That's a lot of coolant to supposedly be making it's way into the exhaust stream without any evidence of burning. Did you check above that area for leaking hoses, fittings, etc? You're talking about missing tubes, and while I don't know enough about these vehicles yet (just bought my '19 HiHy last weekend), it doesn't seem plausible that what you're seeing is entering the exhaust stream without massive amounts of white smoke being present at the tailpipe.

 

The coolant in your highlander should be red.

 

THAT!

 

That plug definitely has an issue, but it could be that it isn't firing consistently as it looks like the gap is wide than the others.
There isn't anything else that would be green except coolant. How it is getting onto that exhaust is the question that needs an answer. Obviously, it is doing that when cold as it would burn off instantly when driving. It seems too far back to be from the water pump. Maybe a heater line or the heater core. Good luck finding it.

 

XLRtech is right, the coolant is red, as while I was watching an oil leak at the front right while running, a pink drip appeared on the lower water pump bolt... I guess I get to do all the repairs and maintenance the car should have had 50k ago now...
The green/yellow liquid is a mystery for sure. The condensation dripping from the tail pipe is clear.
As for the plugs, yes, they were all about .050 from wear. Just did a 9 mile, "around the block" drive and it runs smoother and the throttle response is better.

 

If you have coolant coming from the weep hole unfortunately you are going to need to replace the water pump. Had to have my 2017 done at 43k two months before the warranty expired. How does the brake fluid look it can turn a greenish when its old most people don’t replace it when they should.

 

it could be AC refrigerant. It might also be that the trans fluid was replaced by a non standard green fluid.

 

This seems to come up a lot when it snows, but could just be condensation reacting with the metal in the exhaust and perhaps leftover road salts.

https://www.toyotanation.com/threads/quick-fluid-question-neon-yellow-green-under-car-in-snow.281370/

Also:
"After a few quick science lessons curtesy of google, I finally had my answer. Turns out the mystery fluid was a result of the recent snow storm we had. The state of New York isn’t very shy about their use of road salt. They must use mountains worth every winter. To fully understand the cause you have to know what kind of metal used in modern exhaust systems. The main culprit being zinc. Used to help prevent rust in galvanized metals, actually turns yellow when combined with iron and a catalyst. As it turns out salt makes a great catalyst for corrosion."

Random Google search results:

https://www.fox21online.com/2019/12/03/mechanic-explains-what-that-yellow-snow-under-your-car-is/

Neon Lime Green/yellow Fluid Leak - Solved

I have just spent the afternoon troubleshooting a potential fluid leak from my Toyota Rav4.2 and I've just found the solution. The cause of the apparent fluid leak was so unlikely, I decided to post it here in case it saves somebody else the same stress!The situation began with the recent snowy w...

www.toyotaownersclub.com

 

A/C refrigerant boils and evaporates at room temperature, no way it's getting to the exhaust as a liquid and there is no path for it to cross over. A/C is is a completely separate and sealed system from the engine. In 53 years of working on cars, I've never seen green trans fluid, but I suppose it exits somewhere... so no, I just did the pan drop and filter change with 4 quarts of fresh. Oil was dark red, but, thankfully, only smelled old, not burned. I do hear ya on the trans fluid getting in the engine. The old GM automatics had vacuum modulators that, when the diaphragm ruptured, would allow the vacuum to pull trans fluid into the engine, but never at a rate high enough to run out raw. Plenty of white smoke when it got bad enough ...LOL
Tech,
Yes, I will be looking to replace the WP in the near future. I need this buggy to be trustworthy and reliable by January for a road trip to Tucson. I haven't looked at the brake fluid, other than to verify the reservoir has enough for now. Doubt it has been "exchanged", nothing else has, so far.
Question that just vibrated the cob webs...is the gasket between the Y pipe and converter Copper ??? I know that metal will turn green from age and corrosion. WAG that maybe the greenish liquid is coming from something like that ?

 

Thanks for the link. At least I know this isn't an isolated issue. The reaction of the raw, toxic, exhaust fumes with stainless, before reaching the converter makes some sense. No idea if, or how, that happens, but I'm going to go with that and ignore it. Like I posted previously, the condensation out the tail pipe is clear, as it should be and is most likely the result of having passed thru the converter. I think the other thread supposing it's a winter thing, is because they see it clearly in the snow. Most people don't leave their car running for 10 minutes in a garage for this to show up on the floor.
Thanks folks