This type of system prevents cavitation in the water pump. Cavitation is the forming of low pressure bubbles in liquids that are caused by mechanical forces. It is more difficult to create an air pocket or a steam pocket with this type of cooling system.
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| Illustration 1 | g00286266 |
Boiling point of water | |
Remember that temperature and pressure work together. When a diagnosis is made of a cooling system problem, temperature and pressure must be checked. Cooling system pressure will have an effect on the cooling system temperature. For an example, refer to Illustration 1. This will show the effect of pressure on the boiling point (steam) of water. This will also show the effect of height above sea level.
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Personal injury can result from hot coolant, steam and alkali. At operating temperature, engine coolant is hot and under pressure. The radiator and all lines to heaters or the engine contain hot coolant or steam. Any contact can cause severe burns. Remove filler cap slowly to relieve pressure only when engine is stopped and radiator cap is cool enough to touch with your bare hand. Cooling System Conditioner contains alkali. Avoid contact with skin and eyes. |
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The coolant level must be to the correct level in order to check the coolant system. The engine must be cold and the engine must not be running.
After the engine is cool, loosen the pressure cap in order to relieve the pressure out of the cooling system. Then remove the pressure cap.
The level of the coolant should not be more than 13 mm (0.5 inch) from the bottom of the filler pipe. If the cooling system is equipped with a sight glass, the coolant should be to the proper level in the sight glass.
Test Tools For Cooling System
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 4C-6500 | Digital Thermometer | 1 |
| 9S-8140 | Pressurizing Pump | 1 |
| 9U-7400 | Multitach Tool Group | 1 |
| 1U-7297 or 1U-7298 |
Coolant/Battery Tester | 1 |
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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts. |
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| Illustration 2 | g00313246 |
4C-6500 Digital Thermometer | |
The 4C-6500 Digital Thermometer is used in the diagnosis of overheating conditions and in the diagnosis of overcooling conditions. This group can be used to check temperatures in several different parts of the cooling system. Refer to Operating Manual, NEHS0554, " 4C-6500 Digital Thermometer Group" for the testing procedure.
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| Illustration 3 | g00286276 |
9U-7400 Multitach | |
The 9U-7400 Multitach Tool Group is used to check the fan speed. Refer to Operating Manual, NEHS0605, " 9U-7400 Multitach Tool Group " for the testing procedure.
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| Illustration 4 | g00286369 |
9S-8140 Pressurizing Pump | |
The 9S-8140 Pressurizing Pump is used to test the filler caps. This pressurizing pump is also used to pressure test the cooling system for leaks.
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| Illustration 5 | g00439083 |
1U-7297 Coolant/Battery Tester or 1U-7298 Coolant/Battery Tester | |
Check the coolant frequently in cold weather for the proper glycol concentration. Use either the 1U-7297 Coolant/Battery Tester or the 1U-7298 Coolant/Battery Tester in order to ensure adequate freeze protection. The testers are identical except for the temperature scale. The testers give immediate, accurate readings. The testers can be used for coolants that contain ethylene or propylene glycol.
Making the Correct Antifreeze Mixtures
Adding pure antifreeze as a makeup solution for the cooling system top-off is an unacceptable practice. Adding pure antifreeze increases the concentration of antifreeze in the cooling system. This increases the concentration of the dissolved solids and the undissolved chemical inhibitors in the cooling system. Add the coolant/water mixture to the same freeze protection as your cooling system. The following chart assists in determining the concentration of antifreeze to use. Refer to Operation and Maintenance Manual, "General Coolant Information".
| Antifreeze Concentrations | |
| Temperature | Concentration |
| Protection to -15 °C (5 °F) |
30% antifreeze and 70% water |
| Protection to -23 °C (-10 °F) |
40% antifreeze and 60% water |
| Protection to -37 °C (-34 °F) |
50% antifreeze and 50% water |
| Protection to -51 °C (-60 °F) |
60% antifreeze and 40% water |
Checking the Coolant Recovery System
The following information will aid in troubleshooting problems that could be found during a routine check of the cooling system on a marine engine.
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 9S-8140 | Pressurizing Pump | 1 |
The Recovery Bottle is Overflowing
The following items should be checked when a recovery bottle overflows.
- Verify that no air is trapped in the cooling system. Refer to Testing and Adjusting, "Cooling System - Check".
- Verify that the recovery bottle is not overfilled when the engine is cold.
- Verify that the operating temperatures of the engine are correct.
Leaking Coolant is Visible on Top of the Expansion Tank
The following items should be checked if coolant leaks from the top of the expansion tank.
- Verify that the recovery bottle is ventilated to the atmosphere and verify that there is not an obstruction in the vent.
- Remove the pressure cap on the expansion tank and check for foreign material between the top seal of the cap and the top of the filler neck. If foreign material is present, clean the cap and reinstall the cap.
- Check the condition of the filler neck on the expansion tank. If the filler neck is distorted, replace the filler neck. Also, if the neck contains nicks or excess solder, use an abrasive cloth to smooth the neck. Replace the filler neck or replace the expansion tank if the damage is beyond repair.
- Pressure test the top seal on the pressure cap.
- Pressurize the expansion tank with 34.5 kPa (5 psi) air through the recovery bottle by using 9S-8140 Pressurizing Pump. Ensure that the hose between the expansion tank and the recovery bottle is clear. If the hose is not clear, repair the hose before continuing.
- If leaking occurs between the pressure cap and the neck, replace the cap. After replacing the cap, repeat the test.
- If a leak still exists, replace the filler neck or replace the expansion tank, as needed.
