Clunking noise at start up.

[5pot]

Right, I've had a search through the forums and can't really find anything relevant so, here goes...

I've got a manual '05 2.0 TDI and on some mornings, when I start the car, I can hear a clunking noise. It's been around for at least a couple of months now and I suspect it's the clutch release bearing as the noise seems to go away when I depress the clutch pedal. When I apply light pressure to the pedal (without the clutch disengaging) I can feel a vibration.

When the car is warm though, the clunking seems to go away but the vibration is still there.

The clutch works as it should right now and I have noticed nothing else untoward, except a different clunk when getting on and off the throttle in a tall gear. It sounds like the gears taking up the slack/backlash when the car is changing from acceleration to overrun or perhaps slightly worn engine/gearbox mounts (Most noticeable in 6th gear, between 60kph and 80kph but does not happen all the time).

Has anyone had a similar issue? Am I right in thinking it's likely something in the clutch or does anyone have any ideas what it might be? I'm hoping it's not the clutch because I just dropped $1300 on the car last month to replace a door lock, an EGR valve and a split driveshaft boot, on top of the 90K service.

The car also has a tank of B5 biodiesel in it at the moment from a local (Laverton North, Melbourne) commercial manufacturer called BioMax.

Many thanks.

[maxrob200]

Dont think you can run Biodiesel in a Tdi. My 07 has a sticker on the fuel flap that states quite clearly - no biodiesel. maybe its the fuel. On cold starts I hear the "bag of marbles' sound and it goes away to the normal diesel-like clatter once the engine warms up

[gldgti]

lets not discuss the biodiesel here, its been discussed at length in other places and has nothing to do with the problem at hand. for the record, i've now got 8000km on 100% biodiesel on my TDI octavia, and its running wonderfully.

as for your clunking noise, i'd be checking engine/gearbox mounts first. i've had quite a lot of noisy clutches in vw's without actually having a problem apart from the noise, but not like you are describing.

if its functioning OK dont worry about it.... but do check the engine mounts. how many km on the vehicle?

[gldgti]

RWhen I apply light pressure to the pedal (without the clutch disengaging) I can feel a vibration.

When the car is warm though, the clunking seems to go away but the vibration is still there.

its quite normal to sense a small vibration with light pressureo n the clutch pedal.

also, the noise is unlikely to be caused by the release bearing, as it isnt really put together in a way as it could make a clunking noise when the clutch is engaged.

I would say its more likely to be engine mount related, or if you are unlucky, perhaps your duel mass flywheel is failing.... this type of failure has been discussed before.

[5pot]

I only included the biodiesel comment to eliminate it since the sound's been there from before the change in fuel. I'm sure it'll be fine as the company has a couple of MKV TDIs that they run on their own BD blends (up to B20). Also, I buy from the bowser that they have at the point of manufacture. But I digress.

How can I check the engine mounts? Is it a visual inspection or is there a more physical test like rocking the engine back and forth?

I'll have a search about DMF failures.

I'm not too worried about it, it's just an annoying noise.

The car's done just on 93K.

*sigh* the joys of owning cars... I have to replace the front brakes as well in the next two months.

[gldgti]

as to actually checking the engine mounts, well i'm new to the late model tdi's myself but basically if it was my octavia i'd be putting it up on stands or a hoist and visually inspecting the mounts for damage..... in my experience with my other cars trying to move the engine around maually never really gives a good indication.

The one i'd be checking first is near the back end of the subframe and attaches to the gearbox.... that'll be the main mount restraining torque forces.

[5pot]

The rearmost mount that attaches to the gearbox is the one affectionately known as the dogbone mount, yeah?

I don't think it's the DMF on its way out... The noise doesn't linger and goes away within 2 or 3 minutes of driving the car... I could be wrong though. I can't hear the clunk when free-revving the car gently when cold but that could be the engine noise drowning it out haha... I guess only a VW workshop can tell me, right?

[5pot]

Also, from reading this post:

http://www.vwwatercooled.org.au/foru...tml#post389855

what's considered "low range" revs for a diesel, to avoid overheating the flywheel. I must be doing something wrong because I like to toodle along at 60kph in sixth gear. I generally change gears at about 1700-2000 rpm. I let it rev out a bit more if I need to accelerate a bit harder though, of course. Is this bad??

[gldgti]

VW reckon that you can drive it at as low revs as you want "provided the vibration/noise is not intrusive"! This is ofcourse a bit weird, but heres what I think:

If your coasting, or just holding your speed steady on a slight down grade, I see no problem with running in gear at 1000rpm
If your on a flat road, I see no problem holding speed between say 1000-1300rpm.
If your climbing a gentle hill, I see no problem running the engine at around 1500rpm
If your climbing a reasonable hill or accelerating, I'd be keeping it above about 1800rpm. The 1.9 and 2L diesels have peak torque at about 1800rpm so they are well equipped to breath properly at these rpm and above.

My octavia has an exhaust rattle at about 1100-1250rpm......it definately depends on the temperature of the system as to how bad/noticable the rattle is.

With respect to the temperature of the flywheel thing - it will really only heat up if its slipping, so simply be gentle with the clutch but not tardy so as to take forever to engage it fully, keep the revs low and dont ride it.

[alcinodp]

I am experiencing a similar problem. I have a polo 1.6 and recently got the clutch done. The flywheel was also skimmed. Since then I hear a slight clunk on idle but noise disappears when I depress the clutch pedal. Also when in 5th gear at a decent speed, there is a noise when I let go of the accelerator. Maybe its the same overrun you mentioned which sounds like its coming from the gears itself. I am starting to believe the flywheel may actually be the problem in my case although I can't be sure in the slightest.