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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30174
Location: Hertfordshire and Hampshire


PostPosted: Thu Jul 07, 2011 1:21 am    Post subject: What REALLY breaks your IMS ... Reply with quote

I have been asked if it is better for a M96 or M97 engines (that's the standard 986,996,987.1 and 997.1 blocks) to run high viscosity oils, like 10w40.

And the short answer is no.

The reason is the favourite bête noir of the water-cooled flat sixes - the IMS (intermediate shaft).

Excluding the new Gen 2 MA.01 and MA.02 DFI engines, which cleverly circumvent this issue by not having an IMS!

The M96/M97 are VERY oil hungry, but only thin oil hungry.

The oil not only lubricates and cools as in any engine, but it also runs some very important systems:
    Hydraulic tappets (for valve control from the cams)
    Variocam (all models - eg 996 3.4/3.6) hydraulic chain tensioners (for valve timing control, must be in equilibrium to balance IMS)
    VariocamPlus (later models - eg 996 3.6) hydraulic cam lobe actuation (for valve range control)


The later VariocamPlus requires far more oil for its hydraulic actuated systems than Variocam only.

Low oil levels and low oil pressure (at idle when the engine is hot) can result in some or all systems inside the engine being starved of oil.

Lack of oil to these systems (which control the valves etc) will at best cause increased component wear and reduced operating life, at worth their destruction and ensuing catastrophic engine failure.

It is the oil pump at the end of the IMS that puts the biggest rotational stress on the IMS. However, ironically, it is the oil pump that actuates the Variocam system that needs to be supplied with equal, stable and sufficient oil and oil pressures to prevent IMS imbalances (lateral stress) and bearing stresses!

Ignore all the numerous IMS and IMS bearing and IMS seal modifications that Porsche made over the years (three just during the 996's lifetime, two more in the 997's lifetime, not including its final removal).

None of these fixed the problem: they were attempting to cure for IMS stresses, not a prevention of them.

The THREE most probable reasons that could cause IMS failure are:

1) Manufacturing fractures to bearing/bearing cage or shaft - this is "discovered" quite quickly during the engines life and is almost instant in its failure mode. Usually only affects one batch of bearings or shafts. IMS failures have spanned a DECADE. This is not likely to represent a common cause over time. Under German and US laws Porsche would have to document the issue to the relevant TuV/DoT regulators. No such documents have been filed.
2) Out of balance shaft due to manufacturing or build alignment - this would cause the bearings to rapidly wear, wear unevenly and eventually collapse. However, the noise created by an out of balance IMS would be unmistakably evident on start up. The engine would run badly as the valve timing would-be out and would trigger the DME to illuminate the CEL (engine warning) to full emergency FLASH mode (warning of impending disaster). This would allow an observant driver enough time to turn off the engine before it explodes. Again, if this were to occur, once the engine had been returned to Porsche and investigated, under German and US laws Porsche would have to document the issue to the relevant TuV/DoT regulators. No such documents have been filed.
3) Lack of engine oil to hydraulic systems - this is caused by both true low oil, the wrong oil and instantaneous low oil (starvation) during start-up, high hydraulic use and high-G cornering etc. This is the most likely cause of the intermediate bearing collapse. This is NOT to be confused with the oil (grease) in or not in the IMS ball-races, this is the hydraulic and general oil system the IMS pumps and uses to balance itself (or at least without, becomes imbalanced).

(3) has no other cause other than the owner or driver's use or abuse.

Porsche partially recognised this oil significance and bumped up the 996 crankcase capacity by another 6% (0.5 litres) in MY1999 and also modified the bearing housing (this is in addition to the three 996 direct IMS mods).

So, the oil should always be filled to the brim (so to speak), we know that (and can handily check from the driver's seat without even pulling the dipstick, you have no excuse!).

But what oil?

Well Porsche is pretty specific and unequivocal about this: 0w40.

Yes, it is thin and, yes, that means it can leak (especially with an old or ill fitting RMS), but to not bother getting to the cause and rectifying seals and gaskets or simply tightening block bolts etc by bodging with a thicker (non-leaky) oil is inexcusable.

The "0w" in that code means it is exceptional thin when cold.

This is when the engine is at most stress, the pump is at most stress, the engine is unlubricated, all those hydraulic systems (tappets, Variocam, VariocamPlus etc) are all unpressurised and ineffective.

