start up noise

[Howdey]

Hi, first time on this so we shall see what happens!Got a 3.2 V6 auto 54 plate 60,500 miles on it. Every morning on start up i hear a knocking noise from engine bay lasting for maybe 10 seconds max, then it goes. Doesnt happen any other time during day when i start, only first start of day.Cant re create the noise to show mechanics. Very worried!

[Howdey]

Hey! didnt think it would take this long.

[DeanF]

Is it a Knock or more of a rattle ?
If it only happens after an overnight stand then it is due to the oil draining back to the sump fully, Engines are generally a bit rattley 1st thing until the oil has circulated..

If there is a knocking & this is not the normal overnight stand engine noise being generated, A good competant mechanic will be able to diagnose, can you not leave it with the garage for them to hear it 1st thing ??

Cheers

Dean

[Howdey]

thanks for that, think its more of a knocking noise. someone who heard it said it sounds like a big end noise. Does a big end noise only happen when its cold? I could leave it a garage over night for them to hear first thing, just wanting to hear what others think it might be before doing that.thanks

[Big Sig]

Big ends can notmally be heard all the time I think. Although quieter than when first started.

[poves]

Mine makes some funny noises on startup also , it soon calms down though , just one of the traits of the 3.2 I think cos the engine is bang on , 37000 miles

[Howdey]

Thanks for that. its been doing this for a couple of months now, and not getting worse. Just want to put my mind at ease that its not anything big!

[DeanF]

thanks for that, think its more of a knocking noise. someone who heard it said it sounds like a big end noise. Does a big end noise only happen when its cold? I could leave it a garage over night for them to hear first thing, just wanting to hear what others think it might be before doing that.thanks

If a Big end knocks on startup you would expect it to keep knocking although it would get quieter but go deeper in sound/tone,
Big ends that rattle at startup due to shell wear or crank wear don't normally re appear until it has stood over night Etc. It's the Oil/pressure filling the gap

It's not Piston Slap is it ?? Although you normally hear of the engines that are susceptible to that.

Dean

[Howdey]

Piston slap? wouldnt know what it is! The noise is really quite loud, but after a few seconds goes completely. There is no other obvious signs. Car runs well.Forgot to mention that it had a prof gas conversion 2yrs ago, and done 40K since, but the gas system doesnt kick in until the engine has warmed up, generally within 1 mile of start up. I run the car on petrol for 50 miles or so once a month, rest of the time on lpg.

[DeanF]

Piston slap? wouldnt know what it is!

Piston slap is a Kind of GRrrrr Mixed with a Knock at the same time, Although it takes more than a few seconds to dissapear & is louder when revved !! So i would say it is not that..

I would take it to a trustworthy garage, One that is not going to Rip you off for a fault that isn't really a fault & let then diagnose, Either that or a friend of a friend Etc that Knows his Knocks from His rattles.
Listening down a screwdriver shaft with it pressed to the engine can help pinpoint, Even better with a Stethascope


But be prepared an engine sounds Terrible through one of these

Dean