826709 8 Mercruiser NUT, (.250-20)

Illustration 1 g01106438
Effects of pressure on boiling point of a cooling systemTemperature and pressure work together. When a diagnosis is made of a cooling system problem, both 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.
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.
The coolant 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.Slowly 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.Tools for Testing the Cooling System
Table 1
Tools Needed    
Part Number    Part Name    Quantity    
4C-6500     Digital Thermometer     1    
8T-2700     Blowby/Air Flow Indicator     1    
9S-8140     Pressurizing Pump     1    
9U-7400     Multitach Tool Group     1    
245-5829     Coolant/Battery Tester Gp     1    
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.
Illustration 2 g00876179
4C-6500 Digital Thermometer The 4C-6500 Digital Thermometer is used for the diagnosis of overheating conditions and for the diagnosis of overcooling conditions. This group can be used to check temperatures in several different parts of the cooling system. Refer to the tool's Operating Manual for the testing procedures.
Illustration 3 g00286269
8T-2700 Blowby/Air Flow Indicator The 8T-2700 Blowby/Air Flow Indicator is used to check the air flow through the radiator core. Refer to Special Instruction, SEHS8712, "Using the 8T-2700 Blowby/Air Flow Indicator " for the test procedure for checking the blowby of a cooling system's radiator.
Illustration 4 g00286276
9U-7400 Multitach The 9U-7400 Multitach Tool Group is used to check the fan speed for an engine. Refer to the tool's Operating Manual for the testing procedure.
Illustration 5 g00286369
9S-8140 Pressurizing Pump The 9S-8140 Pressurizing Pump is used to pressure test the radiator's filler cap. This pressurizing pump is also used to pressure test the cooling system for leaks.Check the coolant frequently in cold weather for the proper glycol concentration. Use the 245-5829 Coolant/Battery Tester Gp 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 antifreeze/coolants that contain ethylene or propylene glycol. Test and Inspect the Filler Cap
Table 2
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.