Hi. I am in the same predicament. I have a 2015 murano 47k miles. Engine filled with sludge. Perfect service records with all oil changes required. Nissan said I need a new engine for $11,500. They have AWFUL CUSTOMER SERVICE. Never again...
Commenting because I see you replied only half a day ago. I’m in this same situation with a 2012 370Z. Bought the car used with 64k miles, threw a cam pos sensor code and wouldn’t stay out of limp mode by the time I got it home (3 1/2 hours later). Took it to Nissan, who told me the engine was sludged, and I’d need a replacement ($5,000 for an engine with twice as many miles as mine), or they could try to clean it (but they assured me it would never run the same again).
Let me just say, if Nissan tells you this, don’t believe their bullshit. I got the car back as my uncle wanted to do some investigating. He found the cam pos sensors were replaced with aftermarket sensors that didn’t fit the same as the OEM sensors. About $150 later, the sensors were replaced and she ran great.
This isn’t to say Nissan was wrong about the sludge - I did an engine flush and a couple oil changes, and it did seem to clean out lots of sludge. The car blew a lot of exhaust smoke afterward until I found a PCV valve was so gunked up you could no longer shake it and hear the internal components rattling around. I replaced both, which helped the issue, but a week later it began to misfire due to a spark plug being fouled. I took it to a shop who ran a compression test on the cylinder with the fouled spark plug (which came back great) and changed them all out for me. Now I’m seeing a lot of improvement in the smoke, and I suspect after my next oil change it may disappear completely as my oil is already quite dirty. I believe sludge is still being loosened and mixed into the oil, especially as the valve cover and oil pan weren’t manually cleaned. The shop I took my car to said they have seen a Pathfinder do this same thing because of sludge build up in those areas, and after cleaning (and replacing the valve cover gasket), the problem stopped. The dealership planned to do that had I let them proceed with cleaning the engine, but since they tried to make me believe my engine was toast, I decided against letting them touch anything further.
Long story short - these engines are very reliable. Your issue is likely not catastrophic. I think my car has needed TLC for awhile. The shop which changed my spark plugs told me the strut bar appeared to have never been removed. The dealership tried to convince me they were sure a previous owner had gone 20k miles or more without an oil change. The fact they even said that to me with such confidence despite knowing no history of the car tells me it was a scare tactic.
FUCK the dealership, just do as much maintenance as you can, and if nothing works or your problem worsens, then look into more expensive options. My car went from blowing awful smelling blue smoke almost every time I fired it up and after short periods at idle to now, which is that I hardly see any smoke at all except a bit after a cold start. Also be sure to keep an eye on your coolant and oil levels.
Hope my story provides some insight into your issue - it’s been an extremely frustrating month dealing with this. I have faith your engine will be okay.
