wwest

I pulled the seat heat fuse, jumpered/bridged in a 12 volt battery charger, turned the ignition key on and released the bonnet/hood.

Blessed be the INTERNET! I had convinced myself, absolutely, that the front differential itself or bearings had failed in my 2001 C4. Nutating bearing noise at 65-68MPH and around corners and the whole bit. Luckily I had previous experience with tires going noisy after a few thousand miles. Searched the internet for Bridgestone Potenza RE730 and discovered numerous complaints of noise developing after 5k miles or so. Two or three even said they thought the noise was due to bearing failure at first. I have run Bridgestone Turanzas on my Lexus vehicles since ~1993, so I had absolute faith that the tires were't the problem. So, do I take the car to Porsche and have them "judge" the problem, knowing full well that their answer will be a function of $$ signs, or do I replace the tires on the chance they are the problem? Installed Michelin PS2s, Costco, today and the car runs as quietly as the day I picked it up at the factory.

Bridgestone sent me to Mastercare dealer here in Memphis and techician verified tire noise as the source immediately. After about an hour's discussion and multiple phone calls they agreed to a no charge upgrade to RE750's. So far I have opped to pay extra (substantial) for the RE050's but I'm wondering if the RE750 would suffice... Other than the noise the RE730's served me well. On the track at Daytona insofar as I could tell the PSM was never active. Does the new tread pattern on the RE750's really solve the noise problem?

At ~8,000 miles the factory Conti's on my 2001 C4 were EXTREMELY noisy. I installed Bridgestone Potenza RE730's but now at ~14,000 miles it sounds as if my front wheel bearings are failing. Searching on the internet I find that this is a common problem with the RE730's and Bridgestone has even made a running design change, "gen-II", to the RE730 to try and combat the noise problem. Anyone with any experience on these and getting compensated by Bridgestone? Any adverse comments on my next try, Michelin PS2's..?? And by the way, the noise is my only complaint about the RE730's. About to make the return trip home to Seattle and believe it or not I would like to hear my wife talking on the way back.

Again, the Porsche climate control system uses a airflow reheat/remix method so as to not discomfort the driver/passenger with airflow that is TOO cold. ALL air flows through the A/C evaporator and is CHILLED to as close to 33F as time, airflow speed, will allow. A portion, or all, of this CHILLED airflow is then diverted through the heating section and then all airflow is remixed before exiting the system. If the cabin is at 85F (or if the sunlight radiation sensor indicates BRIGHT sunlight) and your setpoint is 72 the system airlfow will be COOL, but not so much so as to be discomforting. As the cabin temperature declines to 72F the system airflow will become warmer until it is just cool enough (~68F??) to sustain the cabin at 72F. You can defeat the reheat/remix system by calling for max cooling and then use the blower speed to manually regulate your comfort level. You can also increase the A/C efficiency by adding a manual flow control valve (Home Depot) in line with the heater hose just to the left of the battery under the bonnet. Both of the above methods will result in less cycling of the A/C compressor, improving MPG and decreasing the heat load on the engine cooling radiators.

:drive:

If the outlet airflow is ice cold once the passenger cabin is near the setpoint then someone has shorted out one of the system sensors.

One thing, IMPORTANT!, to remember. Once the passenger cabin reaches or nears the temperature setpoint reach up and select dash outlet ONLY! Or dash and footwell if you wish and but not in recirc mode. Otherwise a major portion of the system's cooling airflow will be needlessly routed toward, and thereby WASTED, to the interior surface of the windshield. Flaw in the design that Porsche refuses to address even though VW has for the Touareg.

Modern day climate control systems, including the 996, use an airflow "remix" method so that the airflow exiting the system isn't discomforting. ALL of the system airflow first passes through the A/C evaporator and is chilled to the MAX. Then, some or all of that airflow is routed through a reheat cycle, diverted to flow through the heater core. Then both airflows are remixed. The base idea, once the cabin temperature has reached or is very close to your setpoint, say 72F, the system airflow temperature will be just below that (~65F) to prevent discomfort and now flow volume ("..it does control the level of the blowing automatically...") will be the principle method for maintaining your comfort level. It is well known within the A/C industry that the actual cooling level of the refrigerant heat exchange process cannot be modulated. The refrigerant "boils" at ~20F and any airflow exposed to that for a period of time will soon be at that level. Most systems regulate the refrigerant flow such that the A/C evaporator surface temperature remains at or close to ~35F but NEVER declines below the freezing level wherein it would soon be blocked with ice. If you want to experience airflow at its maximum cooling level then turn the system to minimum temperature and the lowest blower speed before the engine water jacket rises to operating temperature.

