New radiator was installed yesterday, because of severe leak. Radiator was topped off with coolant. White milky film observed in old radiator: mechanic indicates that this oil that has infiltrated the coolant system and that there is a leak in the engine.
After install, car was driven 4 miles and parked for 3 hours. Took the car out for a drive and pegged (overheat) the temperature gauge at mile 2 and was summarily turned off to prevent damage.
Attempts to refill coolant showed that it was down at least one gallon. Took the vehicle back to the mechanic at Advance Automotive and could not find the leak. Any guidance / tips to track down the leak are appreciated. Seriously considering a borescope because it is hard to see items.
Diagnostic questions are also appreciated: thank you
Update: I am building a tire-valve radiator adaptor per this instruction: the intent is to pressurize the fluid with the hope that it will spurt fluid to locate the leak instead of the current slow trickle