Can someone help me?

[Hailsteve]

Almost 100% of the time when my 300zx is running there is this noise that is actually quite loud. it sounds like it is coming from the top left of the engine bay and even the passenger side front fender.

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This is my first post on this site but i have been lurking around for a while. If you could help me identify this odd noise i would be truly grateful.

Thanks in advance.

[MrFeesLaw]

that's a tricky one... definitely something inside the engine if it does it at idle... could be something in the valvetrain. or in the block... could really be just about anything in the engine... Wouldnt be in the trans if it does it at idle... hmm...

Are there any check engine lights on?

is it leaking oil anywhere?

Is there coolant in the oil? Or oil in the coolant?

Having a little more to go on would be really helpful!

[Hailsteve]

that's a tricky one... definitely something inside the engine if it does it at idle... could be something in the valvetrain. or in the block... could really be just about anything in the engine... Wouldnt be in the trans if it does it at idle... hmm...

Are there any check engine lights on?

is it leaking oil anywhere?

Is there coolant in the oil? Or oil in the coolant?

Having a little more to go on would be really helpful!

Everything is working properly. No lights, no leaks.

[nissanfreak12]

That is definitely a bearing noise. Couple questions;

Is it a 5 speed or an Auto?

When you rev it, does the noise go with the rev?

Have you tried to eliminate all the accessory belts? It is ok to run for a short time without all that running, I mean 30sec to a min.

If its a 5 speed, does the noise change when you press in the clutch?

[Hailsteve]

That is definitely a bearing noise. Couple questions;

Is it a 5 speed or an Auto?

When you rev it, does the noise go with the rev?

Have you tried to eliminate all the accessory belts? It is ok to run for a short time without all that running, I mean 30sec to a min.

If its a 5 speed, does the noise change when you press in the clutch?

Unfortunately it's an auto
The noise is only at idle

[nissanfreak12]

Have you check your transmission fluid?

If you put it in drive or neutral, does the noise change?

Is the noise more prominent in the rear or the front?

When was the last time you serviced the transmission?

Checking your fluid needs to be done warm and in neutral. That is when the pump is actuated. If the sound changes, its a transmission issue when put in drive/neutral.

[Hailsteve]

Have you check your transmission fluid?

If you put it in drive or neutral, does the noise change?

Is the noise more prominent in the rear or the front?

When was the last time you serviced the transmission?

Checking your fluid needs to be done warm and in neutral. That is when the pump is actuated. If the sound changes, its a transmission issue when put in drive/neutral.

the transmission is fine, the noise is coming from the top left of the engine bay

[nissanfreak12]

So apparently you know everything about the dynamics of these cars and you don't want help. Good luck

[z.Leinbach]

Hmm. If it's top of engine might be a sticky lifter or a crushed lifter or a failing bearing

[nissanfreak12]

Hmm. If it's top of engine might be a sticky lifter or a crushed lifter or a failing bearing

Sticky lifter or crushed lifter sounds nothing like that, they have a destinct tap, almost a knock sound and WILL go with the rev of the engine. Sounds travel in engines/transmissions. Metal/aluminum have different characteristics of sound. That noise is definitely a bearing issue and where he is hearing it from, back of engine from the top could very well come from the transmission tunnel.

Roller bearings have that sound. When journal bearings(crank, rods, camshaft bearings) make noise they knock because they rely on oil. Oil acts as a ball bearing, when the oil has grooves, its like water, path of least resistance, it goes in the grooves. Now you have metal on metal with too much clearance. This is why it knocks. There are no roller bearings on the top of the engine, just journal bearings. Other than alternator, water pump, AC, Power steering pump, and transmission, which all have roller bearings, there is no way to have that sound from the heads.

Now could it be metal on metal rubbing, like the flex plate on some metal, maybe. But the OP hasn't really dug that deep, yet.

[MrFeesLaw]

that's a tricky one... definitely something inside the engine if it does it at idle... could be something in the valvetrain. or in the block... could really be just about anything in the engine... Wouldnt be in the trans if it does it at idle... hmm...

Are there any check engine lights on?

is it leaking oil anywhere?

Is there coolant in the oil? Or oil in the coolant?

Having a little more to go on would be really helpful!

I want to take back my own post lol. I said it couldn't be the trans if it was doing it while out of gear. I said this because I assumed you had a manual... Should have asked before assuming. Anyways... NissanFreak12 is correct. Sounds carry in an engine bay. I often hear things that people think are coming from the block, and it turns out to be an external accessory that is just bouncing sound off the block. An engine bay is just a big metal box, which gives it great acoustics! This is why we use a stethoscope (you can get them for like $10 at any auto parts store or hardware store), they resist echoes and help to pinpoint exact sound locations. If I had to recommend something I would say get a stethoscope and find, for sure, where the sound is coming from. Would hate to tear apart an engine only to find out the noise was in the trans. No one likes to spend money on diag, but spending $10 now might save you hours of labor and tons of money throwing parts at problems that don't exist.