I have a 91 4runner V6 Auto, on a recent trip I was having a major over cooling issue, the needle was dropping near the C. I have always had this issue in town, but not as severe, just not being able to reach O/D temp. I figured it was a thermostat issue, Im just pulling out my T-Stat right now and find that the one that is in the truck has a jiggle valve, the one the auto parts store gave me does not.

I remember reading somewhere that 90 and 91's are not suppose have the jiggle valve. Is this correct? Could this maybe the root of my problem? or do I need that jiggle valve?

 

Is there a REAL problem with it being to cold?

Or are you just worried for the reason of your mileage, as it dumps in more fuel when the engine is cold?

 

your thermostat may be stuck open not allowing the motor to heat up

 

Well the problem is the trans wont stay in O/D, so the motor screams along at 4000 rpm when it should be around 2700. I put a peice of carboard infront of the rad hoping to correct the problem, but that only worked for a little while and then it fell out.

 

Sounds like your t-stat stays stuck open. I'd try replacing the T-stat with the correct OEM t-stat, and going from there...

 

when I pulled to thermostat housing, it was closed, and when driving around the temp sits right below where it needs to be to shift into o/d. Is it possible for the thermostat to be opening too soon? And does it need that jiggle valve? I figured that it was a Thermostat issue, because driving around town at around 80km/h it will sit just below op temp, but on the trip doing 120km/h it was dropping way down

 

Also could be a faulty temp sensor, I honestly don't know what T-stat came in the 90 and 91's....
check the FSM here... http://www.ncttora.com/fsm/index.html

 

i remember reading a procedure of putting your thermostat in a vat of water, and heating it up on the stove, until it opens, and measuring the temp of the water.

should be in spec, whatever the spec is.

Your truck has a fan clutch, not electric fans right? My subaru (which has electric fans) had an issue with overcooling when the fan relay shorted to always closed, causing the fans to run at full speed no matter what.

 

next time zip tie the cardboard to the car infront of the radiator.....and if it is mechanical you might have a bad fan clutch...

 

If you do this....make sure you suspend the t-stat in the water, you dont want it touching the bottm or sides of the pot, then your test will be off, and will be worthless.

 

The cardboard was a temp fix, I would like to get this permanently fixed.

 

Any cooling system modifications? Running 50/50 coolant? Where are you located (and more importantly, what is the climate like)?

 

https://www.yotatech.com/forums/f116/crazy-temp-problem-very-crazy-109820/

Also search for overdrive, over cooling, etc.

If the thermostat gets "weak", you can have an overcooling problem. If you replace the thermostat but still have the problem, just maybe it can be cured by burping the coolant system. If that doesn't fix it, then most likely you have a blockage somewhere.

I personally still haven't addressed mine, but winter's over and i have lost my sense of urgency.

Good luck!

 

Also, AFAIK, all OEM thermostats have jiggler valves.

Orient the jiggler to 12 oclock.

I believe it's primary purpose is to help prevent air from being trapped in the sytem during re-fill

 

Im living on the west coast of canada, temp is average around 35-40F for you american's in the winter, right now it's around 45F. Stock cooling system I think. My friend who has a 94 truck said i've got a bigger rad? not sure though, running a 50.50 mix

 

i know we have high capacity cooling systems on our delivery trucks for our summers (100F+), but in the winter, they put tarps over 1/2-3/4 of the radiators because they overcool.

 

You can take a pair snips & cut the jiggler off. Won't hurt anything and you won't have "burping" issues. Definitely orient the hole to 12 o'clock position.

 

Well just replaced the thermostat without the jiggler. Still have the same over cooling issue. the temp stays rock solid at just under half way. Any other ideas? Can I get a hotter Tstat?

 

I thought that's where it's supposed to be....just under half way?

 

if it is, it's just shy of where it needs to be to get the trans to shift into O/D.