Howdy Everyone,

Probably not the most exciting thread like somebody showing pics of their sick mods on their 3rd Gen but I'd really like to find an explanation out there of why the jiggle valve positioning can make such a big difference in coolant temps (around 10-15 degrees).

The FSM says the jiggle valve must be pointed downward at the 6 o'clock position. Some people with the Haynes manual for their trucks says it's supposed to be placed at the 12 o'clock position. Some on this forum have recently replaced their thermostats, including myself, and found the jiggle valves in different position. @StreetCreeper found his at the 1-1:30 position. I found mine at the 3 o'clock position. I placed my new one at the 6 o'clock position and nothing changed. My coolant temps were around 190 before and that's where they are now. @DK327 placed his at 12 and found he was running in the 200's for his coolant temp. When he switched it to 6, his coolant temp dropped to the standard 190 range where most of us run at.

I did some more reading on thermostats and the function of the jiggle valve and found an interesting statement from this Australian Radiator company.

Here's the link to the website:
http://www.are.com.au/feat/techt/thermostat.htm

And a quote:
"All High-Flow Thermostats are fitted with a jiggle pin that enables the system
pressure to be stabilised so that the valve opens easier. The jiggle pin also
allows air pockets to move past the Thermostat and the temperature to be
regulated more efficiently. Fitting High-Flow Thermostats will allow your
vehicle cooling system to operate more efficiently."

I already knew the jiggle valve helped remove air pockets so it would prevent an air lock but this new claim that it enables the system pressure to be stabilized so that the valve opens easier is something I didn't know.

But what is still hard to understand is why the position of the jiggle valve makes such a big difference. Is it possible the coolant piping leading to the thermostat doesn't actually fill completely to the top so a jiggle valve placed at the 12 o'clock position isn't going to be as effective? I would think since the system is pressurized the piping would be full. Could it be something with gravity?

Hopefully some of you mechanical engineering types will be able to explain this because I'd really like to understand what is happening that makes such a big difference with the positioning of the jiggle valve.