Engine knocking, but UOA shows nothing

[Maddix]

Hi everyone this is my first post. My wife's car is an 02' Nissan Altima with the 2.5 four cylinder 5 speed. It has 86k on it and has started making a knocking sound thats new that goes away after the engine fully warms up. The knocking sound is at RPM'S of about 2500 up. My brother told me to get a UOA done so I did from blackstone labs and they said the engine wear was low. Iron was 6, aluminum was 2, no tin and 1 copper. The sample was taken at 2800 miles using Kendall 5w30. I've tried using purolater, carquest and supertech oil filters and a few different 5w30's with the cold knock still being there. I took the car to a nissan dealer and they said the noise comes from the engine and might be piston slap and might go for 200k like that. What could it be?

 

[Dick in Falls Church]

Piston slap, and it might go on for 200K like that. Same answer you'd get for the same problem in a GM.

You might try a good synthetic--might pump up a bit faster so your noise wouldn't last as long.

Or, you might put on a pre-oiler, which could possibly reduce or eliminate the noise.

Otherwise, turn up the radio and drive on.

 

[Dave H]

I have noticed in my 97 Maxima that certain oil filters "allow" this noise to happen after sitting over night. When I use the Nissan OEM filter (15208-9E000 for mine) or Purolator Pure One it doesn't do it. This may or may not be your problem, but may be something to look at. When you used a Purolator filter, was it the standard one or the Pure One? I don't know if the anti-drainback valves are different between the two or not.

I used Mobil 1 5w30 for two oil change intervals, and it made my engine seem louder than Castrol GTX 5w30 does. Others with Nissan VQ engines have noted the same. I don't know about the Nissan 2.5. My wife's '88 Nissan P/U with the 2.4 runs the same no matter what you put in it, both 10w30's and 5w30's. So it gets GTX 5w30 so I only need to have 1 type of oil on hand.

This oil change (within the last two weeks), I used GTX 5w30, and added 1 bottle of the Valvoline SynPower Oil Treatment (commonly referred to as VSOT on here). It gets good reviews on here, so I decided to try it. My engine definitely seems to run even quieter now. I wasn't going to mention that observation until I had more miles on it so people wouldn't say it is just in my head. Do a search for it on here and you can read other people's experience with it. Might be worth a try for you.

Dave

 

[Gary Allan]

Is it really 'knocking' or are you reporting HLA noise (hydraulic lash adjusters)

They usually don't make noise that you can hear at higher rpms though. It usually happens when cold at idle ..then goes away when warm (sometimes gets worse when warm).

Most knocking that I've observed, that would be assigned the term "piston slap", was under load while cold. It didn't seem to be altered by rpm.

I would also recommend trying a synthetic oil for at least one OCI just to see if this is a flow/visc related issue. If you see the condition shorten in duration ..then you're looking at a cold visc issue.

I've used VSOT in my ticking 170k+ 3.0 Mitsubishi. I must admit that over the couple of thousand miles that it's been in ... that me HLAs have become quieter. They still tick ..but they're not as pronounced at idle. Auto-Rx eliminated all of the really loud ones ..but age surely had taken a toll on all of them.

Your wife puts a decent amount of mileage on there. 86k for a 4 model year old engine is in the frequent flyer catagory. It wouldn't be a waste to do an Auto-Rx treatment just to assure that there are no "unclean" issues with it. Can you tell us how it was maintained and if it was bought new?

Please post your UOA in the UOA forum.


..and

 

[Mike_dup1]

fyi

quote:

---

Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless, but it is the source of piston slap in most all situations.

To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.

Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.

Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.

Unfortunately, when the performance or fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.

The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.

It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.

---