Cold piston slap, thicker oil?

[aquariuscsm]

Originally Posted By: Torino
I converted it over to Mobil 1 20-50. Been quiet for 100,000 mi.+. This is in Las Vegas where COLD weather is rare. John--Las Vegas


Are you using the Mobil 1 V-Twin 20W50 motorcycle oil?

 

[wolfc70]

If it truly piston slap, no oil will help much. There is no pressurized oil on the cylinder walls. Once the piston heats up and expands the noise goes away.

My EX GF's Subaru Forrester slapped like crazy when cold. Car ran fine and had 150,000 miles on it back then.

A friend has a 2000 Silverado with the 5.3 and sounds horrible when cold. By far the loudest piston slap I have heard. It sounds like there are elves with hammers pounding on the block. He tried to get GM to replace the engine under warranty, but they refused. 200K later it is still knocking away.

I would go with the recommended oil weight. Why risk starving the valvetrain (and other engine parts) of oil during cold starts to possible dampen a noise you can't ever get rid of without an engine rebuild.

 

[SteveSRT8]

Originally Posted By: wolfc70
A friend has a 2000 Silverado with the 5.3 and sounds horrible when cold. By far the loudest piston slap I have heard. It sounds like there are elves with hammers pounding on the block. He tried to get GM to replace the engine under warranty, but they refused. 200K later it is still knocking away.


Your friend should investigate carbon build up in the cylinder heads. I've hardly seen a single one of the 4.8/5.3/6.0/6.2 series GM motors with high mileage that did not have some build up.

They are extremely sensitive to this and it sounds just like slap.

 

[4x4chevydude]

youve got it wrong...if its Cold piston slap it needs a thinner oil or lower first number IE 0w if you have a constant piston slap when the motor is running then try a thicker oil or lucas additive, but it will only mask the noise not fix the issue just so ya know.

 

[CBR.worm]

I guess I will just continue to live with it. As someone else mentioned, my first tundra did it until I sold it at 220k miles. It just amazes me how much of a noise difference there is between a 90f cold start and a 40f cold start. During the summer there is no piston slap, during the winter...

I tend to overanalyze and worry about things that I should just ignore.

 

[67Customs]

Originally Posted By: chubbs1
Can you use a 0w30? M1? That is what I would try, I am another who doesn't understand how a thicker oil would stop COLD piston slap. If you decide to go thicker and it helps please let me know, I would be surprised. M1 0w30 or the thicker Syntec 0w30 should do the trick. The Former being my choice, especially since we are getting towards our cold months. I had a neighbor with cold slap and I told him to go thinner and it was gone that day. Never had that issue again.

The 3.7L in my 2005 Jeep KJ has some start-up piston slap. As soon as it gets partially warmed, it goes away. I have tried the speced 5W-30, M1 0W-30 as well as thicker oils like M1 5W-30 HM. None of them make any difference.

I have just gotten use to it.

 

[NutBuster]

PROBLEM SOLVED...

Seriously this is a cheap fix.

I've had multiple slappers. People always seem to think it's incurable or the pistons need to be replaced or re-ringed. I laugh in their general direction.

I've experimented with this, and it's an oil problem. Both of my engines spec'd 5w30, so I stuck with that. Synthetic of any type was generally horrible. The worst that I tried was M1. When I finally decided to save some money one day, I put in regular old Mobil (non-synthetic). To my surprise (and my neighbors) it never slapped again. I bought some Valvoline on sale one fine day for $2 a quart, and it was just as good...perhaps better.

I tried a few others...Castrol, Pennzoil, Havoline...none were as good as the dino Mobil and Valvoline. I've never used anything else in the last 4 years and Haven't had a single slap in all that time...even when the car is left in the garage for a couple weeks.

In summary,
1) stick with the specified weight (or as close as possible)
2) dump the synthetic PERMANENTLY and don't look back
3) install dino valvoline or mobil
4) enjoy the silence
5) thank me later

 

[OVERKILL]

Originally Posted By: NutBuster
PROBLEM SOLVED...

