Oil Cooler Fan Operation & Troubleshooting
Contributed by Randall
Known to be—or Previously—Operating Incorrectly
Fan Resistor Replacement DIY
Whenever “??” appears, it means that the information is unknown, in question,
or was not clear as provided.
Relay: Inside fuse box in (front)
trunk. Relay is the same as that used for the A/C blower motor and
the rear heater blower. Part #811 951 253. Approximately $28
from a “discount” Porsche dealer. Roy Eames reports the relay is
“generic,” and can be purchased from Pelican Parts for $15.80.
Oil cooler and fan: In right front (passenger
side) fender, behind mud guard. Note that with a flashlight, you
can see the cooler/fan by looking through the horizontal grill at the right-front
corner of the car. You will have to lie on the ground and look up
to do this. A new oil cooler fan (a.k.a. blower) costs approximately
Oil cooler temperature sensor (a.k.a. thermosender,
thermoresistor or thermistor): Behind passenger-side mudguard—or
behind the passenger side headlight on a 993—on the top outer-most part
of the oil cooler unit. Part #964 624 110 00. Approximately
2-speed or ballast resistor: Behind
the oil cooler, mounted to the sheet metal. 0.45 Ohm resistor.
PITA to replace. Part #993 616 521 01. Approximately $45.
Climate control unit: Mounted in dash.
# varies by year & model Around $100 on Ebay (depends
on how lucky you get), around $250-$450 used parts dealer, $900 new.
A reference photo of the oil temperature
gauge, with the white lines given a corresponding temperature, can be found
here (credit to Robin Sun and Viken):
(per Bruce Anderson's hi-performance book) for a 964, 83c/181F
for a 993 (per manual), the oil cooler thermostat opens and oil starts
to flow to the cooler.
At 212For 230F
(993), the thermosender—via the control unit—starts the oil
cooler fan in slow speed.
(964), the oil cooler fan switches to fast speed. The
993’s fast-speed set-point is unknown.
To verify that the oil cooler thermostat
is passing oil to the cooler, simply feel the right-front fender (or wing)
after the engine is warmed up. The fender should be noticeably warm
to the touch. You may also hear a "gurgling" sound coming from the
right-front fender, as oil flows through the cooler.
To verify your fan
is operating with the engine at operating temperature (or warmer):
-Place your hand under
the horizontal grill at the right-front corner of the car and feel for
-As a reference, you
can run your A/C, and check for airflow out of the horizontal grill on
the left-front corner of the car.
Rough (faxed and subsequently
scanned) wiring schematics:
in the picture for a larger view)
Oil Cooler Schematic1
Oil Cooler Schematic 2
Oil Cooler Schematic 3
Oil Cooler Schematic 4
Before going further, you’ll want to check
the 30A oil cooler blower fuse in the luggage compartment fuse box.
To verify that the fan will physically
operate in slow or fast speed:
Keep in mind the relay terminals are energized (12V).
-Remove relay R04 (oil cooler blower).
-Jump terminals 3(30) and 7(87c) for slow
speed. Fan should run, even with the ignition off. If the fan
runs in slow speed, your ballast resistor should be okay.
-Jump terminals 3(30) and 5(87) for fast
speed. Fan should run, even with the ignition off.
You can check the A/C condenser fan similarly,
removing relay R14.
To force the fan to run in fast speed
when the ignition is on:
--On a 993, remove the passenger side headlight,
and unplug the cable shown here (credit to E.J.):
--On a 964, the mudguard must be removed,
and the cable above the fan unit unplugged. The connector looks just
as it does for a 993. After unplugging the cable, you'll probably
need to secure the cable with a tie-wrap--lest it fall into the fan's operating
space (could be messy!).
A photo of the 964 temperature sensor and
oil cooler fan can be found here:
And here is the temperature sensor unplugged,
and the cable tie-wrapped:
-After starting the engine, the fan may
not start running in fast speed until the engine has been running for a
minute or so.
If your A/C blower is operating, you can
perform a "rough-check" of the oil cooler fan relay by swapping the two
identical relays. If your A/C blower no longer operates, it's safe
to say your relay is bad.
Resistance readings for the thermosender.
With the exception of the room temperature reading, all readings are taken
across G12 & G18. G12 & G18 can be accessed from the back
of the climate control unit.
Control Unit Removal
need four, skinny objects to unlock the CCU—unless you happen to have the
special tool. This tool can be purchased at Kragens, Pep Boys, or
equivalent, about $5.
If you don’t have the special tool, some custom tools used in the past
include thin allen wrenches and “tweeker” screwdrivers from a tweeker screwdriver
Your tool of choice gets inserted in the holes in each corner of the CCU.
You’ll want to push the CCU out from behind the dash (lesson learned!).
You may damage the plastic face or pull out buttons if you pull from the
Once you have unlocked the CCU, push the CCU out from behind the dash and
through the turn-signal & cruise control stalks.
Once the CCU is pulled out, you may want to put a rag beneath the unit
to keep it from scratching the dash as you work off the connectors.
Removing the two connectors (“G” & “K”) is a PITA, but self-explanatory.
The connectors are labeled on the back of the CCU, as are the pins.
When taking continuity readings, you may find that you have to press firmly
against the “G” connector pins, lest you get a false open reading.
Or, the equivalent readings can be obtained
at 14-pin connector T-34 in the luggage compartment, between pins #1 and
#10. T-34 is almost directly below one of the screws holding the
long, rectangular shaped plastic cover in place, between the fuse box and
firewall, on the passenger side. In particular, the connector is
visible with the rectangular cover in place, but you may not have enough
space to obtain resistance readings with the cover in place.
