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.

I've owned 3x 3rd Gens and in each one, I've found that properly burping the system, having a working thermostat, having a working (new) radiator cap, using the right coolant/ratio and clearing the radiator of obstructions is more important than the position of the jiggle valve.

Others will swear by it, though and my anecdotes are by no means the definitive answer (I put every one at 12 o'clock FWIW), it's just what I found in my experiences.

I think I have an older post on this board (or another) from where I mistakenly attributed a temp drop on my scangauge to reclocking my thermostat, but during that bit of maintenance I also took the [leaking] rear heater core out of the loop and changed the green coolant to Toyota red.

Very good question and worthy post. Personally being an old school seat of the pants kind of guy I tend to go with what I know. And I know two things.
1. Toyota says down.
2. I've always put it UP, because that is how I was taught by Walter P. Chrysler in 1917. His goons the Dodge Bros agreed, but they may have been sucking up.

I am planning a timing belt job at the end of summer and I'll have to decide. Personally I don't believe the whole 15 degrees of swing fantasy. Come to think of it I don't believe any fantasies, although I do enjoy some of my own. I especially like the one where my 3.4 gets better gas mileage than my 3RZ. But I digress.

It makes so much more sense to me to have the valve at 12:00 because the air bubbles tend tow move upwards. But that isn't a scientific explanation, just sort of eye balled. I'd be willing to consider a valid explanation to follow the manual. Hey, maybe it was a misprint? Or the guy was pissed off at his boss and figured he'd live on in infamy by throwing us 3rd gen guys a curve. I'm sure he knew we'd be doing timing belts forever.

Hopefully someone truly "knows" the verifiable answer.

I'm curious too. It makes sense that putting it at 12 o clock would work best, but I saw first hand that relocating it to 6 o clock yielded a 10C temperature drop. That was with a system that I thought was properly purged, so it seems that 6 o clock is indeed the correct position as per the FSM. Having the position correct might also be important at reducing cavitation on the water pump.

Note that you won't be able to tell the difference by using the gauge cluster temperature indicator, but you will with an OBD reader.

Well I will play the game too.

My guess is that hotter water tends to go up in a system. When the valve is at the 12 OC position, the small stream of hot water going through the giggle tends to follow the upper part of the hose, not hitting the functional part of the thermostat, where it will make the spring open up.

At 6 OC, the hot stream of water hits directly the functional part of the thermostat (which is in the middle of the thermostat), heating the wax faster and opening the thermo at a lower temperature.

Here is my guess

Yeah, it defies logic but it sure makes an 8-10 degree difference.

I think it's probably just a result of the flow characteristics of that section of the cooling system.

I helped a friend do the water pump on a Tahoe with the 5.3L V8 in it over the weekend, and the jiggle valve in that gets clocked to about the 10 'o clock position. There's a little nub on the gasket to make sure it goes where it's supposed to, so there was obviously some effort made to make sure it goes in that specific location.

This seems like a reasonable theory to why the jiggle valve needs to be in a certain position.

You may be onto something. I don't know much about fluid dynamics but perhaps we are mistakenly assuming that since air rises, the jiggle valve must be at the top where the air is supposed to be. Maybe we should consider that the coolant may be aerated while in motion or that if there is air in there, the air is not actually at the top. Who knows how the coolant and air behave in that particular section. Restrictions, expansions, obstructions or other "things" might play hell on the flow characteristics of the coolant.

Yep.

The consensus from various threads I've read on this subject is that the way the coolant flows through that portion of the system simply makes 6 o'clock the correct position for the valve.

I think there is definitley something to it. Before I flipped mine I would see temps as high as 209*. Now this was with a radiator with 175k miles and older coolant, but with the new radiator, coolant, and thermostat flipped to the correct position per the TSRM I have yet to see temps over 193* and that's with 100* ambient temperatures sitting in stop and go traffic with the AC on.

When i do my thermostat i want to try the 6:30 position.
A new radiator is a good part of better temps

No, No! You got it all wrong. Who puts a thermostat at 6:30? It's got to be 6:25.

Guys... You're thinking too much about it. It's like Electricity. It's nothing more then MAGIC!

I had high temps the whole time I owned mine, which I found out when I bought my Scan Gauge. Changed everything in the system except the radiator and still no change. This was before knowing about the Jiggle Valve. So I found FOR ME, I have to have an OEM T-stat and in the 6 O'clock position and my temps dropped up to almost 20* in some conditions.

If you use Amzoil coolant, then the position of the jiggle valve makes no difference!