1997 vortec 5.7 start up

[Anthony Ray]

I have a 97 tahoe with a 5.7 vortec and when I start it up in cold weather it sounds as if the piston is slapping the valve or just piston slap in the cylinder wall. Has anyone ever experience this?

 

[df2x4]

My '97 K1500 Suburban with the 5.7L has a slight tapping/clicking sound on the first start of a cold day (below 40 degrees or so) that goes away within a minute or two of starting the engine. It's done this for several years now. My mechanic suggested an engine cleaner (from BG IIRC) that you run in the oil for a short interval prior to a change, I tried it and unfortunately it didn't help much if at all. I'm planning on sending an oil sample to Blackstone Labs again next time I get it changed, but I sent one in a few years ago and it checked out fine. The noise hasn't gotten any worse so I've kind of neglected it.

 

[kennythewelder]

My 97, 5.7L does the same thing, but I do have a tune. So today, I reprogramed it from the premium fuel setting, to the mid level setting. I will see what happens in the morning. It will be around 40° F tonight. I have also found that it is using oil, but doesn't smoke at all, and only has a very small leak from the rear main seal. So at 257,000 plus miles, am I burning the oil, IDK, I guess I need to pull the plugs and see what they look like. I have some vacation time around Christmas, so maybe then. Mean while, my truck runs grate. Tht tells me, it's nothing major.

 

[Nad_Yvalhosert]

40°! That's a heat wave to us in New Yuck.

Sad to say, my 214k mile '00 Denali 5.7 has a little slap first thing in the 22° we had yesterday morning.

I'm running 10/40 oil during the warm months, its due for a LOF in about 900. That's when I'll drop to 5/30.
OP, what viscosity are you running?

 

[kennythewelder]

10-40 Valvoline high millage. The reprogram of the ECM did help, but the slap is still there. Funny thing about the reflash, is that the truck seems to run better on the mid level gas setting that it did on the premium setting. I'm running premium in the truck, and plan to keep doing so.

 

[Erin]

Not sure if this is yall's issue, but I had a lifter do that on cold mornings.

 

[kennythewelder]

Not sure if this is yall's issue, but I had a lifter do that on cold mornings.

Mine is not a lifter. It's more of a piston slap, rod, main bearing noise. It's not a tic, more of a knock coming from the bottom end, not the top of the engine. It goes away in maybe 1 minute or so, and only does it when it's cold out side (40 ish, or colder) and only after sitting over night or longer.

 

[wirlybird]

My '97 Tahoe 5.7V does this also and has since about 100k miles, 322,000 on it now.
It sounds like a cross between valve lifter tick and a faint knock. Mostly goes away after it warms up and is much more prevalent in the winter/colder months.
My research found that it could be piston slap due to short skirt pistons used. I found several threads on this years back. After digging into it I found it seems to be quite common.
On mine there is no indication of a more serious problem and especially since it has gone about 200,000 miles more since this started.

 

[Erik the Awful]

Thicker oil isn't going to stop piston slap. The solution is to get larger pistons, measure the pistons, and machine the bores to fit.

These motors weren't blueprinted from the factory the same way many contemporary engines were. Piston slap is pretty common. These trucks were much newer when I was a Nissan technician in the late '90s, and we always had a few on the used car lot. It was pretty common to get some piston slap on cold mornings. By contrast, Nissan was replacing engines that developted slap because their piston supplier had mis-marked a crapload of pistons and they were something like .0005" off.

It's not terminal, just annoying. I'd run it until it doesn't run.

 

[PlayingWithTBI]

Years ago (in 78 IIRC) I had a 70 Buick Skylark with a 350. I was told it had piston slap until the torque converter finally went out. Replaced it and drove the thing another 2 years before getting rid of it.