The dreaded pistion slap?

I just turned 210,000 miles on my 2003 Silverado, and I have started to notice what sounds like piston slap when at warm idle. When I start the truck in the morning, it sounds fine. But once the engine warms up, then I hear the noise. I'll rev the engine up to 2000-3000 rpms for a couple seconds, then let it idle, and the noise is gone. But 10-20 seconds later, it slowly comes back. I do not hear the noise at all when driving the truck. I tried SeaFoaming the engine through the throttle body and the brake booster vacuum line thinking it was carbon build up, but this did not fix the issue. However I may have eradicated the entire mosquito population!! :runaround:

I've read that piston slap on these trucks only happens during a cold start. This is not the case with my truck. But am I still hearing piston slap?

Any help would be great. Thanks!

2003 Silverado W/T 4.8L V8

Piston slap occurs almost from day one, hot knocking could be anything in the engine at that mileage,have someone sharp with engines listen to it.

I just turned 210,000 miles on my 2003 Silverado, and I have started to notice what sounds like piston slap when at warm idle. When I start the truck in the morning, it sounds fine. But once the engine warms up, then I hear the noise. I'll rev the engine up to 2000-3000 rpms for a couple seconds, then let it idle, and the noise is gone. But 10-20 seconds later, it slowly comes back. I do not hear the noise at all when driving the truck. I tried SeaFoaming the engine through the throttle body and the brake booster vacuum line thinking it was carbon build up, but this did not fix the issue. However I may have eradicated the entire mosquito population!! :runaround:

I've read that piston slap on these trucks only happens during a cold start. This is not the case with my truck. But am I still hearing piston slap?

Any help would be great. Thanks!

2003 Silverado W/T 4.8L V8
Watch and determine the oil pressure, I think you hear noise when the pressure drops. This is probably a good time to upgrade if the oil pressure is low.

with what you have is most likely a oil problem with the piston having carbon in the rod.

put 6 OZ of marvel mystery oil in the crankcase and run a few hundred miles to see if the sound quiets down. I do not use sea foam because it is a solvent. also using these solvents as you did the oil need be changed after you use these products.

marvel mystery oil MMO is an oil that slowly cleans and removes carbon deposits. I would also use this in the fuel 1 OZ per 10 gallons or 3OZ in a fill up.

MMO I have had great success. the 2000 I had when new had this only cold piston sound now with the MOBIL1 that is GM dexos spec no slap even when we had the 0 deg f here.

with what you have is most likely a oil problem with the piston having carbon in the rod.

put 6 OZ of marvel mystery oil in the crankcase and run a few hundred miles to see if the sound quiets down. I do not use sea foam because it is a solvent. also using these solvents as you did the oil need be changed after you use these products.

marvel mystery oil MMO is an oil that slowly cleans and removes carbon deposits. I would also use this in the fuel 1 OZ per 10 gallons or 3OZ in a fill up.

MMO I have had great success. the 2000 I had when new had this only cold piston sound now with the MOBIL1 that is GM dexos spec no slap even when we had the 0 deg f here.

Thank you for your quick responses everyone.

I have been monitoring the oil pressure and I haven't had any problems with that. When warm and at idle, the oil pressure is hovering just shy of 40 psi. At WOT, it almost reaches 80 psi. Cruising, it is problems somewhere around 50 psi. So I don't think oil pressure is the problem.

When I used the seafoam, I did change the oil around 200-300 miles after its use since I did pour some into the crankcase. I had my mechanic take a listen to it and he instructed me to substitute a quart of oil for a quart of Lucas Oil Stabilizer at my next oil change. I changed my oil 2 weeks ago and have put 1,000 miles on it since. It quieted the noise down somewhat, but it is still noticeable.

I have about 3/4 of a tank of fuel in it now so I'll add a bit of MMO to the tank today.

Should I wait till my next oil change to add the MMO to my crankcase? I usually change my oil every month due to the amount of mileage I put on the truck. Also, is this something I should do routinely? I love this truck and it has never failed me in any way. This is the first time I have had an issue like this.

Thanks!

Thank you for your quick responses everyone.

I have been monitoring the oil pressure and I haven't had any problems with that. When warm and at idle, the oil pressure is hovering just shy of 40 psi. At WOT, it almost reaches 80 psi. Cruising, it is problems somewhere around 50 psi. So I don't think oil pressure is the problem.

When I used the seafoam, I did change the oil around 200-300 miles after its use since I did pour some into the crankcase. I had my mechanic take a listen to it and he instructed me to substitute a quart of oil for a quart of Lucas Oil Stabilizer at my next oil change. I changed my oil 2 weeks ago and have put 1,000 miles on it since. It quieted the noise down somewhat, but it is still noticeable.

I have about 3/4 of a tank of fuel in it now so I'll add a bit of MMO to the tank today.

Should I wait till my next oil change to add the MMO to my crankcase? I usually change my oil every month due to the amount of mileage I put on the truck. Also, is this something I should do routinely? I love this truck and it has never failed me in any way. This is the first time I have had an issue like this.

Thanks!

put the 6 OZ of the MMO in the crankcase now . it mixes well with the oil.

I just got some at walmart $4.65 a qt, when I used non synthetic this was used at every oil change. I got 380,000 out of my 1983. when I sold it it still ran perfect and never failed emission test. just remember more is not better only use the amount I stated....

put the 6 OZ of the MMO in the crankcase now . it mixes well with the oil.

I just got some at walmart $4.65 a qt, when I used non synthetic this was used at every oil change. I got 380,000 out of my 1983. when I sold it it still ran perfect and never failed emission test. just remember more is not better only use the amount I stated....

Ok I went out and bought some and put an ounce in my gas tank and 6 ounces in my crankcase. I then took it out for a 15 mile ride through normal highway driving, and stop and go driving. I just drove it like I normally do.

When I got back, I noticed a world of a difference. The tap is still there, but it is already much quieter than before. I know it isn't going to be perfect with the high mileage that is has, but it has already made a world of a difference.

Thank you so much for your input. I really appreciate it! I try my best to be ginger with my truck and stay on top of the maintenance.

Ok I went out and bought some and put an ounce in my gas tank and 6 ounces in my crankcase. I then took it out for a 15 mile ride through normal highway driving, and stop and go driving. I just drove it like I normally do.

When I got back, I noticed a world of a difference. The tap is still there, but it is already much quieter than before. I know it isn't going to be perfect with the high mileage that is has, but it has already made a world of a difference.

Thank you so much for your input. I really appreciate it! I try my best to be ginger with my truck and stay on top of the maintenance.

sounds good . you had / have carbon issues. continue to add the MMO when fueling. watch for the engine oil to turn black or very dark. this is the MMO breaking up the carbon deposits. change oil /filter when it gets too dark.

with continued use of the MMO at each oil change the engine will gradually get cleaner and quieter if it is the carbon issue . good luck ...