Cold engine knock,what oil should I use?

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Oct 20, 2003
New to this site and there is SOOOOOO much info here. This is my problem. I have a 2000 Z-71 with 5.3L with 58000 miles on it. Gm has a problem with cold engine knock and im wondering what oil should i use to try to solve this problem. Been using Mobil 5-30, Last winter i was using Shaffer oil for cold weather starting with Moly. Now with my Knocking going on,what do you think i should use to make this motor last till 120000 miles when im up for a different truck.Like to here your input,THANKS
I hear a lot of startup knocking sounds with Mobil 1. Try Pennzoil 5w-30, Chevron, Or Amsoil. The dilemma is that the piston, when cold, has too much room to move inside the cylinder of the engine. With extra room the piston slaps the side of the cylinder wall, which results in a knocking noise, until the piston and cylinder warm-up and reduce the room available for dancing. I could be off-base here, but in a situation like this, I believe the only way an oil could help would be for it to be of a higher viscosity compared to what you're currently using, placing a thicker hydrodynamic-barrier between the piston and the cylinder, thus possibly reducing noise until the engine warms up. 5w-40 15w-40 Even M1 15w-50 Could also try the trick I talked about earlier. On startup, floor the gas pedal for a few seconds. Then, let up, and the engine will fire. While this won't supply a huge amount of fluid-lubrication to the engine, it could help your situation a little. [ October 21, 2003, 11:15 AM: Message edited by: Jelly ]
Can I suggest the Brew which is a 3:1 ratio of Schaefferss #132 mixed with Lube Control. The $132 will slightly increase the viscocity of the Mobil 1 and may help the slap. I use this in one of my cars with Amsoil 0W30 and it reduced the slap considerably. 6 oz of 132 to 2 oz of LC at oil change. Or, just try the Schaeffers 132 and see.
I have a 2001 Malibu with the 3.1L piston slapper, After trying many different types of oil to quiet the noise here is what I have found. Synthetic in 0,5,10w-anything makes no difference and in fact it was the loudest using these oils, 10w-30 regular pennzoil was the best at keeping it quiet but the motor seemed to be "sluggish" on this oil. After reading everything I could find on this Board about Piston Slap it seemed that Moly was the key to help squelch the knock, It seemed like Redline has the most Moly but I wanted to be able to get the oil I use at Walmart and not have to order it. The mixture I hit on which has completely quieted my Piston Slap is Pennzoil 5w-30 and Valvoline Max Life engine protector in the red bottle, according to its voa on the Valvoline it has lots of Moly. This mixture has been working great for over 4 months with 2 oil changes and 8k miles, I also have always used Wix oil filters with the red adbv. I use one whole bottle of the Valvoline, I think it is 8oz's and the rest Pennzoil 5w-30, the whole oil & filter change costs about $17.00.
Thanks for all your comments. Im due for a oil change in another 1000 miles. I never knew Mobil oil ran on the thinner side,i might have to try the Pennzoil with the extented life in it. Thats why i was looking at Shaffer oil because it has moly in it. A guy at work sells it and i can get my hands on it from him.I might end up trying both and see what happens.I might send it both end after im though with it and get it checked to see which one wears differently.Thanks again for your comments.Love to hear what people have to say about different things that they have tried.
How long does the "cold engine knock" last for? Why does everyone think it's piston slap? Why not a stuck valve/lifter? Is this question timely because of the colder temperatures, or are you getting this knock in July?
I always heard the noise and really never thought it was piston slap,I to thought it was a lifter or a fuel injector.Then i was on a site and they were talking about piston slap in the GM from 98-02 and i went to the sight and then i relized that was the noise that i was hearing.It is louder know then in summer months because of the temp getting lower.Thats why i was asking about oil,i go up north to ride snowmobiles and it does get cold and i hate to start my truck up and hear that slapping away.I know i can never get that noise gone without a different motor,but i know oil will help it alot with it banging away.It does go away once it is warmed up,just thinking what oil will get there faster and with less wear on the banging
I have a 2002 GMC with 5.3 with 12000 miles. I have heard the slapping noise once, it happened the morning I changed oil from 5w30 Castrol Dino (what ever the dealer used at 7500) to Walmart 5W30 blended. I haven't heard it since.
I have the same truck with a little more milage and a bit of the 'ole piston slap. I've used 5w30 M1, 5w30 Formula Shell, 5w30 Pennzoil Multigrade, 10w30 Pennzoil Multigrade and finally 0w30 Petro-Canada Duron XL, even in the summer. The best result so far as reducing the annoying slapping sound has been the 0w30 PC Duron XL. the pennz was OK, but I didn't think there was enough oil pressure when it got hot, better pressure with the Duron. I haven't done an analysis, don't really want to know about my problem I guess. I think it's critical to get oil on the cylinder walls as quick as possible to reduce the audible sound of the slapping. It probably still occurs ut is dampened by the oil.
I'd just go 5w-30 in the dino oil of your choice for winter, and 10w-30 in the dino oil of your choice for summer. I had a Grand Am with a terrible slapper using Mobil 1, and dino quieted it down considerably. I wish you guys could have heard that motor. It was worst when you had driven for a while, shut it off, then started it again after about 1.5 - 2 hours. It was 4 times as loud as any motor I've heard with rod knock, and I was riding in my buddies turbo Celica with a rod knocking and it eventually siezed the bearing and punched a hole through the oil pan. That wasn't even as loud as my Grand Am on occasion [Eek!] My car must have been seriously defective; like some of the LS1s that came with mismatched pistons to their particluar bores.
