We have a 2006 Porsche Cayenne Turbo. Presently, it is venting oil from the front differential (via the vent hose/line). There are no strange noises or rough driving occurring, only oil venting from possible pressure and/or foaming oil in the differential housing. I should also mention that the oil level is not over-filled. Since I was told there are no sensors or regulators within the differential itself, the focus has been on two possible causes: 1) bad oil or 2) gear problem/replace differential. As part of the trouble-shooting process (and cheaper to fix), we replaced the oil hoping that perhaps this is occurring due to viscosity breakdown and overheating, but the oil had been replaced only 6K miles ago (Redline 75W-90). The Porsche dealership mechanic checked the "old" oil and found no elevated amounts of iron filings in the oil suggesting shear breakdown (plus it is not noisy nor has any other symptoms). At this point, we are perplexed as to why the differential is still venting oil. Porsche’s response to differential problems outside of changing oil is to replace the entire differential as one unit (I was told they do not rebuild or sell replacement parts at the dealership). As this is an expensive proposition and there are no other problems, I am reluctant to simply replace the differential. Any thoughts on what could be causing the problem? I am new to the forum, so please forgive me if I am not following proper protocol. Please advise and thanks for your time. - Joe

 

Did it do this at all with the original oil (before you switched to Redline)? Sounds like it's foaming up to me.

 

Thank you for your reply. No, we did not have this problem with the original oil. Roughly 6K miles ago, we changed the differential fluid with Redline 75W-90. When we started having this problem last week, we took it into Porsche and they changed the oil again, but unfortunately it is still venting oil.

 

Did they mention how the oil looked when they drained it? Is there any chance water is somehow getting into the diff case and contaminating the fluid?

 

The only time I have seen a Diff vent fluid is where there was an internal problem. The temp will rise and cause it to vent. I would suspect that there is a bearing that has failed and causing the excessive heat.

You would think it would be audible, but I have seen otherwise. Of course, I have no experience on a Porsche Diff, but I would have to think that parts are available to rebuild, versus replace. Not sure what a differential would cost from Porsche, but if in the 2k range, I would just replace versus rebuild.

Mike

 

Thanks guys for the feedback. Although there was not an excessive amount of iron filings in the fluid and no noise, the general consensus is that either there is a small chip in one of the gears causing the oil to aerate or there is a large amount of friction in the gears causing the oil to overheat. Most folks suggest that I don't monkey around with a rebuild or used differential (as either costs almost as much as a new one). At this point, I am going to bite the bullet and replace the differential with a new one as the dealership quoted me roughly $3,800 for a new one installed with a 2-year warranty. Thanks again for the suggestions. - Joe