Rick's Free Auto Repair Advice

What a Thermostat Jiggle Pin Does

What the thermostat jiggle pin does and why it’s important to replace with the same kind

A jiggle pin works when the engine is off to prevent air pockets from surrounding the themostat’s wax pellet. When y ou shut off the engine and there’s no longer any water pressure pushing against the thermostat, the weighted pin falls, providing a pathway for any trapped air to vent through the hole. So thermostat jiggle pin is a bleeder valve of sorts.
image of thermostat jiggle pin

The thermostat jiggle pin acts like a bleeder valve to prevent trapped air from insulating the wax pellet

How does air get into the cooling system?

Any time you flush or drain your coolant you can get air in the system. You can also get air in the coolant if your water pump is creating cavitation, or you have a cooling system leak
When installed vertically, the pin can be located in any orientation.  However, when the thermostat is installed in a horizontal position, the it should always be turned so it’s in the 12:00 o’clock position.

If the the pin is located in any other position in a horizontal installation, the air around the thermostat’s wax element could act like an insulator, preventing the thermostat from opening at the right time. That could cause your engine to overheat.

For more information on how a thermostat works, see this post. For more cooling system service posts, click here

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