Excessive Coolant is Being Passed to the Recovery Bottle
The following procedure can be used to diagnose an excessive amount of coolant flow to the recovery bottle.
Note: It is normal in marine applications for coolant to be transfered from the expansion tank to the recovery bottle during a typical warm-up period.
- Verify that the release for the primary pressure valve for the cap is 89.6 ± 20.7 kPa (13 ± 3 psi) by using 9S-8140 Pressurizing Pump. If the pressure is not within the specifications, replace the cap and retest the system.
- Verify that the expansion tank holds a minimum of 68.9 kPa (10 psi) pressure with the cap installed. If the expansion tank will not hold pressure, repair the tank or replace the tank.
Coolant Does not Siphon Back to the Expansion Tank
The following procedure can be used to diagnose coolant that does not siphon back to the expansion tank after the engine cools down.
- Perform a pressure test on the coolant recovery system at 34.5 kPa (5 psi). Refer to Step 4 of "Leaking Coolant is Visible on Top of the Tank" for the test procedure.
- Pressure should not leak off more than 3.4 kPa (0.5 psi) in five minutes. If the leak is excessive, inspect the following items for leaks:
- Top seal on the cap
- Neck
- Recovery bottle
- Connecting hose for the recovery bottle
Note: A leak in the system can allow air to be sucked into the expansion tank when the engine is cooling down. This will result in coolant left in the recovery bottle.
- Top seal on the cap
Checking the Filler Cap
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 9S-8140 | Pressurizing Pump | 1 |
One cause for a pressure loss in the cooling system can be a damaged seal on the radiator filler cap.
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| Illustration 6 | g00296067 |
Typical schematic of filler cap (1) Sealing surface of both filler cap and radiator | |
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Personal injury can result from hot coolant, steam and alkali. At operating temperature, engine coolant is hot and under pressure. The radiator and all lines to heaters or the engine contain hot coolant or steam. Any contact can cause severe burns. Remove filler cap slowly to relieve pressure only when engine is stopped and radiator cap is cool enough to touch with your bare hand. Cooling System Conditioner contains alkali. Avoid contact with skin and eyes. |
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To check for the amount of pressure that opens the filler cap, use the following procedure:
- After the engine cools, carefully loosen the filler cap. Slowly release the pressure from the cooling system. Then, remove the filler cap.
Carefully inspect the filler cap. Look for any damage to the seals and to the sealing surface. Inspect the following components for any foreign substances:
- Filler cap
- Seal
- Surface for seal
Remove any deposits that are found on these items.
- Filler cap
- Install the filler cap on the 9S-8140 Pressurizing Pump .
- Look at the gauge for the exact pressure that opens the filler cap.
- Compare the gauge's reading with the opening pressure that is listed on the filler cap.
- If the filler cap is damaged, replace the filler cap.
Testing The Heat Exchanger And Cooling System For Leaks
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 9S-8140 | Pressurizing Pump | 1 |
Use the following procedure in order to check the cooling system for leaks:
- After the engine is cool, loosen the filler cap slowly and allow pressure out of the cooling system. Then remove the filler cap from the heat exchanger.
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Personal injury can result from hot coolant, steam and alkali. At operating temperature, engine coolant is hot and under pressure. The radiator and all lines to heaters or the engine contain hot coolant or steam. Any contact can cause severe burns. Remove filler cap slowly to relieve pressure only when engine is stopped and radiator cap is cool enough to touch with your bare hand. Cooling System Conditioner contains alkali. Avoid contact with skin and eyes. |
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- Ensure that the heat exchanger is full of coolant.
- Install the 9S-8140 Pressurizing Pump onto the heat exchanger.
- Take the pressure reading on the gauge to 20 kPa (3 psi) more than the pressure on the filler cap. The pressure on a typical filler cap is 48.3 kPa (7 psi) to 103.42 kPa (15 psi).
- Check the heat exchanger for leakage on the outside.
- Check all connection points for leakage, and check the hoses for leakage.
The cooling system does not have leakage only if the following conditions exist:.
- You do NOT observe any outside leakage.
- The reading remains steady after five minutes.
Note: Check the engine oil for evidence of coolant leakage.
The inside of the engine cooling system has leakage only if the following conditions exist:
- The reading on the gauge goes down.
- You do NOT observe any outside leakage.
- Evidence of coolant on the engine oil gauge.
Make any repairs, as required.
Test For The Water Temperature Gauge
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 4C-6500 or 2F-7112 |
Digital Thermometer or Thermometer |
1 |
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Personal injury can result from escaping fluid under pressure. If a pressure indication is shown on the indicator, push the release valve in order to relieve pressure before removing any hose from the radiator. |
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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts. |
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Check the accuracy of the coolant temperature indicator or coolant temperature sensor if you find either of the following conditions:
- The engine runs at a temperature that is too hot, but a normal temperature is indicated. A loss of coolant is found.
- The engine runs at a normal temperature, but a hot temperature is indicated. No loss of coolant is found.
Coolant temperature can also be read on the display screens of the Electronic Service Tool.
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| Illustration 7 | g00862270 |
Typical example (1) Ports | |
Remove the plug from one of ports (1). Install one of the following thermometers in the open port:
A temperature indicator of known accuracy can also be used to make this check.
Start the engine. Run the engine until the temperature reaches the desired range according to the test thermometer. If necessary, place a cover over part of the radiator in order to cause a restriction of the air flow. The reading on the water temperature indicator should agree with the test thermometer within the tolerance range of the coolant temperature indicator.