piston slap or rod knocking ????????

I have a 1999 Suburban 4x4 with a 5.7 engine and 150,000 miles that I have owned sense new. I took it to Pro-Gear in San Diego to have the rear end fixed. They put it in the air and ran it to find the bearing noise problem when they and I heard a noise coming from the lower part of the engine. It is a tapping or knocking sound. The faster the engine went the faster the tapping was. I took it right home and change the oil and filter (mobile 10-30) and added two quarts Lucas additive to the oil. The magnet oil plug had very small black metal on it. I normal change the oil every 4,000 miles or so. I used the oil additives to prolong the engine life over the weekend. Could this knock or tapping be piston slap? Is it reasonable to think about dropping the pan and replacing the rod bearing if that is what it is or with the knocking is the crank gone too? I cannot hear the knocking with the engine running and hood open from the topside. Can the pan be dropped with out lifting the engine or dropping the 4x4 axle out? Any idea how long it will run this way? I am think about a crate engine replacement when this one blows. Thanks for any ideas on the engine. Dave

Hope this helps,if the drain plug had a fuzzy look,that's normal. If it was chips,that's a problem. If your not losing oil pressure bearings and crank should be ok. I've heard oil pumps make noise(from the bottom only).Why 10-30, with 150,000 i'd give it some cushion and use 20-50. Heavy additives tend to settle on the bottom. My opinion,for what its worth...GOOD LUCK!

Thanks yknot
I will use 20-50. I did not think of it. Would i get new metal with a rod bearing coming apart or are the bearing not steel but some other type of metal that would not stick to a magnet? Dave

Sure will Dave. They're usually tri-metal. A soft babbit like towards the crank,a bronze type center and the steel backing. You'll see gray & gold color specks in the oil that won't stick to the magnet and the steel that will. By this time the noise would be louder. Either a chirp(squeal) or knock and oil pressure will drop. 4,000 mi. between oil & filter change should keep that big block alive. I just sold a 1990 big block burb with 182,00 mi.(original motor). The new owner is still running it.

My 97 Burb has had piston slap from day one and the dealer told me unless it blows they can't do anything about it . Now with 119K miles the noise is still the same, no better, no worse. I do use only Mobil1 5w30 as the manual reccomends, from what other real life technicians have said, you should stay with the thinner oil to insure librication gets to where it needs to.

There is a thread about oil and towing, try to find it and see what those guys said.

in most of my experiences bearing material ends up in the oil pump pick up screen not on the plug. you can take a sample of the oil and get it analyzed if need be. or cut apart the oil filter

yes i agree with gregory914 5w30 is the best, most damage is done at cold starts the 5w gets to the moving parts quicker cutting down the metal to metal wear, 20w50 is for racing