My 2004 Infiniti G35 V6 with 123,000 miles on it overheated on my way to work. I saw white steam coming from hood, immediately pulled over, and had it towed to my mechanic.
My mechanic replaced the thermostat, water pump, and radiator. However, after making those fixes he determined that the head gasket is blown. He hasn't given me a clear answer as to why he thinks this (there are some language barrier issues), only that after making the initial repairs he wasn't satisfied with how it was running and eventually took it to the Infiniti dealership for them to run some test (?). He doesn't have any printed out test results or anything to show me. The mechanic is a friend of a friend, so I don't think he is trying to rip me off, but I want to make sure he hasn't somehow made a mistake in diagnosis.
Questions:
(1) What evidence should the mechanic be able to show me to prove that the head gasket is actually blown? Should I get a second opinion, and if so, how do I go about doing that?
(2) He is quoting me $2,500 to replace the head gasket and resurface the head OR $3,500 to replace the entire engine with a used engine with 75,000 miles on it. At this point, I am planning on making the repairs, then selling the vehicle so I am not out the money. Would it be worth it to spend the extra $1000 to replace the engine rather than just repair the head gasket? In other words, if I spend an extra $1000, will it (a) be significantly easier to sell my vehicle or (b) will my vehicle command a better price than if I were to just make the less expensive repair?
Thank you so much for the advice.