Update: Elusive coolant leak issue
I think I found it, but it was too late. Since we were not able to find the coolant leak and we have a summer road trip planned which involves towing a trailer, we decided it was time for the Sequoia to go.
We bought the vehicle used about 9 years ago and started to have issues with it from the start. First a radiator leak, then the water pump went out, which caused a crack in the head so we put in a crate engine. This latest issue caused us to lose faith in the vehicle and we didn’t want to be stranded on vacation this summer.
About an hour before heading out to take the Sequoia across the state to trade it in for a new pickup, I opened the hood to add yet more coolant. At this point I’ve added about a half gallon over the space of 2-3 weeks, so we were hoping and praying that we would arrive without issues. I decided to do one more look over the engine. Lo and behold, I spotted a very small pool of coolant and on the top of the engine right next to the water inlet housing assembly.
Since we had only been driving the Sequoia on short trips it wasn’t getting up to temperature often or for very long, the coolant and able to pool up. I noticed a faint amount of pink crustys at the point where the housing goes into the block.
What I think was happening is the leak was only occurring when the engine was cold/cool and the thermostat had not yet opened up. Since the thermostat was not open, pressure on that side of it was enough for coolant to leak out from the o-ring, but once it was hot and the thermostat was open everything flowed smoothly. This made sense to me because it seemed to go through more coolant on the short trips than the long ones.
Further evidence to support my hypothesis, on the trip across the state, we stopped at a rest stop and I check the coolant level in the reservoir. It was above the cold full line and nothing was as coming from the suspected location.
Hopefully my experience helps someone else in the future to find their own elusive coolant leak.