Hi, I own a 2000 Corvette and on a cold start up it makes a strange noise. I’m not sure if it is a valve lifter or maybe piston slap? It gets quiet after a few minutes of running. Any suggestions?
You are right for not being sure whether it’s valve lifters or piston slap, because they are both valid diagnoses that are impossible to verify without an engine teardown. As much as I love GM’s GEN-III and newer pushrod engines, these quality niggles do drive me nuts ...
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Are there particular years of the displacement on demand that are worse than others? I'm not in the market now, but I could see replacing my 2002 Yukon XL (5.3, non-DoD) with a newer model in a few years.
@Sajeev, I've heard plenty of griping about DoD-caused failures, too, but how common is it really? I mean, GM has sold millions of these trucks. Any TSBs? I get wanting to avoid the DoD motors if you're looking for cores to build for hotrodding because it's just added complexity you have to deal with, same as with variable valve or cam timing. Not saying it doesn't happen, but maybe it's just the circles I run in, a lot of griping I hear is from old-timers who seem to distrust any new technology. On the other hand, I don't hang out in LS forums.
There was an issue with piston slap in the early to mid 2000s. I remember reading an article in Hot Rod magazine about it. This is a just an arm chair diagnosis so take it for what it's worth. If it was a collapsed lifter, then it would tick. Although, a hydraulic lifter will bleed down a little with time. If a car sits for an extended period of time with hydraulic lifters whether roller of flat tappet, it will tick until the oil pressure pumps it up. That being said, taking into account the service bulletins for the early LS1 engines, as well as the articles covering them, I would be willing to bet it's cold engine piston slap. Don't take that as the gospel.
Basically, the first engines had tolerances that were too tight. In an effort to combat premature wear and warranty claims, G.M. loosened the tolerances, maybe just a little too much which resulted in cold engine piston slap, and then service/warranty claims about a knocking engine when cold started filing in.
To be honest about the whole thing, I wouldn't trust either. Too tight a tolerance, and you get premature wear and an early replacement/rebuild. Too loose and you get premature wear, and early replacement/rebuild, or if left unaddressed and that piston is hammering back and forth harshly, the possibility of a broken piston that will eat the rest of your engine, or a gouged/damaged cylinder. Neither is good.
That being said, I have seen the slap happy "looser" engines last a pretty long time. Take a broom handle and put it against your rocker covers. If it is a valve train issue it will be heard through the broom handle when you put your ear up to it. You could also use an automotive stethoscope and do the same thing if you really want to find out whether or not it is in the cylinder, or in the valve train.
I wish I had the data to answer your question @ValuedCommenter, but it's not just "old timers" having the problem. I would buy any 5.3 DoD truck with the full knowledge that it might need a new engine because of this flaw plus owner neglect, and be prepaired for a failure. Luckily replacement engines are cheap, a shop can go thru a used one, delete DoD and you'll have a great vehicle afterwards.
Maybe you'll get lucky and you can just DoD delete whatever you buy and it will be fine.
My bought new in 1999 2000 Silverado had the somewhat unusual 4.8 V8. Virtually from day one, it experienced lifter or piston slap noise on start up. The noise would continue anywhere from 5 to 25 seconds or so, depending on the ambient temperature. In 17 years of ownership I put over 230,000 miles on the vehicle. Replaced hubs, a/c compressors, and, at 210,000 miles a transmission. The engine never experienced any significant repair, and consumed zero oil between regular 3,000 mile oil change intervals. A great motor.