i personally never heard of any isolation valves or heater valves on the GX460, my understanding is that these heater cores are always “charged” hot.
Yeah, i checked the belt routing as well..

no vacuum filler tool rental, local shop can do it using their tool for $150 this saturday. Fingers crossed!

 

Nice, let us know! And post some pics of your ride im curious now...

 

dont pay him till U take a long test drive.

 

Amazon has a variety of vacuum refill tool sets starting at $29.

 

Okay im lost

pressure tested cooling system - held pressure good.

then drained and vacuum tested and held vacuum good. Vacuum filled coolant.
Ran the engine at 1.7k constant rpm and it held good temps for like 20 min.

But as soon as tried to go for test drive, temp needle went to 12:30 - 1 o clock position

heater temp still hit and miss. Driver side eventually gets very hot after a long time and overheat session.
passenger side is still mild hot compared to driver side.
and rear is still room temperature air.

no coolant loss, oil looks clear, radiator exhaust gas test is still good.

i feel like the coolant isnt circulating properly, the lower rad hose rarely gets warm.

May be some sort of vacuum leak underload around the Heater T’s?! causing air lock to circulation?

I will drop it off at a local shop with good reviews for their diagnostics. Will report back.

 

The fact that it held 1.7k RPM for 20 mins but failed on the road is a huge hint. Under load, your engine is creating way more heat and vibration than it does in the driveway.Since your rear heat is still room temp even after a vacuum fill, you've likely got a physical blockage (maybe a piece of that broken plastic T-stat?) or a T-fitting that is failing only when the engine torques under load.
If the lower hose is cold while the engine is overheating, the coolant isn't completing the circuit. Dropping it off for a professional diagnosis is a smart move ask them to specifically check the coolant flow rate and use an infrared thermometer on those rear heater lines to see exactly where the heat stops. Keep us posted, this is a weird one!
Dropping it off at a shop is the right move they can use an ultrasonic leak detector to see if it's sucking air in through those T-fittings while the engine is actually under load.

 

Do you have any history on this vehicle such as how often coolant was changed? Was water pump and radiator ever replaced?

Do you look at OBD data stream for temperature read outs?

I know you said the coolant test for exhaust gas was negative, but I have have a gut feeling about the head gaskets.

 

Update, the shop tackled it for 3 days as well and after multiple flush attempts, still overheats on the freeways test drives

they said it passed the block test, so the only thing they can think of is the new fan clutch not locking and unlocking as it should.

I will go pick up the car and replace the fan clutch when it arrives. So tempted to call it a loss and trade it in for a another vehicle at this point

 

I don't buy the fan clutch argument. At freeway speeds, air naturally moving through the radiator should be sufficient.

Did you ever look at OBD data to see what temperatures are being read out?

 

A cold start in the morning would be an easy way to check it with out replacing it. The fluid settles after awhile and it's temporarily locked up.
REALLY obvious at first start as I probley wake a few up in my neighborhood.

I would look at that thermostat again too.

Thanks for keeping us up to date

 

yeah I hear the big fan whooshing sound and it goes away. But i can see why the shop suspects the fan clutch, if it locked once it got hot, it should cool.
But even when on freeway speeds, it wont cool with just passing air, unless the fan is locked and somehow creating an air wall effect behind the radiator, preventing through flow of air.

i took out the newly installed Aisin thermostat and tested it in hot water and it opened as it should. And it cannot be installed backwards in our design…

i was watching the Car Care Nut channel and how he was able to find this super odd issue of aftermarket sensor throwing weak signal causing the computer to throw misfire code.

Could it be possible that my GX had the ECT sensor code in previous life, owner replaced it with aftermarket sensor, throwing weak signal causing overheat senseation and when I rev it out, somehow it gets enough electrical current through and coming right back down to 11:45 position on the temp gauge??
okay im thinking too hard and too much into this…

does OBDII read temp from another source? If same source through a potential faulty sensor, i wonder if it would show overheat through OBDII as well?

 

There is only one engine coolant temperature sensor.

You mentioned you might take the vehicle to another shop. Not sure where you are located, but Ahmed from the Car Car Nut would be all over this. His shop is located in Homer Glen, IL, a Chicago suburb. People drive (and ship) their Toyotas to him when other shops can't fix them.

 

Wiring diagram is needed if its a sensor side issue.

And just to confirm, on idle in park, the car wont overheat with accessories like air conditioner on?

Finally your front grill and fan are obstruction free? Like no winch/offroad bumper/bug screen?

 

theres always Carvana.

 

i really wish I could, but i’m in Honolulu, HI lol
i guess nothing is impossible but still

The car won’t overheat if it’s just idling with AC on. Underload eventually it will fluctuate. Not complete hot but like 12:30 position.

yeah my front grill and bumper are stock.