Questions About Start-Up Rattle

[Seadweller]

Hi gang!

I know this has been discussed ad nauseum, but I have some questions related to this, some of which I can't find answers to. I of course have the notorious start-up rattle, which sounds like the motor is coming apart for a second or two. It's not a comforting sound. My '98 has around 38K miles on the clock, and the IMS has been done. One thing to mention is that I can go 2-3 months at a time without starting/driving the car, which I'm sure exacerbates the issue. On to my questions:

1. I've read quite a number of instances where folks have installed the updated tensioners, only to find that the rattle persisted. What I haven't found is a root cause as to why the new tensioners did not correct the problem.

2. Related to #1, if the tensioners didn't fix the problem, then folks seem to point to the ramps. Could an engine with 38K miles have that much ramp wear to cause the rattle?

3. Thinking of ways to get around this, is there any harm in pulling the fuel pump fuse and turning the engine over for a few seconds to build pressure in the tensioners?

I'm getting ready to bring the car in for a service, and am wondering if I should go ahead and have at least the bottom 2 tensioners replaced as a precaution. I'm just trying to stay ahead of the curve, but I'm not ready to address the guides, as that's quite an endeavor.

Thanks!

[JFP in PA]

Originally Posted by Seadweller

Hi gang!

I know this has been discussed ad nauseum, but I have some questions related to this, some of which I can't find answers to. I of course have the notorious start-up rattle, which sounds like the motor is coming apart for a second or two. It's not a comforting sound. My '98 has around 38K miles on the clock, and the IMS has been done. One thing to mention is that I can go 2-3 months at a time without starting/driving the car, which I'm sure exacerbates the issue. On to my questions:

1. I've read quite a number of instances where folks have installed the updated tensioners, only to find that the rattle persisted. What I haven't found is a root cause as to why the new tensioners did not correct the problem.

2. Related to #1, if the tensioners didn't fix the problem, then folks seem to point to the ramps. Could an engine with 38K miles have that much ramp wear to cause the rattle?

3. Thinking of ways to get around this, is there any harm in pulling the fuel pump fuse and turning the engine over for a few seconds to build pressure in the tensioners?

I'm getting ready to bring the car in for a service, and am wondering if I should go ahead and have at least the bottom 2 tensioners replaced as a precaution. I'm just trying to stay ahead of the curve, but I'm not ready to address the guides, as that's quite an endeavor.

Thanks!

1. Because the chain ramps are worn.
2. Yes.
3. Won't hurt, but will not help if the ramps are worn.

Easiest way to find out is check your cam deviation values, if they are high, the ramps are worn.

[Homeoboxter]

Another possibility is that the variocam actuator loses oil pressure over time because of the worn/rigid O-rings inside. It takes quite a few revolutions of the crank to re-pressurize them. Does it rattle every time you turn on he engine or only when you don`t use it for long? I think for a `98 a couple second rattling is not the end of the world after a 2-3 month resting.

[pilot4fn]

As a winter project couple a months ago, I did replace cam- and IMS-to-cam chainramps as well as tensioners, now the start up rattle has disappeared. Well worth the effort.

[Seadweller]

Originally Posted by Homeoboxter

Another possibility is that the variocam actuator loses oil pressure over time because of the worn/rigid O-rings inside. It takes quite a few revolutions of the crank to re-pressurize them. Does it rattle every time you turn on he engine or only when you don`t use it for long? I think for a `98 a couple second rattling is not the end of the world after a 2-3 month resting.

No, it only rattles at start-up when the car sits for a while. Once the rattle is gone, it's gone for good if I drive it again within 2-3 days.

[Seadweller]

Originally Posted by JFP in PA

1. Because the chain ramps are worn.
2. Yes.
3. Won't hurt, but will not help if the ramps are worn.

Easiest way to find out is check your cam deviation values, if they are high, the ramps are worn.

Thanks JFP. Is there much involved with checking the cam deviation? At what value would you consider the result to be "high"?

[Seadweller]

By the way, if the car has sat for a period of time, is there any harm in pulling the fuel pump fuse, and turning the motor over a few revolutions to pressurize the system before starting it?

[Starter986]

Originally Posted by Seadweller

By the way, if the car has sat for a period of time, is there any harm in pulling the fuel pump fuse, and turning the motor over a few revolutions to pressurize the system before starting it?

I hyear what you're saying... but, in my limited knowledge, believe it isn't going to help much.

You've got those three hydraulic tensioners that "pop up" to put pressure on the chains riding on the rails. They're going to "flop around" a bit until the oil pressure is enough to mate the chain with the rails. I believe that whether the car is running or not... those chains are going to flop around.

My car does the rattle upon a cold startup. Once the car is warm, and it has sat for a few hours or better... and I go to start it... the rattle is absent.

I believe pulling to fuse isn't going to reduce any wear. Have the cam deviations checked... see what you;re looking at... and go driving.

[JFP in PA]

Originally Posted by Seadweller

Thanks JFP. Is there much involved with checking the cam deviation? At what value would you consider the result to be "high"?

A Porsche specific scan tool like the Durametric system can read it, specs are +/- 6 degrees.

[Seadweller]

Awesome, thanks gang!

[ToSi]

not meaning this suggestion to become an inadvertent oil war - but if you're willing to deviate from the manual, try 15W50 Mobil 1. It makes for much quieter starts in my experience. My theory is that the thicker oil doesn't drain from tensioners when the car sits. Florida is generally warm enough that any reduction in cold flow won't be a concern.

[lkchris]

Here's one possibility for dealing with the rattle It may be a short lived solution.

For cars with metal spin on oil filters, you get a new anti drain back valve every time you install a new filter.

For the 986, the anti drain back valve is in the plastic filter housing.

You can go to dealer or shop Pelican and obtain a new plastic housing + filter + o-ring as a single part number.

With a new anti drain back valve you may notice less or no startup rattle. My experience says this may or may not last until the next oil change.

But, there has to be a reason why Porsche packages this "kit."

https://www.pelicanparts.com/More_Info/99610702055.htm?pn=996-107-020-55-M100&bc=c&SVSVSI=0784

[JFP in PA]

Originally Posted by lkchris

But, there has to be a reason why Porsche packages this "kit."

https://www.pelicanparts.com/More_Info/99610702055.htm?pn=996-107-020-55-M100&bc=c&SVSVSI=0784

Because of the number of cracked plastic housing from either road debris or mishandling during oil changes.......................

[lkchris]

Originally Posted by JFP in PA

Because of the number of cracked plastic housing from either road debris or mishandling during oil changes.......................

AND the fact the anti drain back valves don't last forever