[Welcome!] I agree with the previous posts, that this is a design problem, not oil. However many people get long life out of these engines. M1 5w-30 is a very thin oil. Try another brand like Amsoil or Redline or try M1 0w-40. Bascially the knock will always be there, but you can hide it with the right oil.
The question is, does this piston slap reduce the life of the engine? I'm not convinced that it hurts anything, but if your looking at a thicker oil especially in winter you could be causing undue wear on bearings and cams. If it were me, I'd stick with the 5w30, but a remote starter on your truck and start it 5 minutes before you drive off, I bet you will never "hear" the piston slap again.
I am switching back over to Mobil 1 0-30 this week and taking out the Mobil 1 10-30. The 10-30 has been fine in the summer but now that the temps are getting colder, I definately hear more start up noise. Last winter even at sub-zero temps with the 0-30 the noise only lasted 5-10 seconds. Consumption has been the same with either the 10-30 or the 0-30.
The CSK noise is something you are going to have to live with. I know of several guys with GM trucks with over 100,000 miles and their engines have never broken down. One guy has a 1999 and it made that noise within the first 10,000 miles and still to this day. Does not use oil and running strong. He sells insurance and logs over 100+ miles daily. He told me its the best truck he ever had and his company has had Ford and Dodge. They buy all brands because they have dealers as customers. I think there are 2 things going onl some engine have piston slap as described and some engines just make noise due to disimilar metals in the engine which expand at different rates. I have heard the noise and if its pistons, why do you hear a knock noise about 1-3 times a second when the piston is moving some 70 time per seconds? I had a 1990 V6 Lumina, a 1993 Lumina, 1999 Monte Carlo Z24, a 2001 GMC and each one has made a noise when cold that disappears when the enigne warms up. As for the noise being helped or eliminated by a particular brand or weight of oil. That is wishfull thinking. The service manager of a local GM dealership whom I have known well for over 20 yrs told me they have tried all the different oils etc and will some seem to imorove it, it only last a short time and the noise is back. He also said that he has seen trucks exhibit the noise and then not make a sound for miles and miles, then start at it again. There are some theroies that the noise is the result of carbon forming on the pistions, when cold a noise is made by the interaction with the engine firing and the carbon. I know some strongly disagree with this and claim it harming the engine yet the amount of engines failing from this is small. Actually those engines that have been rebuilt or replaced have the same noise. This is my opinion, right, wrong or indifferent. I own 2 of these GM engines, 2001 5.3L and 2002 5.7L LS1
As for the noise being helped or eliminated by a particular brand or weight of oil. That is wishfull thinking.
No it's not, it's common knowledge on here that a thicker oil will make an engine sound quieter and smoother, simply because the thicker oil cushions the sound. It's obviously not fixing the problem mechanically, but it's making things more pleasant for the owner since he won't hear the sound as much. Lots of guys with piston slap on have reported quieter engines after switching to a thicker oil. Are they all just imagining it? [I dont know]
Well we have tried it and it has not worked. My buddy has one of these trucks and he has tried it all up to 20W-50 and the noise never improved on bit. He went back to using 5W-30 like oil filler cap said. I tried 20W-50 for about 3 months and now have 10W-40 in my 2001 5.3L GMC for almost 6 months/7,000 miles now and there was no change in the cold start noise at all. But there are times when it never makes the noise, how can that be explained? For instance I was passing a truck hauling a loader and kicked the 5.3L into passing gear and took off, running it from about 35mph up to almost 80 before backing off. I noticed it was pinging hard so I kept it floored and when I looked to see to pull in, I noticed what seemed like dust coming out of the tail pipe (blowing out the carbon?). That was on Monday and to this day I have used the truck each day, logged about 150 miles and the engine has not exhibited the cold start noise while it was every am for months, even in warm weather. Has me wondering if carbon is the problem. The cloud out of my tailpipe was like I never seen before. Truck just turned 39,000 miles.
The LS1 and LS1 based truck motors are definitely prone to carboning up. You probably have some Amsoil PI lying around so you might want to run a couple of tankfuls of heavy doses of this stuff to see if it helps remove the carbon.
Mike, I have the same rig and it definetly needs to be run HARD once in awhile to keep it running smooth. I don't know if it's carbon or what, it just works. Besides it's fun [Big Grin] As for the oil, I definitly agree, thick oil doesn't help. The slap happens with thick or thin oil. I think the best approach is to use an oil that will get on the cylinder wall as soon as possible. In colder weather it could take much longer for thick oil to get there, the viscosity scale is logrithmic.
There are a lot of discussions about this on other boards. It does seem to be related to carbon buildup and use of GM carbon remover helps for a while as do others. When the carbon is built up it must make the piston tip and slap at the wall if there is any play at all. At any rate be careful, I have seen some reports of some carbon remover that starts with a B causing fuel pumps to fail when put in the gas tank. I don't like aluminum heads and got a 4.3 just for that reason. Good luck, RW
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