Just wondering, Has anyone noticed any brand of oil that may help quiet the piston slap at startup on there Chevy or GMC vehicles? Maybe someone has had some luck with a certain oil weight or brand that will quiet this problem .Or is it just hopeless?
Chevy Piston Slap
- Thread starter Red Dog
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A slightly heavier oil might reduce the sound, but oil doesn't solve mechanical problems. GM gets great fuel economy out of it's pushrod motors, but I think that part of how they are doing it is by using a hockey puck sized piston with almost no skirt. I pulled an image for a 1999 Chevy V8 piston from the napaonline site for an example:
Combine that design with less than stellar control over manufacturing tolerances and less attention to design detail than Toyota or Honda and you get an entire family of engines which is very prone to piston slap. It kind of puts the question to the idea that GM and other US makers have finally gotten quality and durability religion
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Look at the typical Honda piston below and you will see that the skirt material is around the entire piston, including the area below the wrist pin. GM's piston has no support below the wrist pin.
Combine that design with less than stellar control over manufacturing tolerances and less attention to design detail than Toyota or Honda and you get an entire family of engines which is very prone to piston slap. It kind of puts the question to the idea that GM and other US makers have finally gotten quality and durability religion
Look at the typical Honda piston below and you will see that the skirt material is around the entire piston, including the area below the wrist pin. GM's piston has no support below the wrist pin.
You could possibly go with a good 5w40 oil like Mobil 1 TSUV. It quieted down my engines and is sold at Wal Mart in the gallon jugs for around $24. See what other users recommend but that is what I would try. Best of luck.
I meant to say M1 Turbo Diesel Truck 5w40 as that is what I use in my Volvos and not the TSUV version. Sorry about the confusion as I was getting the two mixed up.
The only real cure is different pistons with longer skirts like wgtoys pointed out. I'm thinking since piston slap occurs at start up; an oil with a heavier cold viscosity like SAE30 or a 10W-40 might minimise the problem.
Try some Redline 5W-30 or 5W-40. This oil has always been fantastic.
Oil isnt the issue. It is the short skirts. You may be able to "mask" the noise with something thicker....but never eliminate it in my experiance. I just blew mine up (LS1)and dropped in a LQ9 iron block with Mahle pistons...that fixed it
Quote:
Oil isnt the issue. It is the short skirts. You may be able to "mask" the noise with something thicker....but never eliminate it in my experiance. I just blew mine up (LS1)and dropped in a LQ9 iron block with Mahle pistons...that fixed it
I agree with you!
But I'm practical, [ lazy and cheap]
If an oil like Redline might quiet things down why not give it a chance?
Whether it merely masks the noise ...or whether the basestock oil and additives in Redline might also help, I find that Redline behaves like one oil grade thicker and engines run smooth and quiet with Redline.
For example: Redline 10W-40 ran much smoother and quieter than Mobil 1 15W-50 in my BMW's and VW VR6's.
If Redline isn't your cup of tea, then maybe a thicker oil and some friction modifiers like in Valvoline Synpower Oil Treatment.
I can tell you from experience with my 3.4 GM slapper that the absolute best oil for virtually eliminating the slap is Castrol GTX Startup. A very close second is Syntec Blend. (I haven't tried Syntec).
I'm assuming it's the polar esters in these oils that cling to the cylinder walls and pistons and cushions the piston rock that causes the "slap." Whatever it is, it works--at least for me. I can start my van up on even the coldest morning with little to no slap. And in warm weather there is zero slap, period.
I'm assuming it's the polar esters in these oils that cling to the cylinder walls and pistons and cushions the piston rock that causes the "slap." Whatever it is, it works--at least for me. I can start my van up on even the coldest morning with little to no slap. And in warm weather there is zero slap, period.
Hey G-Man, I have the same 3.4 slapper in my van. what weight gtx is that your using?. I would rather use a dino, I was tempted to try the 5w40 that most are recommending but my 5.3L. in the truck has 148k and was thinking the synthetic might cause some leaky seals. these engines have seen nothing but dino there whole life.
Knock knock...who's there?
Grrrrrrrrrrrrrrrrrrr
Do a "Google." Piston slap HAS to be pervasive for so many sites to mention the problem.
Ol GMan beat me to it. Running a maintenance dose of AutoRX is about the only thing I have seen that "cures" or at least minimizes piston slap/
One thing that should be said here. The slap is not indicative of a "malfunction"...these engines perform very well and last as long as competitors V8's....just a nuisance and not a malfunction or poor build.
One thing that should be said here. The slap is not indicative of a "malfunction"...these engines perform very well and last as long as competitors V8's....just a nuisance and not a malfunction or poor build.
From the pistonslap.com site:
-Piston slap is nothing new to piston driven internal combustion engines and compressors. It is the secondary (sideways or perpendicular) movement of a piston against the side of a cylinder bore where the primary movement of a piston is intended to be parallel (up and down) to the cylinder bore. All piston driven internal combustion engines and compressors have a certain amount of piston slap.
Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.
