First I would not think oil viscosity would have anything to do with a RMS leak... but recently after switching to Mobil 0-40 from 15w50 it is leaking!

Is this just coincidence, or does my 996's previous owner knows a trick to prevent a leaking RMS?

 

This is debatable, but I, for once, believe it encourages seal leaks. I also do not believe you should be running 0W40, regardless, in your neck of the woods. Run 15W50 all year.

 

0w40 was recommended by several CA dealer mechanics. The engine revs a lot happier with the 0w40 and the gas mileage went up also.

 

First I would not think oil viscosity would have anything to do with a RMS leak... but recently after switching to Mobil 0-40 from 15w50 it is leaking!

You are right, one has nothing to do with the other. You can however sometimes mask an oil leak by going with an oil which has a higher viscosity. You probably have a very tiny leak which is "cured" by the 15W50 oil.

 

It is true that, when cold, your engine will have to work less when you use the 0W40 oil compaired to 15W50. However, once you reach operating temperature, there is no difference in performance, but there IS a difference in the level of protection. All materials contract and expand as a result of temperature, including crank, block and seal. If at the time these changes in size, there is water (0W40) being splashed about, there is an increased chance that some of this oil will find it's way between the seal and engine. As this process continues, the seal will begin seperating from the crank and block. This seperation will be immeasurable, but the thin oil barrier that now is between the seal and block and or crank will not hold the extreme pressure created by the engine at high rpms. This will encourage oil, high crankcase pressure is present, to begin seaping past the seal, more and more until a permanent, non presurised leak developes.

For this reason, not only do you need to engure that engine pressure is minized until full warmup, but you need to you an oil somewhat thicker than water.

 

The internal oil passages were sized for the flow characteristics of 0W-40 synthetic oil. While it doesn't get cold enough in Chino Hills, if you were to drive up to Yosemite or Reno to go skiing and leave the car out overnight in subzero temperatures you and the engine would definitely know the difference in the morning. Porsche determined that a number of engine failures were due to inadequate lubrication in cold conditions. Because of the high viscosity of 15W-50 in cold conditions there was inadequate oil flow resulting in bearing failure. There is a reason why Porsche recommends 0W-40, and a very good one.

 

The oil passages were sized for 0W40 oil? I thought I heard it all. I guess the oil passeges in my car (which was factory filled with 15W50) must have shrunk so it only can fit 0W40 now? Remember, Porsche DOES NOT recommend 0W40 oil, but only includes it on the "approved list". And this list has changed half a dozen time or more over the past few years. The egines have not changed. The oil has not changed. Just their approved list has changed. So, did Porsche make a mistake when they approved and filled the earlier 996's with 15W50 or are they making a mistake now. I know that many think Porsche knows all things, but it is very clear that, in the case of the oil they use in these cars, that they have made a mistake. You just need to deside when that mistake was made.

 

Here's my take:

I change my oil/filter at every 5000 mile intervals, Some may say that is too soon but it's what I do.

Twice I used 15/40 and the leak persisted. So I went back to 0/40.
My 7th RMS suddenly stopped leaking about 6000 miles back and has not leaked since. I did an oil change about 1000 miles back and still no sign of any oil leak. The 7th RMS did however leak for several thousand miles after fitted. It just stopped all on its own.

The only thing that has changed is that I changed job back in August last year. The new job requires that I commute to Cambridge from Liverpool each week (about 220 mileas each way). The oil leak stopped around August/September. It may be just a coincidence but I think the reason it stopped is that I now use the car more. I do a minumum of 500 miles each week and its at motoroway speeds. So maybe the answer is that parking the car up after short jeourneys is the cause. I dunno.

Anyway, it would seem, I am RMS trouble free at last!!!

 

This was almost identical to what the Porsche dealer mechanic had told me about using 0w40s. He also told me that all the dealers are now using the 0w40 fill for the 996s, but the 993s are still using 15w50.

FWIW, I drive my 996 about 4 times a week, 30 minutes of highway driving each way. No RMS leaking problem prior, the RMS started to leak after a 4 hour business trip one day.

 

Honestly, I think it is one big crap shoot with regards to RMS. I have just about 60K now on my engine and it has been the best car I have ever owned. Not a leak EVER! Oops, I forgot, it did lead once, but that was the &#%$^&*@*! coolant tank

I do 0w-40 in the winter months (Oct-Mar) and 15W-50 in the summer months (Apr-Sep). I do most of my tracking from Mar-Oct.

 

Haven't seen your posts in a while Bernie, good to see you still around...

 

If you want something a little thicker than 0W40 but not too far off what Porsche recommends... go with 5W40 from Amsoil or LiquiMoly... they are better than Mobil 1 in terms of qualities such as antifrothing and burn less than Mobil 1 as well... the added weight won't hurt a bit since it is so close to 0W40... for me here in Canada... especially in the winters... the 15W50 is just too thick for winter startups....

or find a good 5W50 as a happy medium and see how it works out for you...

 

Cheers Torags, been lying low in my new job. But still here on the side

 

Is 5w 50 anygood? Thats all there is in Australia at the moment (well at least at Super Cheap Auto and Pep's -large auto outlets in Australia)

 

This topic was discussed quite a bit over at Renntech. A good compromise for those of us living in northern climates seems to be Castrol's 5W50. However, if I lived south of the Mason-Dixon, I would run 15W50 all year long. As is, in NYC, I just had my car refilled with 15W50 this time round (with the dealer's blessing), though I keep it in a heated garage. If it were to ever spend any significant amount of time outside in Vermont (where I ski), then I surely would run the 5W50 all year.