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Discussion Starter · #1 ·
Hey guys, I'm really hoping you can help me out as I've exhausted myself reading through countless forums. My mechanic is stumped and told me to wait till it becomes more consistent but I'm worried something sinister is at play.

2008 pathfinder with yd25 auto trans.

Bought at 213000km and has developed a noise that only occurs after the engine has come to temp and only whilst driving, cannot reproduce in neutral. Had it happen just before a red light, put it in neutral, revved and nothing, light goes green, I drive and it happens again.

Consistently happens after about 10 to 15km of driving, persists for about 1km, but then either goes away or gets quieter (not sure which). Only between 2000-3000rpm

Doesn't seem to depend on load either as it happens on flat road as well.

There's no smoke, no loss of power, no misfire.

Please help!
 

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Hey guys, I'm really hoping you can help me out as I've exhausted myself reading through countless forums. My mechanic is stumped and told me to wait till it becomes more consistent but I'm worried something sinister is at play.

2008 pathfinder with yd25 auto trans.

Bought at 213000km and has developed a noise that only occurs after the engine has come to temp and only whilst driving, cannot reproduce in neutral. Had it happen just before a red light, put it in neutral, revved and nothing, light goes green, I drive and it happens again.

Consistently happens after about 10 to 15km of driving, persists for about 1km, but then either goes away or gets quieter (not sure which). Only between 2000-3000rpm

Doesn't seem to depend on load either as it happens on flat road as well.

There's no smoke, no loss of power, no misfire.

Please help!
Welcome to the forum.

Hard one to diagnose remotely.

Does it sound like it is coming from the engine or the transmission?

It could be many things, but one thing that springs to mind as a common fault is the overrun clutch on the alternator. A squirt of wd40 (not on the belt) would quieten it down for a little while. Actually the tensioner pulley on the belt might also be worth looking at, these do wear out.

I assume oil levels in the gearboxes, engine, power steering etc have all been checked?
 

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Discussion Starter · #3 ·
Thanks for the hasty reply.

I did an oil change, fuel filter and air filter about 500km ago, powersteer and brake fluid are good.
Will check trans oil level tomorrow but transmission is smooth so didn't think about that.

Is that what you meant by gearboxes?

It definitely sounds like it's coming from the left side of the engine bay where the alternator is, but again, hard to tell as it only happens when I'm driving.

The noise itself doesn't bother me as it goes away after a short burst.. it's what's causing it that makes me worry.

Yes I've read about the alternator pulley, so will book it in asap to get all the pulleys/belts looked at.

I've also read about issues with an o ring that causes engine oil to drain back into the sump. Every morning when I start it, there's a knocking noise for about 3-5 seconds which disappears once the oil light goes out, the oil light goes off straight away when I start it after work (8 hours later) and no knocking noise. Could this be an oil pressure issue?

Thanks again, for your help!
 

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Yes, get those belts and the alternator pulley looked at.

The knocking could be a couple of things.

When the engine is cold the diesel doesn't get completely burnt, that can produce knocking.

There is a non return valve in the oil filter (it is sideways mounted so oil drains out). Some cheap oil filters may not have this or it may be not very good.
Did it make the knocking noise before the last filter change?

There is also a chance the wrong oil is in there, it should be 5w30, if somebody has put in 10w30 it will take longer to get the oil circulating.
 

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Discussion Starter · #5 ·
I did the oil change myself, I got the filter/oil from supercheap auto based on what their system recommended.

Thinking about it now I did start noticing the knock after the oil change but maybe it was there before. Ryco oil filter so may got for a better quality one next time.

Penrite 5w-40 full synthetic oil (which I just read is similar to 5w-30 but better in hotter conditions, I'm in Australia so it gets very hot here).

I did check the manual and it does say 5w-30, will the 5w-40 be ok in my circumstances?

Thanks again for your help, I will get the earliest booking to get pulleys looked at (massive shortage of mechanics here on the sunshine coast 😢) so may be a week or two before it gets looked at.

Will definitely update and let you know if it fixes the problem.

Cheers!
 

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That oil will be fine.

One thing I didn't think is possibly injector rattle. Most noticeable on a light or slightly trailing throttle at 2k rpm.

If it does it then often injector cleaner in the tank will cure it.
 

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Discussion Starter · #7 ·
So I checked the trans fluid and it appears that it has been over filled, which I've read can cause the type of noises I'm hearing.

Going to do a flush tomorrow and see if it fixes the issue.

The dip stick has two notches below the checkered part, safe to assume that those notches are for when it's cold?

Should be a pretty straight forward job for me? Just tilt the car slightly towards the drain plug and best to do it when it's warm?

I also noticed that the plastic cover on the front face of the alternator pulley was slightly cracked before, and now it's gone... So probably and issue there too 😢
 

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Correct that overfilling the transmission does cause problems.
As far as I know the max/min marks on the dipstick are for when warm.

Drain and refill does leave about a litre, so if you wanted to properly flush then drain and refill needs to be done a couple of times if that is what you want to do. Your method will work.

That plastic cover is just a cover, if the pulley is playing up there will often be a layer of thick residue.
 

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Discussion Starter · #9 ·
So seeing as I need the engine to be at operating temp to measure the amount accurately, what happens if I don't add enough and turn the car on.. will be safe for the transmission so long as I leave it in park?
 

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Discussion Starter · #11 ·
You're a legend, thanks heaps for all the advice.

I've decided to get a mechanic to do a flush and change filter etc.

I'm used to working on '90s cars 😅 everything is so complicated these days.

Booked in for Thursday so will update the thread once I find out if the problem is fixed 🤞🤞🤞
 

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Discussion Starter · #12 ·
Got the trans flush/filter change done.. apparently the fluid was quite brown, so, happy to get that off the check list.

I asked them to have a quick look at the pulley/belt situation and they reckon there's nothing wrong with em.

The noise I'm hearing seems to have gotten slightly quieter and less persistent.

But it still happens after 10km driving, under light throttle, and only in what appears to be 1st and 2nd gear.

I've only done about 50km driving since the flush so maybe the new fluid needs a bit of time to work it's magic.

Do you think this could be a transmission issue?

I'm also getting just over 400km out of a tank which is approx 80L.

I've thrown some injector cleaner in there today, so will see, but I think a tune is in order?
 

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Discussion Starter · #14 ·
Yes, extremely high consumption, 16.8l per 100km at last reading. I've read they are usually about 12l per 100km..

I really don't think the injectors are the issue. But will try the cheaper approach first 😂

It starts up first pop and hauls ass whenever I ask it to, even up steep hills, although I've never had it packed out with gear.

I'll give the MAF sensor a clean and see if that helps. Seems like the previous owner didn't really care for it so there will be plenty of learning to come about.

Thanks again bro!
 
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