I bought my great aunts one owner 113k EX to use for my commute. My wife drove it during the holidays and commented the heat never seemed to warm up fully.
I noticed the temp gauge seemed to always stay at the 1/4 or below. I drained the system, replaced the thermostat with a Tama 180* OEM unit, filled with Pentosin A3 blue, bleed per owners manual.

It seemed to do fine on a trip around town. But the heat still never got hot, just warm. I drove it the next day on my 114 mile commute, at mile 30 or so, the temp gauge starts creeping and nearly hits red.
I do the usual steps to reduce temps, also pull over to let it cool. I limp home after work and add more coolant, bleed with the valve.

The next commute, all is fine until about mile 30 on the interstate, again... The air is blowing almost cold. My thoughts are trapped air and/or clogged system.
Yesterday I finally tackled it head on, I flushed the system after running a heavy duty flush additive for 30 minutes.

I pulled all hoses, power flushed the radiator with a water hose, back flushed the heater core using 5/8 tubing and adapter on spray gun. I had good flow at all ports, did not notice any large bits or rust, clear water. I tested the Tama thermostat on the stove top, it opened at the right temp, closed when removed from hot water. I also tested the heater valve, I had my wife turn the temp **** from Hot to Cold, I see the actuator arm rotate, I see the coolant/water flow/dribble left in the core from the flush, stop/start as she cycles the ****.

I blew as much water as I could from the system, reassembled. I filled with fresh coolant, followed the add/purge steps as outlined in the owners manual. I let the fan cycle twice, checked levels, heat felt much better.
I did notice a white chalky residue in the thermostat housing that was not there previously, I assume from an air pocket? Picture attached.

I set off on my commute again today, heat felt better, but not as hot as it should be, temp remained a few ticks below middle but again, about mile 30 the temp gauge starts to rise, the heater temp starts to decrease.
It crept to about a 1/4 below redline, I decided to return home. Now I am dumbfounded, as I think I've followed the air purge and fill steps as outlined in the owners manual.

The symptoms do seem to indicate an air pocket. I have ordered the Lisle coolant funnel that's supposed to assist with filling and avoiding air. Any other suggestions? This is driving me insane.....

 

Not getting up to temp would still be the thermostat. Opening too soon, not getting the inital heat spike from the "stat" being held close appropriately by the spring.

 

I tested it in boiling water, seems to function as designed. It opened fully, slowly as water temp increased, and then closed when removed from water.
As noted, I didn't cheap out, went Tama/OEM $25. Never had an issue with Tama before. And it seems to work when tested.

I think it's an air pocket. Weird it always occurs around mile 30/40. 180 is the correct temp for thermostat yes?
Some of the sites have 170* but other show 180* and my research shows 180* for the 2.3 F23A ULEV

Also, air pocket would explain why the heat comes and goes. Even when it crept towards red, the heater output decreased to cool air, as it did before.
I've never had to fight a cooling system like this out of the 30+ cars I have owned.

I've ruled out a clogged system, water ran fine and clear at all ports when I flushed. The only thing I have noticed is some small gelled up coolant blobs and some small flakes that I can crush with my fingers. Not a ton, maybe enough to make a small pile in the middle of my hand. No rust or hard bits have came out of the system.

 

Can you tell if it is holding back the flow , or only opening and closing? As I see it your only winning half the battle boiling it. It has to hold back the urge to open for a certain time. I never boil it as it is a waste of time.

You flushed the coolant. Did you do it right? You replaced the stat , did you do it right? That will be your air pocket , but it will work through. The system pressurizes.

An air pocket would be noticeable in that event , the coolant level would be significantly lower after 30 miles.

I think factory spec is 190's. There is probably a cold spec and a hot spec based on geographical location.

 

 

You know there is water/coolant pushing on that spring with force from the pump, like over a gallon of water weight pushing on it too. We agree on this, yes.

You simulated this on your stove top boiiling water?

Not testing if it opens , test if it holds closed.

It needs to hold closed to build the heat then open.

 

It held closed until the temp rose, I did not have a thermometer to check water temp but can do so.
I will also buy another thermostat from the dealer and a radiator cap.

The original cap blew the spring out of the housing and it was resting in the filler neck. I replaced with a Murray due to time constraint, and O'reilly's was close by. I just read people having issues with Murray products, so I will replace cap with OEM.

I have never had a Tama thermostat which is OEM, fail me, but it's possible. So I will replace. With the above mentioned, I am starting to suspect a cheap faulty radiator cap not letting the system pressurize, and possibly a faulty new thermostat. The radiator cap seems plausible because I have noticed a few times prior some coolant "spray" in the engine bay. No indications a leak from the radiator itself, so maybe the system has not been pressurizing correctly and now it's further compunded with a cheap, faulty radiator cap. I've read about similar issues with a faulty radiator cap being culprit, rectified with an OEM replacement.

 

The cap not holding pressure would make it go the other way. Overheat. A leaking radiator cap will not cause it to stay cold.

You want that thermastat(stay focused) to hold pressure"closed" and build heat.

Thermonmeter? Don't bother.

 

There's an obvious disconnect between us. The car does overheat, it just has not boiled over yet to date.
1. The temp climbs near redline after 30 minutes/miles of driving, my heater starts to then run cool and the overflow level has dropped.
2. Prior to this, the temp rest a few ticks below middle/normal. Which is abnormal, we can agree on this. It should be resting in the middle/normal range.

Also, I changed oil yesterday, no tell tell signs of head gasket leak.

 

I did not see where you said that it was loosing fluid in the resivoir. That the overflow level continued to drop after being refilled.

2, no idea what your saying .But it sound like the temp is not being controlled, as in not reaching temp , that is the thermostat.

Overheating would be, not holding pressure in the system. Every 1# of pressure is +10 degrees boil protection or something.

It is not going to suck air , but push it out.

Repeating less and less fluid in the resiviors would be a leak .

If the core is empty , no water would be exchanging heat energy to blow out the vents.

Chew on that. Try to apply it to what you have going on. You went everywhere.

 

Stock Nippon thermostat fully open at 191 degrees.

 

A milky solution in the cooling system(thermostat housing) would indicate a head gasket leak. It's time for a compression test.

You can also pressurize the cooling system and see if it holds. It could be bleeding into the crank case via the head gasket.

You also need to check that the fans are both coming on when it's trying to overheat. You could have multiple issues going on together.