Removing some of the A/C load also helps, sometimes dramatically so. Coming across AR a few years ago in 100F+ heat and construction zone my C2 starting overheating. I first shut down the A/C but when that didn't help enough I stopped alongside the freeway and discovered one fan motor had failed. We drove the rest of the way home to Seattle with the A/C on but set at max cool and used the blower speed to adjust our comfort level. In max cool the airflow doesn't go through the reheat cycle and thus the A/C compressor duty cycle, and heating pre-loading of the radiators, is much lower. When I got home I installed a Ford fuel tank selector switch/valve, along with a new fan motor, so that there is NO hot water flow in the system when the A/C is functioning.

Your temperature rise is likely more a function of the flow restriction of the thermostat rather than any shortcomings in radiator cooling capacity. Unless one or both of the electric fans have failed at low or high speed I suspect that should you remove the thermostat for a few days you will find the coolant temperature never rises above 150F.

Hmmmm... My Michelin pilots did an outstanding job on the track at Daytona just before the 24 hour race. PSM/TRAC never kicked in even once. But then I try to drive the same way I fly, with my eyes and thoughts out in front, way in front.

Okay, look at it this way. lots of new cars have low tire pressure warning indications. Most of these work by comparing the rate of rotation of each wheel, using the ABS sensor signals, against a KNOWN, previously estabished, reference. What reference? Well, if you happen to RESET one of these low pressure warning systems while the tire in question is still low then a NEW (incorrect, but...) reference is established and the warning system will be perfectly "happy" unless it detects an additional change, relatively, in a tire's rational rate. I know, personally, of instances wherein someone noticed a slightly low tire, re-inflated it to spec, and the low pressure warning light illuminated as soon as the car was driven. The newly inflated tire's rotational rate no longer matched the previously established reference for that tire in relation to the other three. Disconnect the battery and be done with it!

The signals from the ABS front wheel speed, rotational rate, sensors are not comparing "correctly" with the rear sensors due to the "new" difference in overall circumferance of the rear tires. Unplug the battery for 15 or 20 minutes but be sure you know the radio security code first.

You can radically increase the A/C efficiency by installing a shutoff valve in the heater water supply line in the battery compartment. Also be sure the A/C compressor is not being cycled off by intermittent engine water jacket excusions into the "almost overtemp range. On a hot day in slow traffic it takes both front radiator cooling fans, capable of operation at BOTH speeds, to keep the engine water jacket temperature within the range wherein the A/C remains enabled. If the fans' low speed mode does not work by the time the water temperature rises to the level of activating the high speed mode the water jacket will go overtemp for a short period.

My 2001 C4 did that, exactly, just after leaving Daytona in Feb. Turned out to be a bad cell in the battery. The only other indication I had was that the engine seemed to crank a little more slowly than I remembered but always fired off.

WOW...!! I wonder how good a business might it be of providing artificial sound enhancement via the in car sound system but synchronized with the engine RPM/loading/gear ratio. Better and a lot less expensive than using a 300HP engine to produce 300 watts of sound power. A set of earphones on the driver and we could get by with as little as 3 watts. Bose sound cancellation headphones in reverse! $300 a pair or priced equal to an otherwise useless K&N retrofit?

No, not magic. And yes, you're right. If I have the setpoint at 71 and the system is cooling the windshield I can reset it to 73 and it will not not. Until the passneger cabin air temperature rises to the new setpoint. The windshield heating system in the 707, and many other Boeing jetliners, track the outside temperature and raise the windshield heating level accordingly. Most common failure is actually windshield cracking due to overheating. I know of absolutely no circumsatnce wherein it would be appropriate to CHILL an interior windshield surface. Only God knows why but in a Lexus you can actually activate the defrost/defog/demist mode with the system blowing COLD air to it. Most manufacturers have the good sense to HEAT the airflow to the windshield in that mode. Lexus does have a CAUTION note in the manual advising that the defrost/defog/demist mode should not be used to CHILL the windshield when the weather is hot and humid.