So help it out: the "0w" (low viscosity oil) will operate all its hydraulic systems as quickly as possible and get around the engine quicker and hence reduce your start-up wear.

Most importantly, when it comes to the IMS, the super thin "0w" will be less stress on the pump at the end of the shaft and will balance the Variocam tensioners across the IMS quicker, and hence reduce IMS bearing stress.

Because of all this, DON'T rag it cold either, or even "warm", wait until it is good and hot (at operating temp and oil pressure <2 bar at idle), then the oil is even thinner. That oil pressure gauge is saying how much stress the pump and IMS are under. Try to minimise it.

In the words of Swiss Tony:
"Driving a Porsche is like making love to a beautiful woman - make sure she's hot and wet before the rough stuff" (or something like that)

Here is the IMS and the oil pump, and the Variocam tensioners and the VariocamPlus cam control and the valves etc etc:

 
  
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Richard H
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Joined: 29 Jun 2008
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PostPosted: Thu Jul 07, 2011 8:03 am    Post subject: Reply with quote

Hmmm. I can see this one running for a long time. I just have two immediate thoughts which I will share, and then go away.

Quote:
It is the oil pump at the end of the IMS that puts the biggest rotational stress on the IMS.

Are you suggesting that the power taken to drive the oil pump is greater than the complete valve train?

Quote:
Well Porsche is pretty specific and unequivocal about this: 0w40.

How come there are more 5W40 oils than 0W-40 on Porsche's Approved Oils List?

Get Me Coat
 
  
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NXI20
Paul Ricard


Joined: 02 Feb 2008
Posts: 3375
Location: South Bucks

2004 Porsche 996 GT3 Mk2

PostPosted: Thu Jul 07, 2011 8:09 am    Post subject: Reply with quote

Good job we have a different engine design Richard Very Happy

I have used 5W-40, 15W-50 & (currently) 10W-60 without issues other than the recommended 0W-40 which makes the engine sound like a bag of spanners on cold startup & produced smoke.
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
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Location: Hertfordshire and Hampshire


PostPosted: Thu Jul 07, 2011 8:50 am    Post subject: Reply with quote

Richard H wrote:
Quote:
It is the oil pump at the end of the IMS that puts the biggest rotational stress on the IMS.


Are you suggesting that the power taken to drive the oil pump is greater than the complete valve train?


No, I was comparing the variable torque effects along the axis perpendicular to the IMS (ie yaw moment).

The IMS in theory is purely rotational, but of course if that was all its operating stresses were (ie turning round and round perfectly along its axis) then it would never bother the bearings laterally.

In terms of applying any lateral stresses, that is down to any inequality in chain tensioning (or other force imbalance at the end of the IMS). The pump applies only rotational stresses.

Of course the valve train itself is run off the IMS rotation aswell (that is its only method of power/motion delivery), but in this sense of what stresses the IMS and the oil you use (which was the OP's question in my PM and prompted the post), relatively consistent and non-oil dependent rotation and valve operation are not relevant, or at least out of our "oil" control.

Richard H wrote:

Quote:
Well Porsche is pretty specific and unequivocal about this: 0w40.

How come there are more 5W40 oils than 0W-40 on Porsche's Approved Oils List?

Get Me Coat


Well, Porsche have a lot of older design cars and worn out cars to cater for (and compromise all the wear, tolerance, oil pressure and pump stress/power sapping characteristics).

To be fair, the OP inquired about 10w40 (which is most definitely the cowboy mechanic's leak prevention).

By that definition 5w40 is the compromise!

All NEW engines and engines that are as "good as new" (and are yet to be otherwise compromised) are stipulated as 0w40 in temporate or cold climes.

I guess it doesn't matter what "Xw" you use in Namibia Dont know
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
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Location: Hertfordshire and Hampshire


PostPosted: Thu Jul 07, 2011 9:19 am    Post subject: Reply with quote

NXI20 wrote:
Good job we have a different engine design Richard Very Happy

I have used 5W-40, 15W-50 & (currently) 10W-60 without issues other than the recommended 0W-40 which makes the engine sound like a bag of spanners on cold startup & produced smoke.


The GT1 blocks are different (as you pointed out) and famously smoke on thin oils.

Additionally, the advice here is not aimed at racing or continuous high load scenarios, but sadly the prosaic normal use of 99% of Porsches (and the owners/drivers who perhaps don't care or know too much about how to use or not abuse their cars).

