - collect the water and antifreeze that comes out the exhaust to recycle back into the large container of antifreeze. Check antifreeze strength at the exhaust while engine is warming up. Add more antifreeze to top up the protection strength.

Outdrives

  • Method One: Put the outdrive into a very large container of antifreeze. Start the engine and run until the engine is up to operating temperature - the water and antifreeze that comes out the exhaust will recycle back into the large container of antifreeze. Check antifreeze strength at the exhaust while engine is warming up. Add more antifreeze to top up the protection strength.
  • Method Two: Use ear muffs connected to a pail of antifreeze held above the raw water pump. Run engine until at operating temperature and antifreeze comes out the exhaust. Or run engine until warm with ear muffs and a garden hose, then switch to a pail of antifreeze and ear muffs. Run engine until antifreeze runs out of exhaust.
  • Method Three: Open all drains, let the raw water out, close all drains, remove thermostat cover and thermostat, pour antifreeze into the thermostat housing until full, replace thermostat and thermostat cover.
  • Method Four: Install The Winterizer - pump each water cavity dry and fill each water cavity with antifreeze. Can be used on full loop, half loop systems and inboards as well. Reduces the mess in the hull. The Winterizer collects all of the antifreeze in the spring for reuse next year. Without a mess. No running the engine.

 

Draining Hoses

On the larger engine circulating water pumps, there is a hose that needs to be drained. If not drained, it can cause the connection at hose and water pump to split if frozen. Rather then removing the hose to drain it - there is a hose adaptor by The Winterizer that once installed will remove any raw water that is trapped in the hose. See picture. There is hose adaptors of every size so that you can drain any hose that needs to be drained.

 



Thoughts on using antifreeze or just draining the system.

If you just drain the water system of an engine and leave it empty, it leaves the inside surfaces of the engine to oxidize. This will give you more rust build up inside the engine. This means that the drain ports will have to be cleaned when they are used. If you use antifreeze with corrosion and rust inhibitors, that will reduce the rust build up inside the engine.

The reason that most boaters don’t like to use antifreeze is that it is not easy to recover, until now - The Winterizer is the only one that can recover over 99% of the antifreeze very fast and easy.

Scale, sand and rust build up inside the engine.

The inside of the engine cooling system and exhaust manifolds is where the rust comes from and the minerals in the water is where the scale comes from. Over the winter layup the inside of the engine will rust if left empty. Most of the rust will wash out on start up but there will be some rust that will settle inside the engine at the lowest points. (the drain port is one of the lowest points.) When the rust is sitting at the low point it continues to rust and welds itself together. This is why you have to break up the rust at the drain port with a stiff wire to drain the water from the engine block or exhaust manifold. The only protection you can use to reduce rust buildup over the winter is to fill the cooling system with antifreeze. RV antifreeze is not the best rust inhibitor but is better then none. Green antifreeze is the best but is illegal to use.

Scale will develop on the inside of the engine block and exhaust manifolds when the engine is running. Hot spots inside the engine block and manifolds is where the scale will build up the most but the water flow will break pieces of it off and send it out the exhaust. Some scale will fall to the low point of the engine and or manifold and weld to the rust that is there and make a very hard crust at the drain plug. Scale is not a major problem to worry about, because there is very little that you can do anything about it.

Sand is brought into the engine and manifolds when you hit a sand bar or motor up to a  beach. Most sand is flushed out the exhaust but some sand will settle at the low points in the engine and manifolds. This sand will mix with the rust and scale and can cause the reduction in the efficiency of the cooling system.

 

Enviromental News

Each fall, many boat owners and marinas install anti-freeze in marine engines to prevent rust and to ensure that trapped water will not freeze inside the engine. Although RV anti-freeze (propylene glycol) is now widely used in place of green anti-freeze (ethylene glycol), it is still bad for marine life. Unfortunately, in the process of installing or removing anti-freeze there is often spillage and dumping of these  fluids into the sewer system, storm drains, or even directly into our waterways.

With The Winterizer, boat owners and marina operators can safely collect 99 % of the anti-freeze from the boat engine and can re-use that product year after year. In addition, the process of installing or removing the fluid with The Winterizer takes only minutes and eliminates the need to work deep in the engine compartment.
 

 


Environmental impact of propylene glycol 

Propylene glycol is known to exert high levels of biochemical oxygen demand (BOD) during degradation in surface waters. This process can adversely affect aquatic life by consuming oxygen aquatic organisms need to survive. Large quantities of dissolved oxygen (DO) in the water column are consumed when microbial populations decompose propylene glycol.

The oxygen depletion potential of airport deicing operation discharges is many times greater than that of raw sewage. For example, before application, Type I propylene glycol-based deicing fluid is generally diluted to a mixture containing approximately 50% propylene glycol. Pure propylene glycol has a five-day biochemical oxygen demand (BOD5) concentration of approximately 1,000,000 mg/L. A typical diluted propylene-based deicing fluid could therefore have a BOD5 concentration of approximately 500,000 mg/L. In comparison, raw sewage typically has a BOD5 concentration of approximately 200 mg/L. The amount of fluid used to deice a single jet depends on the nature of the precipitation event and the size of the aircraft but can range from a couple hundred to several thousand gallons. Therefore, deicing a single jet can generate a BOD5 load greater than that of one million gallons of raw sewage. A large hub airport often has several hundred flights each day.

 

 

Sufficient dissolved oxygen levels in surface waters are critical for the survival of fish, macro invertebrates, and other aquatic organisms. If oxygen concentrations drop below a minimum level, organisms emigrate, if able and possible, to areas with higher oxygen levels or eventually die. This effect can drastically reduce the amount of useable aquatic habitat. Reductions in dissolved oxygen levels can reduce or eliminate bottom-feeder populations, create conditions that favor a change in a community’s species profile, or alter critical food-web interactions

Borrowed from Answers.com