kksi

Hi:

My 94z LT-1 has a mild to moderate banging at start up in cold weather but after 15 seconds or so it disappears. Im not a mechanic but it doesnt sound like a valve tap, something deeper. Is this something to worry about?

Like I said after about 15 seconds or so the banging stops and drives and sounds great.

Thanks for your input.

87Aerocoupe

What's your oil pressure look like, is it low, if so could be a bearing going bad?

kksi

It seems fine during normal driving conditions. When Idling it approaches the red line but Im thinking it has always done this and then when accelerating it goes back to normal.

bw_hunter

It sounds like a bad bearing. Yes, it's something to worry about. If it's a heavy sounding knock...like a big hammer hitting an anvil, it's probably the mains.

kksi

Its more of a mild to moderate sound. Is there a way to diagnose it or am I at the mercy of the garage and their diagnosis?

lt1-xjs

If it does it first thing in the morning and then goes away, doesn't do it any more till the next day, It's likely piston slap and yes it is common.

Injuneer

What viscosity oil are you using? What is the ambient temperature when this happens?

grabbem88

Mine's been doing that since 170k or so and I thought was from oblong cast pistons but I never hear after 10 minutes of running

I've been running on borrowed time for a looooong time lol

shoebox

Post some audio of the noise. Near impossible to diagnose a noise without being able to hear it.

maybe2fast

audio or video is required

GaryDoug

Badly worn crankshaft bearings will get noisier with hotter engine and oil. i.e. Quietest when cold, loudest when hot (especially when accelerating). Not likely in your case.

Chimera96

a "guess" based on Op's description is piston slap. some experience this and have for several years

take a close look at oil and cut open filter ...if "sparkles"...than bearings

Injuneer

Somehow, use of the word "banging" (even if "mild" or "moderate") sounds a lot worse than the typical gentle thud of piston slap. Could be oil that's too thick to circulate in extreme cold. But we still don't know what oil he is using, and whether it's particularly cold when this happens.

kksi

I agree that banging is too harsh a word. A piston slap seems correct and more appropriate. I dont change my own oil and regularly have it done at a service station. I hope and trust they use the recommended oil. The "slap" only happens on very cold days and again only lasts 10 20 seconds or so. Then it disappears. My intent on this thread was to see if this is an indicator of long term problems and if there is anything I can do to prevent any further damage. With 140k miles, should I consider a synthetic oil?

Injuneer

Piston slap of the type you describe is very common on the LT1 (and the LS1 as well). Does not do any permanent damage. Make sure they are using 5W-30 in cold weather. Makes no matter whether its synthetic or not.