coolant leak on radiator return (?)

hi guys, picked up a 2001 tundra a few months ago and have been doing the maintenance myself, this truck was bubbad to all shit when i got it. having a hard time trying to find the fix for this part. it pisses coolant from here when under pressure. would this be sealed with black RTV or is it a gasket? dealership couldn’t help because i’ve got a mismatch of 2001/2004/2002 parts for the whole car

 

The thermoastat has a grooved o-ring that fits over the circumference. Be sure the mating surfaces are clean and not pitted. Be sure to install thermostat with with jiggle valve at 12 oclock position. If still leaking might have to replace thermostat housing cover or thermostat housing. Can you be specific as to what parts are what year on your FrankenTundra?
https://youtu.be/O87xkB0mavQ?si=at2NCiJCmKVqfSeF

 

A ton of info/links to common coolant leak issues are in this thread, search for "Coolant" and you'll find the bullet with all that info.

But it looks like you've either got a crack in the neck, or a gasket leaking out, or lack of a gasket.

That thread I linked also points you to a sticky thread to dig into exploded parts diagrams, so you can see how things go together, and what you may be missing.

You should probably hit that 1st link I sent, read thru it. It'll help you on your journey, probably a lot. Great starting place for common issues, TSBs etc.

 

And using that 2nd link with a random V8 2001 access cab truck, I came up with this: https://toyota-usa.epc-data.com/tun...03/?frame_no=5TBBT48131S134593&full&picture=2

There is a t-stat gasket 16346-50010

But beyond that, looking at the FSM (there's a link to it in my 1st link above), see the pics after this exploded, there's no call for FIPG between the water inlet and inlet housing. It only calls for FIPG between the water pump and inlet housing. That gasket appears to be the only seal, and is identified as non-reusable, maybe someone reused previously? The "New O-RING" they point out in the FSM screencap, last pic, it's another common leak source, that ring wears out.

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thank you all for the advice!! after a little more looking it appears to be the gasket but i will replace the thermostat with it. thank you very much for the part location guide ive got about 300$ worth of shit for different cars at this point trying to fix it up. i believe the gasket was reused as well as the radiator and its hoses were replaced a few years back by the same person who taped up cracks in the air box to get it running lol

 

Ouch.

Just know, a proper t-stat for these trucks should have a jiggle valve or hole-punch looking thing at one point. That needs to be clocked at ~noon on the dial, anywhere between 11 & 1 will work, to ensure air bubbles can get through. Don't want to overheat due to air bubble getting trapped. It's the one thing I'm not seeing mentioned in the FSM in the pages I captured for you above.