for sure, can't be a head gasket...it has just as much power as when it was new, pulls hard, no coolant loss, no oil loss. Plus you would think that if it was the head gasket then it wouldn't cool down when turning on the heater? no stored codes on either that bluetooth scanner or a plug-in OBD-II scanner...

 

In regards to the head gasket, while I highly doubt that's the issue, it can fail in various ways that will cause different issues.
The head gasket essentially seals three types of passages between the block and head(s)...the oil passages, the coolant passages, and the combustion chamber (ok, so that's not really a passage).
So depending where the gasket fails will dictate the issue. The gasket could fail between a coolant passage and oil passage, which would cause mixing of the two fluids, which would have no bearing on combustion chamber, which would mean the car should have the same power it always did.
It could blow between a coolant passage and combustion chamber, which would cause combustion pressure to weep into the coolant system...which could cause overheating.
Then it could blow between an oil passage and coolant passage...and so on, and so on.

Turning the heater on will bleed off the heat from the coolant thus lowering it's temp...so the cause of the overheat may be moot at that point because the coolant temp is being lowered another way, from blowing heat into the vehicle.

If there are no codes then I would suspect the sensor is working properly...along with all the other observations about the temp gauge reading.
If the sensor goes open circuit, the temp gauge will read Max Cold, if the sensor was shorted, Max Hot...it really won't fail on a sliding scale.

 

So I did the autozone tool loan program, cancelled amazon order.

Pumped to 17 PSI, after 10 minutes it was 16 PSI.

I did it again and after 20 minutes it still held 16 PSI... that's 1 PSI loss after 10/20 minutes, is that an issue?

I also relieved the pressure, then started the engine to see if there was a spike (dynamic test or something like that) and there was zero movement.





If this is normal then I suspect it has to be the radiator? maybe it's corroded inside despite the high flow? that is the last thing that has not been changed, new OEM radiator cap, new oem thermostat, new oem water pump... flushed the radiator, but who knows maybe that is it and it needs to be replaced like the other guy said

edit: left it on for 30 minutes, stayed at 16 PSI

 

I would consider the pressure test good.
The 1 PSI loss could simply be a larger hose, like the radiator hoses, expanding ever so slightly causing the pressure to drop a little...after the 1 PSI drop it stayed constant, which is really what you're looking for.
If it was the head gasket then the pressure would constantly drop until it either hit 0 or balanced with atmospheric pressure...which would be close to zero anyways.

Literally the only thing left is the rad despite it seemingly flushing ok.

 

Guess I'll order a denso off rock auto and figure out how to get it out, if it's still doing it after that I'm going to light it on fire and say it was stolen lol

 

well well... wonder if we found the problem

 

Here are the repair manual radiator removal instructions (see attached).

If the radiator doesn't fix it I will mail you the box of matches lol!

 

I think you found it...I'll cancel the FedEx pickup of the match box lol!

Well the rad was plugged...just not on the inside like i thought, but on the outside.

If all that is between the rad and condenser, what does the front of the condenser look like?

 

U the man bro, condenser has some bugs but nothing like the radiator... I'm happy to report IT'S FIXED!!!!

Water Pump = $88
Thermostat = $40
Radiator Flush = $3.84
Finding out after all that, that it was just an obstructed radiator the whole time? Priceless.

Oh well, that stuff was due anyways and I learned a whole hell of a lot. Thanks for all your help and everyone else too, one IS350 not getting torched tonight.

The only thing I didn't do from those instructions is disconnect the horn, I just disconnected that wire loom thing and leaned it all forward on the bumper. It was a little tough getting the condenser separated from the radiator, a couple quick yanks did it...hung up at the bottom, thought I was gonna have to pull the thick black plastic thing under the front bumper

 

Rad looks like brand new now.

It's crazy the amount of stuff that was caught in there, considering not much was stuck to the condenser.
I wonder if a little four legged friend brought some of that material in.

 

Just for reference, Napa sell a kit call 'Block tester' for testing burning of coolant. The purpose of the test is to detect exhaust gas inside coolant. If the test is positive, meaning the head gasket is screw.
This is coming from a guy who own an MK3 Supra for 20 years and the MK3 Supra is in-famous for BGH.