Half of the importance of the above post was to make sure the "sump" was fully filled (real dry-sumpers: not relevant Wink), then what with.

In that sense it is probably more important you have enough oil, than with what oil!
 
  
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monty
Montreal


Joined: 19 Nov 2010
Posts: 557



PostPosted: Thu Jul 07, 2011 10:11 am    Post subject: Reply with quote

"Driving a Porsche is like making love to a beautiful woman - if you don't want to put undue strain on your shaft, wait until she's well lubricated"

Last edited by monty on Thu Jul 07, 2011 10:32 am; edited 1 time in total
 
  
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davo-davo
Monza


Joined: 25 Jul 2009
Posts: 191
Location: Tyne & Wear


PostPosted: Thu Jul 07, 2011 10:32 am    Post subject: Reply with quote

Excellent post GT4!
Very informative to us laymen as to the use of high or low viscosity oils and in which circumstances they should and shouldn't be used.
Cheers!
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Stuart
General
General


Joined: 16 Sep 2007
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Location: Waterworld

2004 Porsche 996 GT3 Mk2

PostPosted: Thu Jul 07, 2011 11:03 am    Post subject: Reply with quote

On my Hartech rebuilt engine (read good-as new) they put in 10W-40 Castrol Magnatec and have since done a change using the same. They've advised me that this is their preferred oil and weight for rebuilt engines. I've also asked about oil pressure after a couple of Ring hot-laps. In the past I've noticed oil pressure can go as low as 0.5bar at hot idle using 40 weight. Myself (and a few 911uk others) changed to 50 to try and counter this.

GT4, in your mind, stick to 40 or change to 50?

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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30174
Location: Hertfordshire and Hampshire


PostPosted: Thu Jul 07, 2011 11:22 am    Post subject: Reply with quote

As engines wear you can get away with (or even require) higher viscosity oils.

Additionally, as per the racing models (GT3 etc), you should run higher "operating" temp viscosity oils as your operating temp is now on average higher (this is complicated by modified thermostats etc).

So viscosity wise, high temp Xw50 = normal temp Xw40 (would be a rule of thumb)

The exact conversion would require the characteristic oil spec document and the exact (average, peak, representative) temps you will be running.

I would imagine a rebuilt engine is still slightly over-sized in comparison to factory spec (ie tolerances in new aftermarket liners and pistons are not likely to match the tolerances of mass produced factory items, which ironically results in higher average quality metrics).
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30174
Location: Hertfordshire and Hampshire


PostPosted: Fri Jul 08, 2011 5:14 pm    Post subject: Reply with quote

I wasn't able to answer Baz's questions as the other thread was locked.

That and an inundation of PM requests to answer about oil, thermostats and IMS prevented me from replying in time.

However, here is some info on low temperature thermostats:

http://www.lnengineering.com/lowtemperaturethermostat.html

looks like this:



OEM price £26+VAT, LN price circa £80

whole housing:



location:



click for big:

http://www.911uk.com/files/tstat_pet_162.jpg

It's a Boxster, but this should help to understand where it is:

http://www.pelicanparts.com/techarticles/Boxster_Tech/34-WATER-Thermostat_and_Pump/34-WATER-Thermostat_and_Pump.htm
 
  
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wizard993
Donnington
Donnington


Joined: 23 Jan 2008
Posts: 11982


1966 Singer Gazelle

PostPosted: Fri Jul 08, 2011 6:55 pm    Post subject: Reply with quote

http://www.epsparts.com/contents/show/ELF-Total-Lubricants-Product-Information-Page

The best heat management system you can deploy for an engine(within reason) the better. On a 911 Total oils help to keep temps under control, as does the thermostat and keeping the rads clear.

Crap oil or oil that's been in a while often shortens the IMS bearings lifespan. A better/efficiently managed coolant system also helps preserve the ability of the oil to do its job. Exceses heat/heat spots on areas of the engine breaks down the oil properties, leading to possible bearing failure.

I am convinced that it's not the IMS that's fundamentally at fault, It's the 996/997 cooling abilities that starts the chain reaction. Helping the cooling system to do its job/keeping the engine cooler and the oil in good nick is, IMO the secret to having a trouble-free 996/997 experience.

A friends who has a big Citreon was using fully synthetic Mobil oil. His oil temp dropped ever so slightly when it was replaced with Total oil so this oil does help lower/absorb temps better.
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30174
Location: Hertfordshire and Hampshire


PostPosted: Fri Jul 08, 2011 7:15 pm    Post subject: Reply with quote

Does the IMS have a bearing?
 
