Has anyone out there replaced their 4.8 alternator, and has anyone gone to an air cooled unit? Mine died today and I'm wondering how much work it will be to replace. I'm a pretty good wrencher, but I don't want to spend forever doing this. Any advice will be appreciated.

 

If you do a bit of searching - there is a thread on someone doing this. It's a bear of a job - took at least a full day (is that forever? What's your skill level?), and as far as going to an air-cooled unit - it won't provide the power the Cayenne needs to keep running. The existing one is water cooled for a reason (the capacity and the location of the alternator means an air-cooled one would overheat rapidly and destroy itself.)

 

Thanks for the info. I'm pretty good with a wrench, rebuilt a few engines in my youth, but that alternator is so buried that I'm at odds where to start. i couldn't find a link or video, and I'm hoping that the whole nose doesn't gave to come off to get to it. Perhaps it can be done from below. guess I'll just have to keep looking.

 

just took the car off the charger. alternator worked for about 4 minutes and then began to dip again. i'm wondering if my 10 month old battery has lost a cell?

 

You won the alternator game. You get to jack the front up, remove the front wheel and liner, unhook the radiator and dump your coolant, remove the headlights and front bumper, put the car in lock mount service position and then swear while hooking up the new alternator in the correct orientation with its wires in the heat shield. Just be thankful you don't have a turbo right now or you would also be dealing with all that plumbing too! Definitely a pain in the ***, but there is nothing to the coolant lines. Just make sure you buy new ones because the old ones will be brittle and crumble in your hands. Do it right the first time, because I promise you won't prefer to do it twice. Good luck.

 

That would be the first thing I would check before I dove into the alternator abyss.

 

My alternator came and went a few times before it ultimately failed. Start part shopping before you kill the battery too. I am still wondering if the voltage fluctuations from this were what led to the death of the transformer in my gauge cluster.

 

People have reported bad results with rebuilt alternators and with replacements that arent made by Hitachi, the supplier Porsche used. Circa $1500 or so from a dealer just for the part. You can find it online for a little less than $850 for a new Hitachi.

Define dipped... my recently replaced alternator spends time running at 13 volts, possibly even a little less. Next time I look, its at 14 volts or a little higher. Goes up and down in the normal course of driving with a known good alternator and a known good AGM replacement battery. Don't use a lead acid wet battery... AGM is much safer if there is, heaven forbid, a roll-over. Oddyssey and Optima spiral cell batteries are even better, but get a little pricey if they even make an H9 size.

If you are having trouble keeping the battery charged, you may have 1 or more plugged up roof drains. That causes water to drip inside the car and it often finds a connector or splice where the water can drain power from the battery constantly. Check under front and rear carped for dampness-- and in low spots of the cargo area. You may not be able to feel dampness through the carpet unless water is sloshing around. Most of the time you need to lift the carpet and insulation under the carpet. There is some description on how to find the outlets for the drains in this forum, a search should turn it up. Search for: roof drains. Some people have chosen not to put the little crimped caps back on the drains since it seems like those are responsible for the clogged drain in the first place.

How old is the battery? They tend to last 8 years or so in average climate, maybe a little less where it gets very cold, and maybe a little less in extremely hot areas. If it is a Bosch battery it may be original, should be a date of manufacture label on every battery. Also, almost every battery chart says H8 is the battery size. If you have an H8, it is shorter in length than the correct battery size... H9. There are YouTube videos showing how to access the battery under the left front seat.

 

If your battery lost a cell you would see a dropped resting voltage on the battery and probably notice some odd electrical behaviors while starting or running accessories with the engine off. What voltages are you seeing when the car is running and where/how are you measuring it?

 

Just curious if you had a coolant pipe or reservoir failure in the last year on this vehicle?