Trailblazer Oil Question

[Nick1994]

We have a a 2002 Chevy Trailblazer LTZ with the 4.2L I6. It has always been maintained its whole life, 3-4k mile OCI and runs great. I changed the oil myself for the first time at 89k with Castrol GTX 5w30 White Bottle and a Wix filter and at 93k with the same. It now has 95k and each time the oil was changed it didn't necessarily knock, but it was pretty noticeable but was sort of a knock (hard to explain) for the first 5-10 minutes of running on the oil. It then went away and never came back. It runs beautifully, isn't abused, and is in 99% mint condition. My grandparents own it and put 2k on it since I changed the oil in August. What do you think this is, and what oil do you recommend next? Maybe a 10w30 GTX HM?

 

[lynam]

i had a 2002 envoy with the same motor, no matter what oil i ran in it for the first 5mins on a cold start it would knock. It's piston slap and GM says its normal. All most all 4.2 do it on a cold start up dont worry about it.

 

[Clevy]

I'm betting its coming from the bottom end. It like a diesel sound almost until there is some miles on the oil then it goes away.
For example the sound is there right after the oil change and a couple of hundred miles,but then it's gone and doesn't happen again til next oil change.
Is that what you are experiencing?
If so I've learned that its harmless and doesn't affect longevity. It was explained to me as being the bearings and the new oil cleans off the old oils anti-wear layer,then once the new oil applies its anti-wear layer the noise is gone.
That's how it was explained to me. It made sense so I didn't question the idea however that may not be entirely correct,although it did make sense to me.

 

[Bgallagher]

Originally Posted By: lynam
i had a 2002 envoy with the same motor, no matter what oil i ran in it for the first 5mins on a cold start it would knock. It's piston slap and GM says its normal. All most all 4.2 do it on a cold start up dont worry about it.


+1 Wouldn't worry

 

[Doog]

Another GM piston slapper. I had 2 of them. Never again...BTW, there is nothing you can do to stop it. A 10wXX will mask it a bit but not much.

 

[Gabe]

Mine does it too.

 

[tiger862]

Its the sleeves in the piston. GM would replace the engine if you complained enough. I have had to replace many under warranty. There were a couple that sleeve cracked and hit head. Seemed like new ones did same thing after a short while. I always thought piston was to small and would expand after hot but what do I know. GM installed a cast iron sleeve in an aluminum block so different heat points. I know of a few with over 250k but are now having oil pressure problems at idle. I have recommend new engines but they want to patch which I won't do with that mileage.
http://forums.trailvoy.com/showthread.php?t=427&highlight=2002+engine+vin&page=13

 

[JPP]

Originally Posted By: Bgallagher
Originally Posted By: lynam
i had a 2002 envoy with the same motor, no matter what oil i ran in it for the first 5mins on a cold start it would knock. It's piston slap and GM says its normal. All most all 4.2 do it on a cold start up dont worry about it.


+1 Wouldn't worry


+2 on my 2004 TB

JP

 

[ARCOgraphite]

Run an ACDELCO filter and Pennzoil HighMileage 5w30 or QSUD. Our My 2007 Chevy 1500 and recent Subarus knocked like crazy on GTX (the Subaru bulk oil). You can substitute a qt of 5w40 RT6 in with the QSUD ( dont overfill) to quell the racket. Many engines of all types with short slipper skirts evidence piston racket - Dodge, Honda, Suzuki, toyota, GM, Ford, etc - absolutely not an isolated GM phenom. My New Honda sound like a cement mixer with a couple boulders and a roofing hammer in it - I subbed in a 1/2 qt Rotella T5 10w30 to keep things quiet with NO downside.
My experience says stay far away from oils using Sodium addpacks, e.g: Castrol Mineral oils, NAPA Syn and VWB.

 

[Corvette Owner]

Definitely Piston Slap, here is an excerpt from

http://www.pistonslap.com/


Around 1998, GM switched from a "Select Build" method of manufacturing and/or assembling engines to a "Net Build" method, in order to save money on manufacturing and/or assembly. In the Select Build process, pistons and cylinders are matched for size and fit. GM's new "Net Build" method of manufacturing and/or assembly, in contrast, assumes all pistons will fit equally well in all cylinders and does not allow for variations in the size of engine cylinders or pistons. The pistons of slightly varying size (all within spec) are not individually matched with the cylinders of slightly varying size (all within spec).

Excessive “piston slap” occurs because an automobile manufacturer (GM) designs and/or manufactures a defective engine in which the clearance between the piston and cylinder bore is too great. Essentially, the piston moves sideways and “slaps” or “knocks” hard against the cylinder bore and causes damage to the engine pistons and cylinders, excessive smoke emissions, excessive oil consumption, carbon buildup on piston heads, decreased mileage, and a loud and obnoxious “slapping” or “knocking” noise, all of which diminishes vehicle resale value in the trade.

 

[147_Grain]

Originally Posted By: Corvette Owner

Excessive “piston slap” occurs because an automobile manufacturer (GM) designs and/or manufactures a defective engine in which the clearance between the piston and cylinder bore is too great. Essentially, the piston moves sideways and “slaps” or “knocks” hard against the cylinder bore and causes damage to the engine pistons and cylinders, excessive smoke emissions, excessive oil consumption, carbon buildup on piston heads, decreased mileage, and a loud and obnoxious “slapping” or “knocking” noise, all of which diminishes vehicle resale value in the trade.



Excellent explanation / well said!

 

[salv]

My 03 with the 4.2 makes a little noise when first started, but smooths out to whisper quiet in a minute or two. It has run great on Mobil Special 5w30, Havoline 5w30, and really likes the GTX HM 5w30. I have been toying with the idea of running Mobil 1 0w40 in it, being that it is an aluminum twin cam straight six.