# Loud rattle at startup



## m3forme08 (Jun 5, 2009)

hey guys

Im new to this forum and ive got a quick question...

ive got an 01 pathfinder and the engine makes a loud rattle-like noise during every cold startup...any ideas what that can be?

thanks


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## underling (Nov 26, 2006)

define the rattle? is it like a metallic tapping from the engine, a loud clacking noise...? More than likely it is just the lifters/valves tapping. Pretty common especially once the engine has worn in a bit. The only solution that really works (or so I have been told) is to have a 3 or 5 angle valve job done so that the valves sit perfectly in their seats eliminating the tapping that you hear. 
I don't know for sure that is what you are experiencing though. A more detailed description of the problem would help. Also, if you are really concerned you can take it to a trusted mechanic. One step further would be to pay to have a scope done on your engine, that would be a last resort though.


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## m3forme08 (Jun 5, 2009)

its a loud clacking noise right at startup sounding like somebodies firing off a machine gun haha..i took it in for a scheduled tune-up a few months ago which completely eliminated the noise, but ended up coming back again :/ I'm hoping its a quick fix i can pull off myself


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## OkcOffRoader (Feb 25, 2005)

try stepping up your grade of oil...the brand new nissan built 3.0 in my 87 does that anytime i go cheap on my oil change....the noise sounds to me like like a dry tap, which goes away in seconds when the oil gets circulating....


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## arknavy (Oct 10, 2009)

My 02 does the same thing. Only on startup, goes away after a few seconds. I also believe it's the valves. I've been using royal purple full synthetic and it still makes the noise. One shop told me it was piston slap, but that's retarded I think. It's getting pretty loud. 

Funny thing is that my 1989 Acura Legend with a 2.7L V6 made the EXACT same noise, but it made it all the time. And I drove it for like 20K miles that way (I know, I'm a terrible person... I'm also broke). 

So yeah, I can keep driving my pathy this way, but I get sympathetic pains every time I start it. Everyone sounds like it's not that big of a deal. Is this true? Don't worry about it?


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## underling (Nov 26, 2006)

The tapping at startup is normal. You can get a 3 or 5-angle valve job which may help. I had heard that the pathfinder suffers from a lower oil pressure which helps contribute to this as well. If it is only on startup then I wouldn't worry about it to much, or have a trusted mechanic listen and give his opinion. My '98 has the tapping only on cold start, once it is warmed up while out and about if I shut it off and start it again there is no tap as the oil has re-coated everything.


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## Platinum_Racing (Jul 6, 2008)

It could be either valves or piston slap.

Valves because of lubrication, and piston slap because of worn cylinders.

If the noise goes away after seconds of running, it's valves. Right at startup it takes a second or two for any significant amount of oil to reach and lubricate the valvetrain. Until this happens they can make a tapping noise. For some reason I've found that valvetrains that use Variable Valve Timing (VVT) that use oil pressure to regulate camshaft timing (Like the VQ35DE) tend to tap more and for longer durations than regular valvetrains during cold startup. A good example is my girlfriends 2007 Toyota Corolla. It has VVT-I and it taps like nobody's business on a cold start, but it goes away after a minute or two. 

If the noise goes away after the car has warmed up it's piston slap. Piston slap is when the piston tilts in the cylinder during the combustion stroke due to the forces on the piston crown of the expanding fuel/air. The piston will literally "Slap" the cylinder, making the noise. When the car warms up and the tolerances in the different materials that make up the internals become more closely matched, the noise goes away.


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## arknavy (Oct 10, 2009)

So it sounds like the clattering valves is no problem. But what about the piston slap? Can that happen on a pathfinder with only 70K miles on it?


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## Platinum_Racing (Jul 6, 2008)

Possible, although highly unlikely. It really depends on how the vehicle was driven. If it was driven hard and sustained high RPM's for a long time it's more likely than if the vehicle was driven within it's powerband. 

Still, 70K miles isn't a lot, even when you consider the GM V6 and V8 engines that suffer from piston slap more often. Those engines, however, can miraculously run for 100K miles or more after piston slap is identified.

I did have a GA16DE suffer from piston slap so bad that it wore down the crown on one of the pistons. (Image below)

This is a piston out of my old GA16DE powered 91 Nissan Sentra. This is a perfect visual example of what piston slap actually does inside the engine. Note how the top of the piston appears to have been "Ground down" by the cylinder wall. Surprisingly, this piston was the only damaged piston in the engine, and it still had the highest compression. The other 3 cylinders had less compression and lower pressure than this cylinder due to worn piston rings. My theory is the tilting of the piston somehow preserved the sealing surface of the piston rings on the compression stroke. This engine died completely at about 155K miles.









The reason why I don't think you should worry about it too much is because the engine isn't even at 100K miles yet, and it has an oil-pressure regulated variable valve timing system. My theory (That I developed to explain the issue in my girlfriends Toyota) is that when the oil is cold and thick, it doesn't operate the timing device mounted on the camshaft sprocket properly... At least not until it warms up and gets closer to the system's designed viscosity.


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## arknavy (Oct 10, 2009)

Awesome. I love pictures. Thank you. Sounds like a good theory about the valve timing control. Do you think that if I installed a block heater that it might keep the oil warm enough to allow the timing device to operate properly? I would only do this because I like experiments


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## underling (Nov 26, 2006)

A block heater is good at lower temps as it keeps the oil fluid and helps ease distribution at startup. You may still get slight tapping right at startup until the oil reaches the valves. Again this is normal and nothing to worry about. It should only last a second or 2.


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## Platinum_Racing (Jul 6, 2008)

The block heater would also prevent the engine from becoming so cold that the tolerances would change dramatically. They don't keep the motor at opearating temp by any means, but they do help.

When my Cummins Turbo Diesel block heater died it wasn't happy at all... But it didn't really complain. My main problem with that truck is the intake heater would always kill the battery.


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