innovator

Hello gentlemen.

I posted this on the 996 forum, but then realized that there was a 996 turbo forum. I got some great replies but I'm still looking for some more input, as I still am uncertain if the noise is normal. I understand that the turbo does not have common IMS issues, but I am concerned something may not be right.

I just picked up a 2002 996tt with 10,000 miles on it. I traded in my 2003 Audi RS6. All seems well, except that after warmed up, I hear a rattle coming from underneath the engine. I am an Audi tech, and I hear engine noises all the time, but this has me a little nervous. I know these engines aren't silent, but it seems a little loud to be normal? I may have been a little to over-zealous when I picked up the car, and overlooked it...

I read about the IMS shaft issues, and the only way I can describe this noise is like a rat,rat,rat,rat.... Seems to get worse when the engine is hot, but diminishes when the engine is reved over 1000 rpm. Depressing the clutch makes no difference.

Thank-you Rick

jcb-memphis

Lightweight flywheel perhaps? <- if clutch pedal changes the noise....

If not, IMS. Likely normal. I have just grown to accept the noise.

Cannot hear mine over the exhaust and lwfw. Sorry, I misread your post....I am not off my rocker quite yet...not likely lwfw....just the normal stuff.

Enjoy your new car. T2 has something like 200 or 300k on his with 5k mile 0w-40 changes....so these cars can take it.. .he tracks his car. I use 5w50 and feel it and the dreaded turbo diesel 5w-40 M1 oils are fine. Have heard good things about elf too.

We love pictures too, btw. Welcome!


JB

innovator

I don't know if the previous owner changed the flywheel, but the trans bolts seem untouched. Other than the spoilers, the car appears stock. Clutch has no effect . When the ac compressor cycles it stops momentarily. It goes away when revved over 1100 rpm Only 10k on the car. Runs perfectly otherwise.

NewYorkBuck

I have that rattle - from 875-1000 rpm. Goes away above and below. Always been there. Not going to worry about it as the car runs great otherwise.

doubleurx

Normal. I am surprised at the first responses. This is a known sound with the TT. If it goes away like you say, then it is nothing to worry about. If it were a flywheel / clutch issue, it would change when you depress the pedal.

innovator

Yes I agree. It is definitely not the clutch or input shaft bearing. I thought it might me the gears rattling on the shafts in the trans at first , but the noise is clearly emanating from the front of the engine.

Guybrush Wilkinson

Can somebody explain what causes the rattle? What parts are moving against each other?

I read somewhere that changing thicker oil (5W-50 instead of 0W-40) helps but there allways is a rattle when the engine is hot. Oil pressure related thing?

MechanicalEng

This has been discussed a lot, the IMS in these cars is loud, do a search here an on youtube for 996TT IMS noise and you will find a ton of info

Kevinmacd

Gear and chain noise from the IMS. They all rattle. BTW some on here state that using 5w-40 M1 Delvac diesel oil reduces the noise a bit. Has been discussed many times on this board. What you have explained is the normal situation. Once revved up it dissappears says you have nothing to worry about.

jbossolo

^What he said. I switched to Delvac, as per Kevin's rec.

Macster

Assuming the 'rattle' is coming from the IMS and its gear drive the noise is not an oil pressure issue, since oil pressure per se doesn't exist at the gear teeth interface. (The oil's high temp sheer resistance might be a factor though.)

This assumes of course the rattle is not due to excessive bearing clearances at the crankshaft or IMS bearings too, which while possible is a very very rare problem.

The rattle basically arises because the engine, the crankshaft, at low speed (at any speed) has normal variations in its rotational speed. Each time a power stroke occurs the engine crankshaft speeds up a noticable amount. (It is this momentary increase in speed or lack of it that the DME relies upon to detect misfires.)

Because the crankshaft's rotational speed varies the gear teeth of the crank speed up and slow down in time with the crank's change in speed.

Since the crankshaft and IMS gear wheels, the gear teeth on the gear wheels, have some clearance this clearance results in a rattle as the crankshaft experiences short term speed ups and slow downs during idle and low speed running.

Another contributing factor is the resistance the IMS has to being turned varies because of the periodic variability of the opening of the intake/exhaust valves.

Fresh oil or even a heavier oil might reduce this noise, though I have already voiced my strong objections to using something like a diesel engine oil in the hopes of quelling this normal noise, so I could never go along with that recommendation.

There is a Mobil 1 5w-50 oil (not a typo for 15w-50 oil I always like to add which is just about as bad as diesel engine oil imho) that is an approved oil.

I run this in my 03 Turbo. In fact I just bought three 6 quart cases at a local Mobil oil distributor for $142.11 or $7.90/quart cause the Turbo's due for another oil/filter service this week. (And the Boxster too.)

Sincerely,

Macster.

"02996ttx50

i have been adding the 5/50 M1 to a typical 0/40 oil change and it significantly quiets the noise we all seem to have. the sound is awful, and though i know my car at idle is well within a "normal "range, who can quite get used to it?

a funny side note is that on my last ttx50, i never heard the noise at all ( 20 to 50 k miles ) until i asked that the oil in the turbo's be drained as part of an oil change which many techs either neglect, or choose not to do. i immediately noticed the noise after running the car and the dealer tech said that i was now hearing the turbos "cavitate". i'm not sure i believed him, and thought that only submarines "cavitated". who knew?

Kevinmacd

Not the turbos. open the engine lid and stick you head in you will hear it right at the where the IMS gears and chains are.

MK19

This is normal noise from the straight cut gears between the Crank and the intermediate shaft. It was there all along on the 993's and 993TT.........but with air cooling it was muffled. Now with H2O cooling, we can hear it.

When it's off idle the gears load up a bit and dampen the rattle between gear teeth.

Normal, annoying and not fixable as there is no adjustment between the gear centers. The best you could ever do is sellect a tighter set of gears from among the many. I under stand, but have now real confirmation that later 996TT's got tighter toleranced gears that can be slightly less noisey......at least that's what the Porsche field rep told me.

MK19

Macster

Well, I can't hear the noise but if it is normal (and I strongly suspect it is 'normal') then I think you may be fixating on this a bit much.

Let me point out this engine has some competition in its heritage and is able to put out 420hp from 3.6l. (My 06 GTO with its 6.0l V8 only put out 400hp!)

What this means, talking about the Turbo engine now, is that engine is a pretty tuned engine out the box. IOWs, it is a bit more raw than the engine found in the more common sedans and coupes running about.

Also, of course the engine has a gear drive between the crankshaft and the IMS. The IMS in turn has quite a bit of chain that it uses to spin the 2 cams under each camshaft cover for a total of 4 cams, and a lot of intake and exhaust piping crammed in a pretty tight space right behind the passenger cabin.

Then there's the VarioCam Plus which provides for variable intake timing but variable (high or low) intake valve lift. While this hardware is very robust (but proper oiling is critical to its continued good health) but at idle and especially at cold idle I suspect some of the engine noise arises from this hardware.

Furthermore, the Turbo engine compartment is a bit more open than your usual front engine coupe/sedan, most of these have 'tons' of sound deadening under the front hood and some even have special engine covers which are there to minimize the engine noise.

To add insult to injury (so to speak) the Turbo has those intercooler air intakes which can direct some engine compartment noise up to where a driver with the window down or the door open even would I'm sure hear the noise better.

We each of course react differently, are more or less sensitive to noises, but don't let a perfectly good high performance based engine that makes a bit of mechanical noise spoil for you what is a very very fine automobile.

Sincerely,

Macster.