I hear you all, thank you. But then this comes down to a “he said/she said” situation . . . the best I could produce is an affidavit (if this came before a judge) from the mechanic that the entire sequence of installation was performed properly - I popped the hood when I picked up the vehicle and saw the new coolant fluid and air filter and belts, etc. - the engine company could allege that those were added after the fact . . . ugh
If they did a chemical test method for exhaust gas in coolant, that test is sometimes misleading. There are confirming tests the engine company may want done too. As posted above, their focus on the misc parts in the cooling system is probably to confirm the cooling system is configured and working correctly and isn’t the explanation for the symtom. It sound like the engine company stands by their product. As long as the terms of the warranty have been followed I don’t think you are going to have much trouble getting this corrected. Don’t presume b/c the one test what the problem actually is though, let them go through their follow-ups.
Following up with engine company tomorrow - my mechanic tested all components they requested and they passed - then sent the vehicle to another shop and without sharing any info said, “car had a fire, reman engine installed, cylinder misfiring” - and they found that the vehicle barely passes CO test at idle, rev the engine and it fails - and that one bank of cylinders is at 150, the other bank starts higher and then slowly declines - so, now three indy shops ID gasket issue