Seriously this is a cheap fix.

I've had multiple slappers. People always seem to think it's incurable or the pistons need to be replaced or re-ringed. I laugh in their general direction.

I've experimented with this, and it's an oil problem. Both of my engines spec'd 5w30, so I stuck with that. Synthetic of any type was generally horrible. The worst that I tried was M1. When I finally decided to save some money one day, I put in regular old Mobil (non-synthetic). To my surprise (and my neighbors) it never slapped again. I bought some Valvoline on sale one fine day for $2 a quart, and it was just as good...perhaps better.

I tried a few others...Castrol, Pennzoil, Havoline...none were as good as the dino Mobil and Valvoline. I've never used anything else in the last 4 years and Haven't had a single slap in all that time...even when the car is left in the garage for a couple weeks.

In summary,
1) stick with the specified weight (or as close as possible)
2) dump the synthetic PERMANENTLY and don't look back
3) install dino valvoline or mobil
4) enjoy the silence
5) thank me later


So conventional oil "muffles" the slap. I don't believe you are the first on here to post about this. The general consensus is that it is harmless (albeit annoying) as per the huge number of GM engines with it that still seem to run forever.

However the actual "fix" for the issue is to get pistons that fit the bores correctly. Since the CAUSE is loose piston-to-wall clearance and short piston skirts, not oil choice.

 

[dparm]

Oil does not fix a mechanical problem -- in this case, a piston that is not the correct size.

 

[NutBuster]

It's not a mechanical problem. It's a lack of lubrication. If your oil doesn't cling to the cylinder bores, some piston designs will tend to "twist" in the bore more than others, creating the slap.

older piston designs with long piston skirts only mask the lack of lubrication. It's unfortunate that some engineers are forced to compromise piston designs to compensate for it.

 

[OVERKILL]

Originally Posted By: NutBuster
It's not a mechanical problem. It's a lack of lubrication. If your oil doesn't cling to the cylinder bores, some piston designs will tend to "twist" in the bore more than others, creating the slap.

older piston designs with long piston skirts only mask the lack of lubrication. It's unfortunate that some engineers are forced to compromise piston designs to compensate for it.


No, it isn't. Piston slap began happening when manufacturers went from hand-fitted bores and pistons to "bulk-fitted" bores and pistons where the block was bored and then pistons "from a bin" were fitted to it. Coated skirts were then added to eliminate the noise, as GM, with the very short pistons they used in the LSx engines was the most affected by this.

If it was a lack of lubrication, there would be an engine longevity problem. Since there is not, it isn't. And if it was a lack of lubrication, it would dissipate immediately as soon as the engine had oil pressure. It does not. It takes several minutes to go away, which is the time required for the piston to expand enough to silence it.

 

[wolfc70]

Originally Posted By: SteveSRT8
Originally Posted By: wolfc70
A friend has a 2000 Silverado with the 5.3 and sounds horrible when cold. By far the loudest piston slap I have heard. It sounds like there are elves with hammers pounding on the block. He tried to get GM to replace the engine under warranty, but they refused. 200K later it is still knocking away.


Your friend should investigate carbon build up in the cylinder heads. I've hardly seen a single one of the 4.8/5.3/6.0/6.2 series GM motors with high mileage that did not have some build up.

They are extremely sensitive to this and it sounds just like slap.


He had the carbon treatment done numerous times when it was under warranty. Once the engine is warm it sounds fine. When cold there are about 5 or 6 pistons that slap badly. It sounds like the motor is coming apart when driven cold! It is a work truck, so it has spent all most all of its life on the highway pulling a trailer.

 

[SteveSRT8]

Good show, at least he eliminated a common issue with these motors. Carbon knock is often confused for slap.

As Overkill stated it's a bad fit and a short skirt simply accentuates it. Mfgrs were simply trying to eliminate friction wherever they could.

We have learned to ignore it. My 6.0 gas engined Savana vans rarely go less than 250k miles before needing anything. We have one with over 400k miles, still a-slappin'!