Chevrolet Lumina making a ticking noise below 1000RPM

Question

Hello ladies and gentlemen,

I bought a second-hand car about 2 months ago which started developing a ticking sound from the engine bay. The sound is coming from the top/passenger side of the engine. This ticking sound is only there when the car is idle. It completely disappears when I go past 1000 RPM. I have even tested it in a tunnel to make sure it disappears. This only happens when the car is warm as well. When I start the car in the morning the sound is not there and doesn't come until the car has been driven/warmed for a bit. The previous owner was a very old man in his late 70's and he had no crash/maintenance logs. He never drove the car above 90KM/h when he had it in his possession. When we first bought the car it was near perfect until I pushed it to around 120KM/h a week after we bought it. It started making the sound from that day. We thought maybe the oil is bad so we went and did an oil/oil filter change. The sound went away for around a couple days then came back so we took it to a mechanic. He disassembled the engine and told us what the problem was but I am not a car-savvy person and don't remember what he told us. I only remember him saying that the "Crankshaft" needed changing. Once he gave us the car back the sound had completely disappeared. It stayed like this for around a month until the sound came back around 2 weeks ago. From then we have changed the oil/oil filter twice. Each time the sound disappeared for a couple of days and then came back. I wanted your guy's honest opinion before we have to take it back to another mechanic and get ripped off again.

Info:

Car - Chevrolet Lumina 2007 V6 3.6L Automatic 4-Speed
280,000 KM Mileage
Check Engine light on
Oil being used: Mobil Super 1000; 20W-50 XHP
Link to video of my car:- https://www.youtube.com/watch?v=zMfMyhurojE&t=1s

Recent maintenance - Transmission oil change only because of leakage(Not filter)
A/C compressor electricity wire was loose.

P.S.: I live in the middle east where the temperatures can hit 40C Mid-Day

Update 1: I went to a mechanic who advised me to do an oil change to 10W-30 which is the correct one and drive for a week or two to see if anything changes. After 2 weeks of driving I have found this: The sound will still be there when cold BUT, it completely disappears after driving the car for a minimum of 10 to 15 minutes and that is something which is really confusing me.

I also did a computer check for the check engine light and these are the codes which came up: P0131 - $07E8 - O2 Sensor Circut Low Voltage Bank 1 Sensor 1
P2251 - $07E8 - O2 Sensor Negative Current Control Circut/Open Bank 1 Sensor 1
P0521 - $07E8 - Engine Oil Pressure Sensor/Switch Range/Performance

The check oil light also sometimes comes once in a while but much less than before.

Any Advice?

Answer 1

The noise you've presented in the video is quite a lot more noisy than what I'd consider to be valve train noise. With it going away with you revving the engine past 1000rpm seems to me to be an oil flow issue, where the engine is not getting much pressure under the 1k rpm mark. It may be enough to not trip the oil pressure light, but with the engine wear which is most likely at 280,000km (174k miles), clearances have opened up and now you have noise somewhere in the engine. It is my approximation, you're going to need some serious engine work (a rebuild with new bearings and such) or a new (rebuilt or something with much less mileage) engine. My suggestion at this point is to take it to another mechanic for their opinion ... you may even want to take it to a third mechanic just to be sure. Diagnosing engine noises over the internet is problematic, in and of itself. Don't go spending money on what I've told you, ensure you have someone who can be hands on to give you a more comprehensive diagnosis.

Answer 2

2 things:

• Has the timing chain been inspected? It may be loose and rubbing against the guide.
• Your check engine light is on. Have the codes read with an OBD2 scanner and update your answer with the results.