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Cold start knock

M96

Member
Joined
15 Oct 2017
Messages
10
Evening,

Firstly, thanks to the advice on my CEL query last week - a good clean of the MAF, and all clear (so far at least!).

Now on to my current woe...

I've got a knocking sound when engine started from cold. If started once there's a bit of heat in it / been driven for >2 miles there is no abnormal sound.

I know it's virtually impossible to diagnose without a video, but I can't seem to upload one as it stands

It's not got any worse as far as I can tell, and have now completed a further 2000 miles.

It hasn't used a drop of oil in the 2k miles, and coupled with being a 3.4, pretty sure it's not bore scoring..

Seems too regular for ims issues; thought this was more of an irregular rattle and would have been catastrophic by now I guess

Seems too low down, and not enough of a high frequency 'tick" for a sticky lifter.

It doesn't change with clutch actuation

Other things running through my head as possibilities it might be...

Water pump / other auxiliary bearing / unit (how common this stuff gives issues?)
Big / Little End wear (hope not!)
Some kind of chain rattle / guide wear (though seems too much of a 'knock" for this)

You cannot hear anything once warm (which I guess would be more of a concern), but i'm worried there is something lurking that needs some preventative maintenance, not to mention the noise grates on first start up each day!

Any thoughts would be much appreciated....?
 
Hi M96,
As you say, without a video it's hard to tell but these engines are known for emitting various sounds at idle on cold start.

A few main ones are -

A grating/rattling for a split second on cold start up which is cam chains flapping about until the oil fed tensioners pressurise and tensions them. Some cars do this some don't.

A consistently timed ticking that may come and go. More of a clicky tick than a solid knock. This could be a sticky tapper/lifter.
Not much you can do apart from regular oil changes.

The third which I'm guessing yours maybe is only on cold starts as you've said.
The car starts with no knocking for ten or twenty seconds. Then faintly it comes on over a few seconds until you can hear it clearly then it fades in and out until it goes off completely after about 30 seconds to a minute.

Mine does this and it sounds like piston slap but I don't think it is as my mate's Hartech rebuilt car does worse than mine and it only has 20k on it.
I just ignore it as nobody can say for sure what this is.

I'm sure Hartech wrote a big piece on ticking and knocking noises a few years ago. A lot of them are harmless. Maybe search their site.

Of course you could be talking about something totally different in which case ignore me. :wink:
Maybe just ask your mechanic to have a listen next time it's in.

:thumb:
 
Take an oil sample and send it off to an oil analysis company. They will tell you what is in there and if you see a very high copper count that will tell you that one of your bearings is being destroyed. I would do this sooner rather than later because if it's a big end bearing you will be into thousands if the crank is scrap, and the longer you run it, the more likely this will happen.
 
Hi M96,

As Marky911 said, i'm his mate who's engine has the slight knocking on start up.

My car has had a Hartech rebuild abut 25k miles ago back in 2008. Since I've owned it, after start up about 5-10 seconds in it develops a faint knocking then sometimes gets a little louder then goes faint again until it disappears all together once there is a little heat in the engine.

I did search this site about the problem and remember coming across a post from Baz at Hartech saying that these engines can knock from time to time whether they've had a rebuild or not. This put my mind at ease a little.

I have had my car coming up 5 years and not had any issue other than the annoying knock at start up. There are times that mine doesn't even knock at all so god know what is actually causing it.

My mechanic always checks the oil filter for any signs of metal fragments and there has never been anything yet, so he just puts it down to a bit piston slap. (Best guess anyway)

I'm obviously not saying that your issue is the same as mine, so always best to get it checked out by someone that knows what their talking about.

Hopefully its nothing serious.....

Good Luck

:thumb:
 
Thanks for the feedback all.

Marky911 and cobrars; that sounds very much like the same symptoms, but I think i'll get the oil sent away for analysis to (hopefully!) give piece of mind nothing more sinister...

Thanks again!
 

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