You had mentioned @fj40z that sometimes the tailpipe smelled sweet, sometimes not, back on page one. Besides the weird oval, how did the HG look after teardown? Were any pistons shiny/cleaner than the others? Hear me out, but I wonder (as mentioned above) that you could have missed final torque on a head bolt, so when it's cold a bit of coolant weeps by and is burned off out the tailpipe. Engine gets warm and it seals up good enough to stay together. That sweet smell from the tailpipe is a telltale sign that you have some coolant leaking, which would also be apparent via a clean piston. Take that theory, and add to it you're getting some juice in the oil, and I'd start to think maybe the headbolts weren't torqued just right. Was your Hg a Toyota part I presume? Did you use anything on it, such as gaskacinch or other products? I've seen that stuff work wonders on 22R/RE engines, and become a nightmare on a SBF. It's also been near two days, what's the update also?