Sure...!

I thought they cured that epoxy resin via UV light......???

"worth its salt..." Give me any, ANY reason, why I would want to CHILL my windshield on a hot day. Keep in mind as you answer that when the Porsche is doing this, automatically CHILLING my windshield, when I actually switch to defrost/defog/demist mode I instantly get HOT airflow to the interior surface of the windshield, just as I should.

MY C4 system, and presumably the Touareg and Cayenne, will automatically begin routing CHILLED airflow out of the defrost/demist/defog windshield ducts, once the cabin atmospheric temperature declines nearly, ~75F, to my setpoint, 71F. I try to always remember to prevent this by manually selecting dash outflow only, or for quick cooldown dash and footwell.

I have a letter right here in hand dated September 11th, 2004 from Rick Podorski, Western Regional Service Manager for PCNA, Porsche Cars North America. It is in response to my enquiry of September 1, 2004 regarding the status of a firmware update fix for the climate control system in my 2001 Porsche C4. The C4's climate control system often ("part of the system's normal operation." R. Podorski) cools the windshield so severely on a hot and humid day, or night, that the exterior surface of the windshield will fog over, sometimes almost instantaneously. I had noticed on a web forum that the VW had issued a firmware update for the Touareg SUV that corrected this very problem. So basically my question was if VW has fixed the touareg climate control then the VW fix will probably be applicable to the Cayenne and maybe my C4. Here is a single sentence from my letter which will indicate just how well we can expect a factory service representative to keep up on these things. "Porsche Cars can appreciate the time you have spent researching this matter with another manufacturer, but these are two different systems that cannot be compared." The VW Touareg and the Porsche Cayenne climate control systems CANNOT BE COMPARED! Hmmm... Maybe someone should inform the workers and/or the buyers in the jointly owned Porsche/VW factory where both are build using 90% of the same components. Just as asian manufacturers primarily use NipponDenso, many european manufacturers use Bosch as a resource for electrical and electronic designs. I verified just last evening that an owner of a new BMW has exactly the same complaint. His solution is to lay a towel over the windshield airflow outlet ducts in the summertime to prevent the windshield outside temperature from declining to dewpoint.

I have a letter right here in hand dated September 11th, 2004 from Rick Podorski, Western Regional Service Manager for PCNA, Porsche Cars North America. It is in response to my enquiry of September 1, 2004 regarding the status of a firmware update fix for the climate control system in my 2001 Porsche C4. The C4's climate control system often ("part of the system's normal operation." R. Podorski) cools the windshield so severely on a hot and humid day, or night, that the exterior surface of the windshield will fog over, sometimes almost instantaneously. I had noticed on a web forum that the VW had issued a firmware update for the Touareg SUV that corrected this very problem. So basically my question was if VW has fixed the touareg climate control then the VW fix will probably be applicable to the Cayenne and maybe my C4. Here is a single sentence from my letter which will indicate just how well we can expect a factory service representative to keep up on these things. "Porsche Cars can appreciate the time you have spent researching this matter with another manufacturer, but these are two different systems that cannot be compared." The VW Touareg and the Porsche Cayenne climate control systems CANNOT BE COMPARED! Hmmm... Maybe someone should inform the workers and/or the buyers in the jopintly owned Porsche/VW factory where both are build using 90% of the same components. Just as asian manufacturers primarily use NipponDenso, many european manufacturers use Bosch as a resource for electrical and electronic designs. I verified just last evening that an owner of a new BMW has exactly the same complaint. His solution is to lay a towel over the windshield airflow outlet ducts in the summertime to prevent the windshield outside temperature from declining to dewpoint.

Some manufacturers, Lexus, Toyota and mazda for sure, are adding a porus nylon coating to the vane surfaces into which is embedded a chemical fungicide. Lexus started doing this back in 92 but then apparently had to stop for a few years due to not having filed a MSDS document with the US defining the safe use of the chemical. The pollen filter was added to help matters in this regard, no food (airborne debris) for these microbes, and now I see the LS430 is equipped with a UV light source within the A/C plenum to surppress the microbe growth. The other problem that occurrs with the porus nylon was that once the chemical was leached out due to continuous daily condensate "washings" the evaporator vanes surfaces really did become a GIANT sponge.