00Coupe

Hello

I have a 02 996TT and if the car sits for an extended time I get a bit of timing chain rattle for a few seconds at cold startup..

If I pull the fuel pump fuse prior and crank it over for 5-6 sec, there is no chain rattle..

This sounds to me like the car doesnt hold oil pressure to timing chain tensioners.. Has anyone else had this sort of concern?

fpb111

Just about all 996 turbos do this.

Macster

Be sure the oil doesn't have too many miles on it. As m Turbo approaches its 5K mile oil/filter service interval it is a bit noisier at cold start.

The noise is normal. The tensioners and lifters bleed down some.

I'm not a fan of cranking the engine with the fuel pump fuse pulled. There can be some fuel pressure and the injectors are still triggered. Even with no positive pressure fuel will dribble out and what does washes away or thins at least the little oil that is at the cylinder/ring/piston interface.

Another problem is the starter spins the engine very slowly on the order to something under 150 rpms. While this might be fast enough to provide some oil to the tensioners it probably doesn't supply sufficient oil to all plain and sliding bearing surfaces.

Plain bearings are hydrodynamic and this type of bearing requires rotational speed and some load and oil pressure to generate the oil film "wedge" to prevent metal to metal contact.

The slow spinning of the engine doesn't generate much if any real oil pressure and the spinning is not fast enough to build up much of an oil wedge. The slow spinning instead just depletes the residual oil that is present, works to squeeze out. It had two paths to leave the bearing with insufficient oil pressure and flow. Out the normal way and to flow back into the oil groove and the oil groove oil supply holes.

Up "top" the cam lobes and lifter faces are splashed lubed by oil that comes from around the lifter bucket. Slow spinning doesn't get the oil up there and any residual oil is kind of wiped away.

Porsche if it were of any benefit could certainly add some delay after the engine starts rotating under starter power before turning on the injectors and triggering spark.

But instead it -- along with every other automaker I'm aware of -- has the engine firing right up with the DME causing the RPMs to shoot up to near 2K before letting engine RPMs drop to just over 1K. This is to create the initial oil film wedge at the plain rotating bearings and at the same time get the oil pump gears spinning to supply oil pressure to then sustain the oil film wedge and at the same time supply sufficient oil to ensure the furtherest reaches of the engine, the cam lobes and lfter bucket faces, get oil as soon as they possibly can.

At slow cranking speed oil appearing at these locations can be delayed as the lifter buckets may need recharging with oil as they have bled down from the engine being off, assuming oil even makes up that far in the oiling system at the slow cranking speed. The main oil galleys act as an internal oil leak of sorts taking alot of the slow spinning oil pump's output so little to no oil flows to the lifter buckets. And the oil feed passages to the lifter buckets and cam bearings like the main oil galley passages initially are internal oil leaks taking some quantity of oil to fill up and force oil to flow to the cam bearings and the lifter bucket oil feed holes.

My Porsche techs advise me that for Porsches that see infrequent use that the use of Swepco 502 Oil Improver can help reduce cold engine clatter. As my cars see frequent use I never noticed any reduction in noise at engine start so I no longer use this stuff.

But maybe in the case of your car there will be some benefit.

Kevin

I pull the fuel pump fuse on my cars when they sit more than 3 to 4 weeks.

As a small recommendation.. When you replace your oil filter, inspect and replace the small oring. This will keep oil prime longer between engine starts. It will also reduce engine oil pressure bounce.

As the engine ages hydraulic lifter leak down does occur.

BTW, since this is a flat 6.. The rings will wipe the skirts but as the piston travels back to top dead center oil flows across the cylinders since/because we have oil/piston squirters.. The cranking of the engine supplies oil pressure to the lifters and relubes the piston skirts and cylinders.. So crank away. A little fuel dilution will get burn up and evaporated when the engine gets up to temp.

"02996ttx50

i get rattle and screech at startup and the sound is enough to make me wince. it used to occur with greater frequency ( and happens less when driven daily ) when i ran 0/40 and has been mitigated somewhat by running 5/50. although *normal* it's disconcerting nonetheless. i *probably should* pull the fuse but haven't bothered.

Kevinmacd

With 40k on the clock, if the car sits a few weeks I get lifter noise for about a sec. I equate this to oil bleed off of the lifters, never chain rattle. If used 1x a week I dont get any lifter noise.