My 2004 Infiniti G35 with 123,000 miles on it overheated on my way to work. I saw white steam coming from hood, immediately pulled over, and head 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?
The cylinder head gasket has a lot of stuff going on. Oil and coolant flowing through it, across the head gasket. Air coming in, exhaust gasses going out. If the gasket fails, coolant can go into the oil, oil and can go into the coolant, exhaust gas can go either into the coolant, into the oil, or into the intake air stream. All and all a bad head gasket, it’s a bad situation.
To test a head gasket a shop could test for exhaust gas in the coolant. Or coolant in the oil. Or oil in the coolant. Or could test to see if compressed air in the cylinder can leak out at TDC (it shouldn’t as the valves are closed and there should be not paths to leak through the head gasket if it is holding. There are other ways too, but those are common ones. The mechanic may simply be hearing a noise, and can tell from experience it is a head gasket leak.
But you as a customer have a perfect right I think to ask him what measurements or observations he’s made makes him believe this is a head gasket problem.
It is very common for a head gasket to fail when the engine overheats. I expect he knows what he is doing. The prices he’s quoting for fixing it seem reasonable. I’d ask him to remove the cylinder head and see how bad the problem is. If it’s not too bad, I’d simply have the surface flattened out and reinstalled w/a new gasket. Sometimes the problems you know you’ve got are better than the problems you don’t know.
With overheating involved, a compression or leakdown test is always the first step before replacing any cooling system parts and running up a bill.
Based on replacing multiple cooling system components without even doing a compression test as a means of checking for a head gasket fault and having to take the car elsewhere for a diagnosis tells me that you need someone else working on it. This kind of stuff is Mechanics 101.
Overheating often leads to piston ring problems. This means if you replace the head gasket you may end up with an expensive, oil burning engine so a head gasket replacement is an iffy repair.
A dry and wet compression test can reveal pretty quickly if there are any ring problems.
The snag here is the resale part of this. As it sits the car has way diminished value and if the engine is changed out then you get into the area of does the resale price justify the repair costs.
There’s also the issue of hoping that any used engine does not have its own set of problems.
The 75k miles engine you mention may have also been overheated or never had the oil changed more than twice. It’s a real coin toss.