Was getting some bad temp spikes on cold starts due to the classic 22RE thermostat design issue. Looking at the OEM dual stage thermostats and they are pretty steep in price at around $40+.

I found two aftermarket dual stage thermostats that run at 192deg F. I picked one up at autozone because they had it in stock nearby. Both go by part #41492 and appear to be manufactured by Motorad with Duralast and Murray branding. I've been running the Duralast ($9) with a FEL-PRO Thermostat Gasket #35278 in my 1993 22RE and the temp spikes have gone away completely on cold starts. Temp also seems to be more stable overall as well. Time will tell if the reliability is any good, but my last cheapo bargain thermostat lasted over 200,000 miles.

I also wonder if the dual stage thermostats are inherently more resistant to catastrophic failure of failing shut compared to single valve designs? If one of the valves fails shut, it's maybe far less likely that the other will fail shut at the same time? Might get a few more miles before the temp gets too high to drive even if just running on the smaller valve.

 

Another decent little mod to do while you are there is to drill a small hole in the thermostat flange. I did that clocked opposite of the little jiggle valve that is there already. I am not seeing any temperature spikes and the system burps itself after a coolant change without any special coddling.

 

Thermostats are, theoretically, designed to fail open. Supposedly, when the wax puck finally goes away, the valve is supposed to open and lock there. I know, they've been known to fail both ways. I'm just saying that's what's SUPPOSED to happen.

Notice the words theoretically, supposedly, and so on
Pat☺

 

I think what happens most with failed thermostats is that the valve sticks when it is fully expanded with heat and stays open. When the valve wax melts or leaks out of the piston it no longer can push against the spring which holds the valve closed. The second case is more rare, but has happened to me before. Clipping the spring allows the thermostat to stay open for emergency use until it can be changed out. The thermostat on the 22RE has to be the easiest thermostat in history to pull, even on a hot engine. I just put a rag over the housing (catch spray), use a long socket extension, and crack the bolts to release pressure, then change it out. I had a string of bad luck overheating thermostats over 20 years ago in my 93 truck due to another cause overheating the engine and melting out my thermostats. Takes about 5 minutes.

 

Ive done this too, works great. Or just pull the jiggle valve right out.

 

I bought one from LC Engineering listed as Toyota T-stat but has TAMA WW52EM-88A package inside (here). Buying direct or from other sellers maybe less expensive.

 

Alright, I am confused.

What actually causes "temperature gauge overshoot"?

After looking at the cooling system, the coolant for the heater circuit starts at the intake manifold, goes around the engine to the heater valve, through the heater core, and through a pipe that ends at the water pump, right?

This means that the "cool" coolant from the heater core isn't being dumped right in front of the thermostat as everyone says, but is returning to the same place where the "cool" coolant from the radiator re-enters the engine.

Is this right, or do I have this backwards?

 

NAPA stocks the Tama brand thermostats. They sell them under the Altrom line. Bought one for 92 pickup 22RE about five years ago, and it does just fine.

https://www.napaonline.com/en/p/ATM1...put=thermostat

 

Wish I could say. All I know is that adjusting the blower temp in the cabin has an effect on the engine temp. Set it to cold and the engine runs colder. Set it to hot and the engine runs hotter. Mine has always done this to a degree, as far as I can remember. I think the temp spike only happens on cold starts since the thermostat is totally shut and the warmed coolant has a hard time getting to it before the engine gets hotter than it should.

 

I'm sure the temp spikes seen when using a single valve thermostat don't really hurt much, especially since it only seems to happen on cold starts. My truck has over 320,000 miles on it NOT using dual stage thermostats and runs better now than it did 150,000 miles ago. LOL For a couple of buck extra though, might as well use something better suited for optimal functionality.

 

From what I've seen, the "cool" from the heater core comes back into the main system just before the thermostat. When the Throttle body is off you can see the small pipe where the heater water comes back into the main system. Holds the thermostat closed longer than if the heater return was after the thermostat. That's why the gauge goes high on these trucks. Until the engine temp plus the heater temp add up high enough to pop the thermostat, the gauge, which only reads the engine temp way before the thermostat, goes high. Once the thermostat opens, the waters mix, and the gauge is now reading the two together.

All this is to say just why they came up with the two-stage thermostat. It lets SOME engine and heater water through, so the engine doesn't go as high, before the main valve of the thermostat pops open.

I've also seen, on mine at least, that the main valve doesn't just go all the way open and stay there. At first it will open all the way, but that will get the water too cool, so it closes SOME. Then that's not enough, so it opens more, gets too cool, closes some, etc, etc, until it settles on the correct amount of open to keep the water at the temp the thermostat is designed for. You can watch this happen on the gauge. I use a single-stage thermostat in mine. It goes high, as expected, then drops way down when the thermostat opens. Then it comes back up somewhat, almost 1/2, then down, but less than before, and so on, until it settles on the temp it wants.

Just my experiences...
Pat☺

 

The odd thing about the temperature overshoot during warm up was the inconsistency. Not every Truck or Celica exhibited the condition, so thermostat replacement was on a 'need-to" basis. Toyota was/is remarkably consistent in their manufacturing, and typically if you saw something on one vehicle you would see it on many. But not the overshoot. It truly seemed rather random.

 

I have the OEM thermostat on my '87 22RE and I've *never* seen any temperature overshoot...except when the water pump belt broke. And the truck has lived in Midwest winters.

 

Makes me wonder if some have some sort of restriction that has developed, and the dual-stage is just buying some time. The rather few vehicles we saw with overshoot bitd were fairly new at the time, less than 2-3 years in age. And after a few years of keeping 1-2 in stock we phased them out completely as demand dropped.