853468 Mercruiser NUT, (M8)

Illustration 1 g00921815
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.
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 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
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 Gp 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 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.
Illustration 3 g00286269
8T-2700 Blowby/Air Flow Indicator
The 8T-2700 Blowby/Air Flow Indicator is used to check the flow of air through the radiator core. Refer to Special Instruction, SEHS8712, "Using the 8T-2700 Blowby/Air Flow Indicator" for the test procedure for checking blowby.
Illustration 4 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.
Illustration 5 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.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 antifreezes and coolants that contain ethylene or propylene glycol. Checking 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.