  
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318touring
Spa-Francorchamps


Joined: 21 Jan 2011
Posts: 261
Location: Wellington, New Zealand


PostPosted: Fri Jul 08, 2011 8:04 pm    Post subject: Reply with quote

How much Hartech charges for their low temp thermostat? Can't find it in their website.
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30174
Location: Hertfordshire and Hampshire


PostPosted: Fri Jul 08, 2011 9:38 pm    Post subject: Reply with quote

If he hasn't changed the business model, you have to have supply and fit, the thermostats aren't released for supply only.

For comparison the LN item is $80 thermostat only, $120 for thermostat and housing.

Obviously those are US prices, not advocating their purchase as that would incure delivery and duty, they are just for illustration.

Incidentally, OEM thermostat is circa £26+VAT.
(of course that is just the normal 190oF tstat, not the 160oF tstat you need)
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8369
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Fri Jul 08, 2011 10:57 pm    Post subject: Reply with quote

318touring wrote:
How much Hartech charges for their low temp thermostat? Can't find it in their website.


Looks like you will have to order from the States, I was thinking the same and couldn't find a price for the Hartech Stat.
Being in NZ you would have to import anyway.
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wizard993
Donnington
Donnington


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1966 Singer Gazelle

PostPosted: Fri Jul 08, 2011 11:03 pm    Post subject: Reply with quote

it sure does Gt4...thats where the problem starts. Once the bearing goes the shaft starts an imbalance that wrecks the cranks....and the engine turns to toast
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GT4
Nordschleife
Nordschleife


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Location: Hertfordshire and Hampshire


PostPosted: Fri Jul 08, 2011 11:34 pm    Post subject: Reply with quote

I can't tell if you didn't get me kidding you or you are kidding me Confused

I'm sure the problem starts with extra stresses on the IMS over-working the (sometimes borderline) adequate bearings and the fact Porsche seal the bearings for life, but actually either sometimes the retained grease can't cope or on a minor seal breach the grease washes out, but isn't effectively replaced by enough flow of new lubricant.

The usual method to cater for the higher than design tolerance stresses on the bearings is to fit better and stronger ones, or convert the original bearings to a fully open design by removing the seals to allow a continuous flow of nice new cool and refreshing oil. Of course preventing instantaneous over-stresses at start-up can be achieved by using an oil with a thinner cold grade and not over-loading the pump or delaying stabilisation of the hydraulics systems that need to be pressurised and activated ASAP at start-up.
 
  
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318touring
Spa-Francorchamps


Joined: 21 Jan 2011
Posts: 261
Location: Wellington, New Zealand


PostPosted: Sat Jul 09, 2011 4:39 am    Post subject: Reply with quote

Yes gents, that's what I thought re -Hartech. I was looking around their website to see whether they do export their thermostat.
 
  
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GT4
Nordschleife
Nordschleife


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PostPosted: Sat Jul 09, 2011 9:22 am    Post subject: Reply with quote

160oF thermostat is $99 USD at LN Engineering.

INSERT:


If you plan to do it yourself you need the thermostat AND tool which is $108 USD (a Porsche specialist should already have this, in fact depending on how specialist the tool is it may be generic to fitting these sorts of thermostats for any garage that looks after coolant systems, but you'll have to check with LN Enginerring what the tool is or looks like).

The easier way in a sense is to buy the thermostat already fitted in its housing (which is a bit of a waste of the old housing and costs a bit more).

The advantage is the housing just bolts straight on and you fit the outlet pipe.

The thermostat and housing are $170 USD.

THERMOSTAT AND HOUSING


See the LN Engineering online shop here:

http://www.lnengineering.com/store/catalog/boxstercayman911-models-c-36.html

[EDITED - as I can't read and posted the wrong prices initially]

Last edited by GT4 on Sat Jul 09, 2011 10:58 am; edited 1 time in total
 
  
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MisterCorn
Dijon


Joined: 08 Jan 2011
Posts: 7202
Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Sat Jul 09, 2011 9:39 am    Post subject: Reply with quote

Is there any advantage to doing this on a turbo, or is this purely recommended for N/A cars? I am looking at getting some mods done to my car which will increase the power and wonder if this is one to add to the list.

MC
 
  
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