Piston slap and oil question, part II

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HACCOFFICER

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Can't find my old post. anyhoo. Basically I ran dyno juice 10w40 to flush my engine after a gasket change and it was quiet as can be. Put the amsoil 5w30 synthetic in the piston slap was back. So after a post here I decided to run a little thicker to try to get rid of the engine noise, mostly the piston slap. SO I buy and put in amsoil 10w30, same noises are present, maybe more. I just dont understand the deal. I would have thought synthetic would be a better oil. The engine it quiet when it warms. However piston slap it present until the engine reaches 130F aprox. There was no slap with shell 10w40 dyno juice. I am lost.


If I have to go back to dyno, can anyone recommend an oil that would have close to the antiwear and other properties such as the synthetic has. Anyone have any expert advice for my situation?


Car is a 1999 Olds cutlass with the 3100 V6, 52K miles.
 
Then again, a 10W40 dino starts out and for a while remains quite a bit thicker than a regular 10W30, and if Amsoil, like Mobil 1 runs a bit light , it may indeed be that your engine wants a pretty thick oil, at least if you want it quieter.
 
FWIW, piston slap isn't always inherently deadly. Engines can often do it for many tens of thousands of miles and have a pretty normal service life. The heavier oil is just masking the noise not repairing the problem... not that making the noise go away to settle one's nerves is a bad thing! I'm just trying to help relieve of of the teeth-grinding anxiety that comes when you hear the noise.May I suggest your favorite CD in the changer and that you crank 'er up!
 
GM Does claim it doesn't damage the engine. I've heard others say the same. However it sounds aweful when it starts. Very embarrasing. I have no problem going back, however if I do i need to find a good oil that will have great anti-wear capabilities. I bought this car two months ago, and need her to last the length of the loan, which is 58 more months. Thats why I bought Amsoil cause of there various tests and they seem to have outstanding wear protection. My friend said to pop some synthetic 20w50 in, I thought that was maybe too thick.
 
i have firebird 92 v6 3.1 112500 miles on it.my car also makes piston slap or valve lifters noise i dont now sure yet.im going to take my car in a next months maybe april,to car mechanic and he can try to found out is the noise piston slap or valve lifters clanking.when i got the car about two years ago.there was nothing wrong in the engine no knocking no piston slap noise or anything.and i think that oils were shell helix plus 10w40 synthetic blend.and i change the oils to mineral 15w40 ac delco.it was okay the first time when i use it,but second time when i change my oils to 15w40,i put in new oils new filter and then i started the car.no knocking,but after two minutes or so,i heard: knock,knock,knock,knock,knock noise coming from the engine so i used that oil couple months and put new oil in:this time .76. 10w40 mineral. still knocking but maybe not that loud.later i have been using gm 5w30 and 10w30 minerals oils and it hardly even knocks anymore.but im gonna maybe change those oils back to shell helix plus 10w40 synthetic blend and see maybe that sound goes away for good.because i got service tickets from prewious owner and the papers were written couple times shell helix plus.and the prewious owner had the pontiac about 12years, so i think that he have been using that shell synthetic blend all the time.but i found out later when i put shell oils back in.hopefully engine is quiet then.i just hope that 10w40 would not be too thick oil or anything.and if the prewious owner really has been using shell synthetic blend it has work in my car very well.because when i drive my car about 3000miles,i only have to add about 1/2 quart new oil and then dipstick shows full again.and that 20w50 might be too thick oil but its your choice what you want to use.
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BTW, many full synthetics run thinner in cold weather than a similar advertised vis dino can. That cold weather flow performance is one of their strengths. You were likely running a thinner oil on start up with the synthetic. So it's no surprise the slap was more audible on a synthetic.

Remember that the advertised grade of a multi-vis oil is based on just two temperature points, and viscosity is not linear across the temperature spectrum. That is why some 10W-30s flow better than some 5W-30s at intermediate colder temperatures. So you just can't rely on the advertised viscosity to know how thick it really will be at your cold start temps.

Bear in mind that piston slap on a cold engine during warm up is rarely a serious mechanical concern. But it can be annoying.

As you surmised, switching to a higher vis oil can mute slapping a little in some instances, but a viscosity substantially above the manufacturer recommendations presents its own set of start up issues.

I would experiment with some 10w-30 syn-blends on your engine if you want to quiet the slap. That will still give you the lion's share of the benefits of a full synthetic.

Again, you want an oil that is a little thicker when colder to quiet the slap. That usually means a dino. But remember that the oil can never flow fast enough at start up if you want reduced wear.

If it were mine, I'd just put in the full synthetic 10w-30 of your choice and live with it.
 
I hate the noise of piston slap, but its the wear I am worried about. I need the car to last the length of the loan. If I knew the piston slap was not damaging my engine I would not even give it a thought. I bought Amsoil due to its anti wear properties in the hopes that a good synthetic would prevent some wear. I spent over $100 on different oils in the last 2 months that I have owned the car trying to get rid of the piston slap. The only thing that did was the shell dino juice. My only thing about using it is that is isn't as good at reducing wear and tear as synthetics.
 
change the Shell every 3k and be happy, Olds V6 will outlast your interest in it
throw in 8oz of Valvo. VSOT and put it on a diet of FP and LC...engine will outlast transmission

have you tried Chevron Supreme or Havoline in 10w40? both quality dino fat oils with lots of antiwear components...
 
Has anyone tried straight SAE 30 to solve this "problem"? Seems to me you'd get all the cold start thickness you'd ever want, combined with an SAE 30 for economy when the oil (and the pistons) warmed up, while staying away from the wide spread 40's and the added VI.
 
Piston slap is normally nothing to worry about. Medium and large diesels have cold start piston slap. Most 2 stroke engines (which rev very high) have piston slap all the time, some worse when warm. I'm not really familiar with the modern GM V6's, do they used forged pistons? These typically are a little loud until the temperature equalizes.

Regardless of what oil, I would run the engine easy until pistons and liners are up to temp. Running it hard cold will dramatically increase skirt scuffing and will really beat up the bore. Pulling the heads and checking cold clearance is the only definite way to tell if the piston slap is acceptable or not. I probably wouldn't worry too much, but I haven't herd this car start!

Patrick
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Why not try Amsoil 15W-40, 10W-40, or 0W-40 varieties? It seems to me that your comparing apples to oranges.
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If u not need the latest edge of fuel economy then just use 15w-40. I dunno if u not already did, but take also a look to the Ester based oils such as Motul and Redline for example.
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