I'm sure there are plenty of threads on this, but why not start another...

I'm a 996 C4S newbie. My car needs fresh fluids.

What's the consensus on:
- engine oil
- manual transmission oil
- differential fluid

My car has 150k miles and enjoys drinking oil to the tune of 1 quart per ~1500 miles. I live in California and my car only comes out when it's above 50F. Per the owners manual, I can use either 10-40, 15-40, 15-50.

These days, those grades aren't so easy to find. The thickest synthetic I can find at Costco is Mobil1 10-30. I generally avoid Walmart as a matter of habit, but I have noticed that they have a pretty good selection of 5 quart synthetic jugs from Mobil1, Total, etc. including some thick stuff. Any suggestions?

I have had good luck with Redline lubricants for transmission and differential fluids in my BMWs. In general, I replace transmission fluid every 30k miles and differential fluids every 60k miles. What are the go-to choices for 996 transmission and differential fluids?

I'm a 911 newbie. So here goes. I assume my 996 C4S has a unitary transmission/rear diff and a separate diff for the front axle. Is that correct or am I an idiot?

Assuming I'm not an idiot, what sort of fluids should I put in the tranny and front diff? In BMW-land, it was Redline D4 ATF in modern manual transmissions and Redline 75/90 in the rear diff.

I recently purchased a very strange car with an engine located behind the rear axle and that appears to drive all four wheels. If this weirdness continues I should seek out a Tyrrell 6 wheel F1 car.

Best regards,
Eric

 

Okay, let me take a stab at this. For the oil, any Porsche Approved A40 spec is okay, and there are quite a few, should be 0-40, 5-40, or 5-50, I use DT40 in 5-40. Redline fluids are good, just ensure they meet Porsche spec/requirements.
1 quart per 1500 miles seem like a lot, I can go 3-4000 and only consume 1 bar, which is a 16th of a quart. Transmission fluid for a manual, try Mobil Delvac 75W-90, factory fluid is made by Shell.


The 996 C4S uses a VC, Viscous clutch, in "series" with the driveline to the front diff'l. It is my understanding that the VC is always "stiff" enough to couple about 15% of the engine drive torque to the front diff'l but the coupling level will increase to as much as 45% if the rear tires slip/spin for an extended period. The VC does not react instantaneously to rear wheel slippage. Additionally you have a "virtual" rear LSD, Limited Slip Differential in that the rear brakes will be applied, differentially, to the wheel/tire with the most slip/spin. On top of all that you have traction control which will apply braking to BOTH rear wheels if they both slip/spin.

 

With 150K miles on the car and I assume the car passing a used car check out with flying colors before you bought it my advice would be to stick with the fluids that were used to get the car to 150K miles. They seem to be working just fine.

Thus in short replace the fluids with the same fluids.

BTW, the info in the owners manual regarding oils is wrong. I don't think Porsche has updated that section since the early air-cooled days.

My Porsche tech when I ask prints out an approved oils list for me. This is available online at another forum if you are a member.

The only Porsche approved oils are viscosity grades 0w-40 (a must if you operate your car in cold (-25C) temperature), 5-40 and 5w-50. Of the latter I think there is only one approved oil with this viscosity.

(FWIW, where I live/drive because it doesn't get very cold -- 27F a few days ago -- and it gets quite hot (triple digits often in the summer) -- I switched both of my cars to Mobil 1 5w-50 oil. But they both were fine even in 116F to 118F heat with 0w-40 oil, albeit changed every 5K miles).)

Without the list if you want to buy oil off the shelf at a local auto parts store or at Walmart look for "A40" on the bottle. This is an indication the oil meets with Porsche's approval for use in its late model sports cars.

For the tranny/diff fluid I have the Porsche service department tech use the factory stuff. I hate the smell of tranny fluid and don't have the facilities (or time or desire) to change this fluid myself. The factory fluid is pretty good in my book as my 2002 Boxster has accumulated nearly 300K miles on its original transmission/diff with factory fluid changed at the recommended intervals or a bit sooner.

Your car and my 996 Turbo share the same AWD system and I believe the tech uses the same diff fluid in both rear and front diffs. As with my Boxster I have the diff (and tranny) fluids done at the dealer and just let the tech use the factory fluids.

Oil consumption varies. One quart per 1500 miles is a bit on the high side of oil consumptoin but not by a worrisome amount. How you drive the car plays a role too. Honestly, I just wouldn't worry about it. Just be sure to keep some oil on hand and keep the level topped up. You do not want the level to get too low. Generally I add oil when the level gets low enough a full quart is required. This way I don't have to keep an open bottle of oil in the car trunk. I'm always worried about the thing leaking and making a mess.

But if I head out on a long road trip or for a bit of spirited driving I top up the oil level to the max line just to ensure the engine has a full load of oil.

