Replacing Thermal Air Valve

[hkeiner]

I want to replace the Thermal Air Valve on my motor. This valve closes (shuts off) some of the air flowing to the idle circuit when the motor is cold (resulting in a richer fuel/air mixture) and then opens when the motor warms up. The valve is screwed into the starboard cylinder head and an air hose runs from the valve to the idle circuits on the carbs.​

I figure that this is an easy replacement job but want to be sure about the use of dielectric grease during installation of the valve. The Mercury shop manual does not have any detail instructions on the removal/installation of this valve although the parts diagram does seem to indicate that (#6) dielectric grease should be applied to the valve before installation. This seems to be an unusual use for dielectric grease. I have always used it previously only for protecting electrical connections.​

In an attempt to become more knowledgeable about outboard motor maintenance and repair matters , I have the following questions:​

1) If the purpose of the dielectric grease is to keep the valve from getting seized over time, why wouldn't anti-seize compund be used?​

2) If the purpose of the dielectric grease is to improve thermal transfer from the cylinder head to the valve, why wouldn't thermal grease be used?​

3) Should the dielectric grease be applied evenly over the entire thread of the valve or only at the top edge of the threads (where the treads are near the exterior edge of the cylider head).​

4) What amount of torque should be used to tighten the valve. If there is no specific torque value known (i.e., Newton Meter), should it be "tight" or "really tight"?​

Thanks in advance for any information/tips on this.​

 

[hkeiner]

Re: Replacing Thermal Air Valve

For anyone interested, I went ahead and asked this question at my local Mercury repair shop. The Mercury authorized mechanic said that the dielectric grease is just to keep the valve threads from seizing onto the cylinder head, rather than to improve thermal transfer at the threads or to protect an electrical connection (as there is none). He couldn't explain why dielectric grease is recommended by Mercury over anti-seize compound. I went ahead and applied dielectric grease on the threads, just so that I didn't vary from Mercury's specs, and the new valve seems to be working OK.

 

[WillyBWright]

Re: Replacing Thermal Air Valve

Mercury probably specifies Dielectric Grease because they sell it and don't sell heat sink compound or never-seeze.

 

[allen russell]

it works just like your temperature just screws in the head blank hole! the only difference is the temperature switch is held in with a clamp! my boat has 2 temperature switches one for the gauge and one for the warning buzzer! but the terminal switch works the same closed when cold opens when it gets hot! none of them ever touch water like a car engine!