Engine Rattling Noise on Cold Startup

Hello, I am currently getting a rattling noise on cold startup my 2001 996 cab for about 2 seconds and after the engine warms up the noise goes away on startup. I suspect it is failing timing chain tensioner and plan to get the 3 external timing chain tensioners replaced. However, my mechanic shop is telling me that I should replace the 2 internal Vario cam tensioners too which is a big job. There is no check engine light an as I mentioned the noise goes away when the engine warms up which makes sense being the 3 external tensioners are hydraulically actuated. What are signs of the Vario cam tensioners failing? Quoted $1,700 to replace the 3 tensioners and $8,400 for replacing all 5 tensioners. Thanks

A good way of verifying the chain tensioners is to check the cam deviations with something like Durametric. Also, when changing oil, drop your sump cover and look there as well as your filter for small plastic bits. That would serve as a good confirmation. These engines can also rattle at start up if not driven often and quite often it's the hydraulic lifters making noise until they fill with oil again. That noise should go away rather quickly or once you tap the gas pedal a bit.

Mine does the same, car is often left a week or so between weekend drives and will do it most times. If i leave it a day or two between starts then it wont, which indicates to me the hydraulic chain tensioners that can slowly lose oil over a period as they get older. They still work fine though and shouldn't cause other issues. Some people replace these if it annoys them. Starters can also cause a similar noise from dry bushes and pinions not returning. It could also be as simple as one of the exhausts heat shielding!

New tensioners, new variocam pads, new cam chains: my car still does this on cold start.

Meh....start up a mezger motor after its been sitting for a week. It sounds like a box of rocks in a tumbler.

Quotes source post: 19675670

Glad you said this because my donk is in the same boat and it rattles for the first seconds after three or four days sitting still...

$1700 is a little steep for the 3 hydraulic chain tensioners. I�m not sure what the actual parts cost is at this point, but when I did mine a few years ago, I don�t think it was much more than $4-500.00 US. That leaves $1200.00 in labor for what can�t be more than a 1 or (extremely liberally) 2 hr job� Buy yourself some really nice sockets and wrenches and throw in a quality torque wrench while you�re at it� You�ll still walk away with some change in yer pocket!

Quotes source post: 19675927

Just did this with my 996 GT3. It has not been driven for weeks. It was loud and it smoked. I need to drive it more.

Quotes source post: 19675670

I did all tensioners. No luck... Have a 2001 3.4, 36,000 mile 996.1 start up rattle for a couple seconds on every cold start. Same as its always been since i can remember. At 3.47 & 4.7 cam dev, probably actuator pads and seals might help.... Maybe the actuator internal seals are leaking oil pressure and causing the small chain to rattle...? Also have 2002 996.2. It starts quite not a rattle anywhere. Sounds like a high quality sewing machine, smooth and quite... What a difference from the 996.1 to the 996.2 on cold starts. 996.1 seems to have better throttle response. At low rpm you just touch the pedal and it responds with a rush of power. Seems more than the 996.2. But of course, all out power is in the 996.2 for sure. jmo

If you are experiencing timing chain rattle on cold start and are running 0W-40 M1 or the like, change to Driven DI-50 ( for street ) or Driven XP6 ( for track) and it will eliminate or subdue the chain rattle on start up... I have owned Sally for 2 decades and used to use M1-0w-40 European and it would rattle like crazy if it sat a few days...For the last 3-4 years I have been using several different 50 weights while doing oil pressure data collections, and the chain rattle on start is all but gone away...Every now and then I mite get a very slight rattle just for a micro-second then it goes away...Still has the original chain tensioners with 192K miles.. If you still have chain rattle after new chain pads, chains, and 50 weight oil and are going to replace the tensioners, two of them are extremely easy to eplace, probably 15 minutes,, the third is under the A/C compressor and power steering lines and will take a couple of hours at least.. You can stay with a 40 weight if you drive around like a Grandmaw, otherwise switch to a 50 weight. Not only will it stop or reduce the chain rattle to min, it will greatly stabilize the oil pressure during high G, high temp corners...

I just bought a 1997 Boxster with 56,000 miles on it. When it sits for a few days without a startup it will rattle for a second and then quit and sounds puuurfect. I just did an oil change and the oil was fantastic with no plastic or metal flakes. Using 5W30 Mobile 1 European formula that was recommended and may go to a heavier weight next time around and see if that clears it up. With those low miles I would not suspect any internal issues yet.

1 or more chain tensioners may be bad. They leak down and the chains rattle until pressure is restored.

Get a reading on the cam deviation and if it's out os spec get them changed. If your 4 or greater switch them out. I just had mine done on my 01 and it costed me $6800.....but while they were in there I had them do a bunch of other things as well. Highly recommend getting a reading done.