Nissan Repair: 2010 Altima limiting revs, vacuum leaks, nissan altima

Question
Hi.

I have a 2010 Nissan Altima 2.5S with 20,000km and full dealer service. I'm posted to Saudi Arabia, so it's a local model - but seems pretty much the same as the US model.

After driving fast for a while - say 20 mins at over 5,000 rpm, the engine starts to make a metallic high-pitched whistling noise. The noise stops when revs are dropped a little, but comes back when revs are increased. After dropping revs substantially, they will not increase again and seem to hit a limit at about 2,000rpm (not exact and can vary a bit). This has happened a few times on long free-way runs (300Km plus) between towns here. Stopping is not really an option (bandit country).

After cruising slowly for 10mins or so, the problem completely disappears.

I'm guessing an oil feed deficiency of some sort, but no error lights or overheating. Dealer has checked the engine a few times. Nothing wrong and no error codes (he says).

Fully expecting my engine to fall to bits, but except for long fast runs, everything seems absolutely fine. Full power available and no issues.

Any ideas? Not sure of the dealer standards here and possible they missed something.

Thanks!

Answer
Brian,

I would change to Mobil 1 5W30 synthetic to help lubricate the engine.

The noise could be associated with the intake leaking when the secondary air tract opens.

I will check on recalls and service bulletins and email you back.

Currently, I would be looking for vacuum leaks.