C4S Radiator Fans

Now that the weather is heating up, I'm dealing with some overheating issues that weren't noticeable in the cooler months. My C4S really doesn't like to be running if it's not moving. Idling while parked or moving through stop-and-go traffic and the water temperature rises past 190 degrees. The other day it was around 90F outside and I had to pull over to let the engine cool off as the gauge was rapidly climbing above 200 degrees. I was thinking I had a thermostat stuck in the closed position, but the engine stays in the appropriate temp range as long as I'm moving above 40mph. I realized that since I purchased the car a little over a year ago, I've never noticed the front radiator fans running. I attempted to diagnose the issue today and could not get either side to run in low or high speed mode. The relays click when I turn on the AC, but I get nothing from the fans. Since it's not an issue with fuses/wiring/relays, that just leaves the resistors or the fan motors. But would bad resistors prevent the fans from running at either speed? The plan is to swap out both the left and right radiator fans, which include new resistors in the wiring. But it seems that the C4S and Turbo models have a different radiator fan part number than the narrow-body 996 models. I'm hoping that the standard 996 fans (99662413500) will work, since the wide body fans (99662412700) are twice the price. Has anyone done this successfully? Or are they indeed different parts?

Quotes source post: 20040604

How are you diagnosing this? What is your method? Turning the AC on merely activates the low-speed relays, which rely on functioning resistors to activate the fans at low speed. When the high-speed relays are activated, battery power is sent directly to the fans - bypassing the resistors - running them at full speed. How familiar are you with relays, wiring identification, and using a multimeter? If you�re comfortable with this sort of work, you can troubleshoot your problem starting at the relay holder. If not, then you still have a chance of troubleshooting the fans, but you�ll have to remove the wheel and fender liner (maybe both sides). Then you�ll be able to locate the connector for the radiator fans and try to turn them on using battery power and ground. If you have a diagnostic scan tool, you may be able to use it to activate the fans at varying speeds (I don�t know if it�s actually possible for this car - I never tried. But there�s a good chance it�s doable.) Do you have a diagnostic scan tool, and which one do you have? edit: If I had to guess, I�d say the fan resistors are malfunctioning and need to be replaced. They�re pretty expensive for what they are, but they�re probably cheaper than the fans.

The 4S and Turbo probably have the same fans, the Turbo fan resistor must be different because Turbo has 3 speed fans and I have never heard of the Turbo resistor failing. The 2 speed fan resistor seems to fail and is an easy fix.

Option 1 start buying hundreds of $ of parts and and maybe get it right. Option 2 but a $30 multimeter and source the wiring diagram( Bentley manual is very good for this) and do some testing. U can even set up your own Piwis3 system for $75-250 and activate the fans individually. The diagnostic tools r affordable and will continue to save u money. Its a pretty simple system to test. Work your way checking for 12v from the fuse to the fan (also dont forget to check the ground). The fans r the same as the turbo because a c4s uses turbo rads but i do think the resistor is different.

Quotes source post: 20040604

The ^ above ^ quote only means the 'click' of the relay's control circuit has kicked in. Has nothing to do with the high amperage side of the relay. The relay can 'click on but if there is no voltage in the power side of the relay nothing will happen. 2 different circuits with different fuses. Could be a simple fuse blown problem. If so check why fuse blew.... jmo

Narrow body and wide body fans mount differently to the rad bracket. which is also a different bracket along with the air ducking too. I have a turbo/c4s bumper on my c2, I got the air ducking to match but as it mounts differently was unable to fit it.

Quotes source post: 20040604

Before you do anything, monitor the ECTS readings, either with a Durametric, or an ODBII dongle connected to an app on your phone. It�s possible the only problem you have is that you think your temps and high but they are not. My �99�s temp gauge goes ways past 180 all the way to the last white line, where the low speed fans kick on because that�s 96.75C. The dash gauge is not always accurate or precise. You can test fan speed operation with a Durametric as well. I agree, there is a problem with your low speed fans though.

Mine will run with the needle in the middle of the 0 of 180......maybe sometimes slightly past (0) that when stuck in traffic on a hot day.......was told thats normal for temp?

Quotes source post: 20041179

Normal temps range from -30-102C and anything in between. Normal operating temps range from 83C-102C, and anything in between. So it doesn�t matter where the needle sits on the temp gauge if it�s in that temp range, as reported by the DME because the dash gauge isn�t accurate or precise.

I have a Durametric I can hook up and try to trigger the fans at both speeds, but If the resistors are bad, will the fans still actuate?

Quotes source post: 20041369

If the resistors r bad they will not work at slow speed. High speed bypasses the resistor. This only if the fuse/ relay/ wiring is good. If the fan does not turn on for low speed but works for high its the resistor. If the fans dont work at all u need to look at the 12v and ground fan circuits.

So it doesn’t matter where the needle sits on the temp gauge if it’s in that temp range, as reported by the DME because the dash gauge isn’t accurate or precise.[/QUOTE] I recently had mine looked at because I was concerned the car was running hot and the INDY I went to has an actual "Porsche" reader and said my gauge and what they were reading were fairly accurate. So slightly past the "0" on the gauge is 205

you can remove the relays and use a jumper wire to check if they come on, that will at least tell you if the resistors are bad. Refer here: https://rennlist.com/forums/996-foru...acement-2.html

Quotes source post: 20041581

I recently had mine looked at because I was concerned the car was running hot and the INDY I went to has an actual "Porsche" reader and said my gauge and what they were reading were fairly accurate. So slightly past the "0" on the gauge is 205[/QUOTE] Different years have different results. If yours is accurate, that�s great. Slightly past zero, a lot of people get worried, but 205F isn�t anything to worry about.

Both of my actual fans were dead so I replaced them with the standard 996 ( 99662413500) units. The resistors are different but use the same connector plugs, so it's a direct fit. I could probably wire in the old resistors if I cared about keeping the 3-speed fan functionality, but I don't see the need for an intermediate mode on the fans between low and high. The Turbo/C4S fans seem to use different hardware to mount to the fan shroud, though. The old units have larger diameter bolts that are not removable from the fans, while the replacement fans just have (smaller) bolt holes. I had to make a trip to the hardware store since I wasn't able to reuse the original mounting components. I also took the time to clean out the radiators and condensers really well while I had the bumper off, and added a mesh screen to hopefully prevent debris build-up in the future. They were VERY dirty.

Very dirty indeed .. just did a left fan replace and cleaned both sides .. no more over heat .. 99 C4 � 63k miles if your pulling the bumper do both sides..