In the case of the famous GM piston slap engine defect, the piston design with hypereutectic (high silicon content aluminum alloy) pistons, reduced or eliminated piston skirts (to reduce reciprocating mass), and a higher ring pack to reduce unburned fuel mixture on the sides of the piston crown have made piston to cylinder bore fit much more critical. The amount of tolerance (variation or margin) in allowable clearance between the piston and cylinder bore to prevent audible piston slap has been reduced by a factor of at least 50%. Consistently hitting the narrower margin for piston to cylinder bore tolerance has not happened for GM during mass production. Thus, some engines have no audible piston slap and some have piston slap on only one or two cylinders. What might have looked really good in testing of hand built engines in the lab hasn't transferred to the production line of this corporate giant.
Make no mistake about it, while a lot of these engines don't appear to be driving rods through the blocks, the ones with louder and longer duration piston slap will wear out before the ones that are basically quiet. The perpendicular heavy impact of the piston against the cylinder wall over time will not come without a price. This is also why GM has released a recent TSB saying that opening 4 quarts of oil to add to your crankcase between a 7,500 mile recommended oil change interval (1 qt per 2K miles on an engine with 36K miles or less is "NORMAL". After 36K miles, all bets are off (there is no abnormal oil usage rate). This is why the now common offer of an engine component letter extending your warranty to 5 years or 100K miles is basically worthless. If the piston isn't laying in the oil pan in pieces, the engine will be operating "NORMAL" according to GM.
For further proof related to the damage audible piston slap can cause, you only need to look at the GMs own TSB # 01-06-01-005. GMs own illustrations will show you.
-------------------
The noise called piston slap is caused by one or more pistons having too much clearance between its side skirt and the cylinder walls. In effect, the pistons become too small and wobble in the cylinder bores. It can be cause by an engine simply wearing out (not common any more), a piston seizing because of a lack of lubrication (it runs out of oil) or it's put together wrong. This is easy to check and usually it doesn't happen to all the pistons. But there could be other causes, none of which could be caused by a "wrong" oil filter. Find out what brand oil filter your shop uses and call its service reps and tell them your story.
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.
-Piston slap is nothing new to piston driven internal combustion engines and compressors. It is the secondary (sideways or perpendicular) movement of a piston against the side of a cylinder bore where the primary movement of a piston is intended to be parallel (up and down) to the cylinder bore. All piston driven internal combustion engines and compressors have a certain amount of piston slap.
Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.
In the case of the famous GM piston slap engine defect, the piston design with hypereutectic (high silicon content aluminum alloy) pistons, reduced or eliminated piston skirts (to reduce reciprocating mass), and a higher ring pack to reduce unburned fuel mixture on the sides of the piston crown have made piston to cylinder bore fit much more critical. The amount of tolerance (variation or margin) in allowable clearance between the piston and cylinder bore to prevent audible piston slap has been reduced by a factor of at least 50%. Consistently hitting the narrower margin for piston to cylinder bore tolerance has not happened for GM during mass production. Thus, some engines have no audible piston slap and some have piston slap on only one or two cylinders. What might have looked really good in testing of hand built engines in the lab hasn't transferred to the production line of this corporate giant.
Make no mistake about it, while a lot of these engines don't appear to be driving rods through the blocks, the ones with louder and longer duration piston slap will wear out before the ones that are basically quiet. The perpendicular heavy impact of the piston against the cylinder wall over time will not come without a price. This is also why GM has released a recent TSB saying that opening 4 quarts of oil to add to your crankcase between a 7,500 mile recommended oil change interval (1 qt per 2K miles on an engine with 36K miles or less is "NORMAL". After 36K miles, all bets are off (there is no abnormal oil usage rate). This is why the now common offer of an engine component letter extending your warranty to 5 years or 100K miles is basically worthless. If the piston isn't laying in the oil pan in pieces, the engine will be operating "NORMAL" according to GM.
For further proof related to the damage audible piston slap can cause, you only need to look at the GMs own TSB # 01-06-01-005. GMs own illustrations will show you.
-------------------
The noise called piston slap is caused by one or more pistons having too much clearance between its side skirt and the cylinder walls. In effect, the pistons become too small and wobble in the cylinder bores. It can be cause by an engine simply wearing out (not common any more), a piston seizing because of a lack of lubrication (it runs out of oil) or it's put together wrong. This is easy to check and usually it doesn't happen to all the pistons. But there could be other causes, none of which could be caused by a "wrong" oil filter. Find out what brand oil filter your shop uses and call its service reps and tell them your story.
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.
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FWIW, the majority of these "slapping" engines don't use any oil in 7500 miles. I've seen lots of them in the dealerships.
The slap goes away after the engine gets warm and the piston expands. I've never known anyone that had any problems from it.
Now you do
On my 2001 Malibu (3.1L V6), piston slap was still present 5 minutes after the engine was started.
The fix was to install new pistons which had teflon on the piston skirts.
Once they had the engine torn down and checked the clearances, they discovered that the slapping had damaged the #2 and #4 cylinder walls and had taken them out of spec.
I got a new motor out of it.
The motor only had 25,000 miles on it when it was replaced.
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