Be aware the AWD system is not like some other systems. Torque is transmitted to the front diff via a viscous fluid coupling. This viscous fluid requires heat to become viscous enough to transmit torque. It gets its heat from molecular friction by a series of driving and driven discs in the coupling. Nominally the amount of torque transmitted is in the 5% to 40% range. 5% occurs at slower speeds but I don't know what the cut off is and there may not be one. Porsche doesn't say "0%" so maybe 5% occurs even at a slow roll? The 40% transfer occurs at (Porsche says) 150mph.

Just be aware this is not a car to if you get stuck somewhere and the rear wheels are spinning to keep doing this in hopes the front wheels will pull the car out of the stuck spot. All you will succeed in doing is ruining a very expensive viscous coupling/front diff.

Also, just in case it the car ever needs to be towed know the car can't be towed on just its front or rear wheels but must be flat bedded with all 4 wheels off the ground.

 

I have a copy of the Porsche Approved A40 Spec oil list if you want it.


This is true;
Just be aware this is not a car to if you get stuck somewhere and the rear wheels are spinning to keep doing this in hopes the front wheels will pull the car out of the stuck spot. All you will succeed in doing is ruining a very expensive viscous coupling/front diff.


The cost for a new one installed......$9000.00 give or take.

 

Thanks for the great responses. I was planning on doing some mud-bogging, but now that I know it will cost me $9000 I'm going to leave my pretty little sports car in the garage through El Nino.

Just to clarify, I know our cars have an engine and a transmission. Beyond that, I'm not sure. Is there a separate rear differential, or is that integral to the transmission? Is there are separate rear/front transfer case, or is that integrated into the front axle diff?

I want to replace all the dirty fluids in my car. The first thing is figuring out how many components there are in this drivetrain. Then I can research the right fluids to replace them with.

From my research, oil consumption of 996s varies widely. Anything more than 1000k/liter is considered normal per Porsche. Crazy.

Thanks!

 

"Just to clarify, I know our cars have an engine and a transmission. Beyond that, I'm not sure. Is there a separate rear differential, or is that integral to the transmission? Is there are separate rear/front transfer case, or is that integrated into the front axle diff?"


Yup, it's called a "transaxle"...i.e. Transmission/Differential in one - axles connect directly to it. http://www.autoatlanta.com/porsche-p...section=302-00


and the front drive... http://www.autoatlanta.com/porsche-p...section=305-15


http://www.autoatlanta.com/porsche-p...section=305-10


Good Luck

 

Thank you.

Is the front diff a regular service fluid or "lifetime" fill? Maybe I should just leave it alone. I like to do diff fluid every 60k miles in my BMWs, transmission fluid every 30k. I've never even had to replace a clutch, let alone a diff or tranny. What's the proper diff fluid?

 

"Lifetime" ? You mean like our coolant? ;-) Remember, when these cars were new, Porsche was telling us we could go 15,000 mi. between oil changes on Mobil 1... I don't think anyone is doing that any more... For all intents and purposes, there is no such thing as a "lifetime fluid"... I think most experts (of which I am not one...) agree this is simply marketing hype. I don't know an exact # for differential oil, but 60,000 mi. seems pretty reasonable to me. Of course there are many variables which will affect the life of diff/gear oil - driving style, driving frequency etc. etc. etc... As long as you stick with quality oils/fluids and "reasonable" service schedules you'll be fine. Good luck

 

Coolant. not supposed to mix brands, only the authorized $$$40 a gallon stuff.

As long as a coolant meets euro specs, it's good as far as I'm concerned.


or Suddenly the Gel monster will show up?




$40 a gallon should be Pope blessed and packaged by naked virgin nuns.


good read, YMMV


http://rennlist.com/forums/996-forum...olant-why.html




My 996 c4s just developed a slow seep leak from 3/4 ways up the front right radiator. Don't know if I took a rock into the fins, or a upper hose clamp? How rugged are these?


To pull the radiator, can I do it from underneath or does the whole front bumper skin and lower spoiler have to come off?

 

I've been running Redline 5-40 in the motor, 75-140 in the dif, and 75-140NS in the tranny since I bought it with 25K mi on it. Now almost at 140K mi. The motor only uses 1/2-1qt per 10K mi. I change the driveline fluids every 50K.

 

My long time German car parts source (BMA parts in Glendale CA), suggested:

5W-40 Liqui Moly full synthetic motor oil ($35/5liter bottle)

Liqui Moly 2048 75/90 full synthetic ($15/liter) for both transaxle and front diff

what do you guys think?

What are the capacities for the transaxle and front diff?

 

I just changed my transaxle and front diff. fluids. Never again. The old oil STUNK.
It still looked good, just a stinky oil. Funkified my whole shop. I used to live near oil refineries, so I'm used to the smells of oil/gas production. The new oil (Mobil Delvac) had a similar odor, but much less so.
Good luck with your new car.

 

It's $40/gal. for the full strength/concentrate stuff - you mix it 50/50 with water, so it's really only $20/gal. for the "coolant/anti-freeze"...i.e. 1 Gal of the concentrate makes 2 Gal. of "coolant"...