826365 Mercruiser NUT, (M8)

Visual Inspection Of The Cooling System
Cooling systems that are not regularly inspected are the cause for increased engine temperatures. Make a visual inspection of the cooling system before a test is made with test equipment.
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.
Check the coolant level in the cooling system. Read the two indicators for the coolant level in the top of the radiator.
Look for leaks in the system.
Make sure that air flow through the radiator does not have a restriction. Look for bent core fins between the folded cores of the radiator. Also, look for trash between the folded cores of the radiator.
Inspect the drive belts for the fan.
Check for damage to the fan blades.
Look for air or combustion gas in the cooling system.
Inspect the filler cap, and check the surface that seals the filler cap. This surface must be clean.Testing The Cooling System
Illustration 1 g00286266
Boiling Point Of WaterRemember 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 the 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. Test Tools For Cooling System
Table 1
Tools Needed     Quantity    
4C-6500     Digital Thermometer     1    
8T-2700     Blowby/Air Flow Indicator     1    
9S-8140     Pressurizing Pump     1    
9U-7400
or
1U-6602    
Multitach
or
Tachometer Group     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 g00286267
4C-6500 Digital Thermometer The 4C-6500 Digital Thermometer is used in the diagnosis of overheating problems or in the diagnosis of overcooling problems. This group can be used to check temperatures in several different parts of the cooling system. Refer to the testing procedure in Operating Manual, NEHS0554.
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8T-2700 Blowby/Air Flow Indicator Group Flow Indicator The 8T-2700 Blowby/Air Flow Indicator is used to check the air flow through the radiator core. Refer to the testing procedure in Special Instruction, SEHS8712.
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9U-7400 Multitach The 9U-7400 Multitach is used to check the fan speed. Refer to the testing procedure in Operator Manual, NEHS0605.The 9U-7400 Multitach can measure engine rpm from a magnetic pickup. This magnetic pickup is located in the flywheel housing. The magnetic pickup also uses the ability to measure engine rpm from visual engine parts that are rotating.
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The 1U-6602 Tachometer Group is a hand held phototach for general use. The 1U-6602 Tachometer Group is a phototach, so this tachometer only registers basic input frequency on any visible, rotating part. The basic input frequency equals one revolution per piece of reflective tape. The 1U-6602 Tachometer Group does not replace the 9U-7400 Multitach .Checking the Filler Cap
Illustrati