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Mysterious coolant leak? on 2004 tundra 4.7 v8

I’ve been having this issue for about a week now, and I’m starting to get stumped
Hoping anyone here has any insight on direction I should take, any help is appreciated.

So about a week ago I was driving and I noticed my temperature gauge spiking up to full and almost instantly dropping back down to normal, did that a couple times inconsistently before I was able to pull over and check things out, noticed my coolant was low topped it off with water, everything went back to normal and I assumed it was a leak.
After looking all over for a leak I couldn’t find anything externally. I checked my oil cap and noticed white milky sludge in the cap, instantly thought it was a head gasket so I got a block test to check for combustion gases in the radiator it passed that test. I looked further down the oil fill and noticed the oil in the engine is clean and so was the oil on the dipstick, assumed it was just from short drives in a humid area (pacific north west). So I took it into a shop and had them do a pressure test and lift it up to see if they could find any external leaks. They said it held pressure and couldn’t find any leaks externally and that it must have just been an air bubble or a bad radiator cap so I replaced the cap, topped off the coolant and a few days later I was low again. I decided to get some UV dye to put in the coolant and my own pressure test kit, when when I did the pressure test I pumped it to 16 psi and over the course of 10 minutes it dropped to 14. No visible leaks anywhere.
My next order of business is to pull all the plugs, pressurize it and check the cylinders for coolant.
Other notes: white smoke/steam from tail pipe is only during startup and once it gets to operating temp, goes away.

My questions for you guys is

-what are all the ways coolant can enter combustion chamber ?

-if coolant is getting into the combustion chamber will there always be sign of exhaust gases in radiator?

-how long should radiator pressure test hold pressure and at what psi?

-if it was a head gasket or something with the block would it be driving/idling/and operating normally for the last week?

-anything else you think I should check before I start taking things apart ?
 

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Speaking from experience don't throw money buying parts and guessing. How old is your radiator? Where the top and bottom caps are attached they start to leak over time but you should see a few drops or a little weeping. The transmission cooler is integral to the radiator and they can rupture internally but your transmission fluid would be milkshake. How is your fan/clutch. When cold give it a spin. It won't cause it to loose fluid but can cause temperature spikes. Outside of water pump and thermostat you might check lines and the cab heater core but you would probably smell and see water. Smoke at start might indicate the beginning of a head gasket issue but if you tested the block??
 
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