If you take readings across connector T-34,
you’ll want to take the readings from the upper (female) part of the connector.
Readings taken across the male portion—with the CCU still connected—will
measure resistance of the CCU (not what you want).
-13.6-19.6 K Ohm
when at room temperature, sensor removed from system (will vary widely
with room temp.).
-3.6-4.0 K Ohm
at 60C (sensor installed, across G12 & G18).
-1.4-1.6 K Ohm
at 85C (sensor installed, across G12 & G18).
-0.9-1.0 K Ohm
at 100C (sensor installed, across G12 & G18).
Expected behavior for a normally operating
-Oil cooler thermostat opens at about the
first mark past warm-up (at approximately 188F).
-At approximately the 9:00
position (probably a little bit above the 9:00
position), the fan will start in slow-speed, corresponding to approximately
(964) or 230F (993). This pic shows a typical start
-Very little information on when the fan
switches to fast speed, but the manual specifies 239F
(964 only, 993 unknown).
-This pic shows a typical temperature
at which the fan (having cooled the oil) shuts itself off:
Varies from car to car, but 122F
- 194F when running on the freeway is normal. As is
reaching the 9:00 position or a bit higher when stuck in traffic on a warm
day. Reading at the 10:00 (248F??)
position is not unusual when tracking a car.
Owners that have just restored automatic
oil cooler fan operation have reported that their engine does not runner
hotter or much hotter than the 9:00 position, even when stuck in stop-and-go
It is safe to assume that routinely running
at the 10:00 or 248F
position is abnormal, as is running above the 248F
mark under any circumstances.
In summary, “by the book,” an engine should
probably run no hotter than the 194F
mark during freeway driving, and no higher than the slow-speed fan starting
temperature when stuck in traffic.
NOTE: R.G. & Sean S. have demonstrated
that—when stuck in traffic—their cars went from running halfway between
the 9:00 and the 248F
position with the fan OOS, to not getting any warmer than the 194F
mark with the fan locked into fast-speed.
-Relay: Self-explanatory, located inside
the luggage compartment fuse-box.
-Climate Control Unit
-Oil Cooler Temperature
-Oil Cooler Fan
Resistor Replacement(for a 993)
AC condenser resistor
And some informative Rennlist threads,
with respect to resistor replacement:
Known to be—or Previously—Operating Incorrectly:
-Roy Eames had a problem with his fan's
operation. Basically, he thought his engine was running too warm
at times (e.g., when stuck in traffic). It's likely his fan wasn't
running at all, and he was getting cooling purely from flow through the
-E.J.'s 993 has a fan that will not operate
automatically. He unplugs the oil temperature sensor (forcing
fast-speed fan operation) when running on the track. His fan runs
both in slow and fast-speed when jumpered.
-Patrick's 993 has a fan that will not
operate in slow speed. The fan runs fine in fast speed, but not in
slow-speed when jumpered.
-R.G.'s '91 C2 fan will not operate automatically
in any speed. Both speeds operate when jumpered, and the fan runs
in fast speed when the oil cooler temperature sensor is unplugged.
R.G.'s car runs no hotter than halfway between the 9:00 position and the
mark (no fan operation). R.G. suspects his fan has been O.O.S. for
a long time, and is getting cooling purely from flow through the cooler.
He knows he is getting flow through the cooler, because he can hear a gurgling
sound, and the right-front fender gets very warm.
Another R.G. observation. With the
oil cooler fan locked into fast speed, the engine’s temperature barely
goes above the 194F mark—runs much
cooler than it did with no fan operation. Sequence of operation with
the oil cooler fan locked in fast speed:
a) Engine warms to 194F,
b) Engine temperature drops quickly to
between the 122F and 194F
mark and remains there—even in stop and go traffic.
-Sean S.’s 993 was running hot when first
purchased, and the problem was corrected by replacing the thermostat.
About 4 months later, he noticed his engine running hot again—averaging
between the 9:00 and 10:00 positions. He found his oil cooler fan
was not running at all.
Sean also observed that with the oil cooler
fan locked in fast-speed (oil temperature sensor disconnected), engine
temperature did not climb above 194F.
-Jai’s ‘95 993 had a slow-seed fan that
would not operate. He has verified that the 2-speed resistor is faulty
through the relay jumper test.
Interestingly, Jai’s A/C condenser fan
2-speed resistor was also faulty, and was replaced by the dealer.
The dealer verified the resistor was faulty using the relay jumper test.
-Even more interesting, Larry N. has a
’95 with the exact same problem as Jai. His car will be going into
the shop soon for resistor (x2) replacement.
-MikeF’s ’94 had an oil cooler fan that
would not operate automatically, and an A/C condenser fan that would cycle
on and off in fast-speed. He verified his A/C condenser resistor
as faulty by the relay jumper test and resistance readings. His oil
cooler fan seemed to check out okay, but still would not operate automatically.
-Multiple cases of failed resistors—too
many to name.
-After troubleshooting, E.J.’s problem
is likely the $CCU$. This has not been verified by use of a donor
CCU. In the interim, E.J. has installed a slow-speed jumper (see
below), which runs his fan continuously in slow-speed.
-Roy Eames' fan works great now.
He replaced the temperature sensor and relay at the same time, so it's
not possible to tell which was at fault. However, based on the resistance
readings Roy took on his old temperature sensor, he suspects the relay
was at fault. Roy’s fan starts in slow-speed at » the 9:00
-R.G. traced his problem to a defective
CCU. The CCU being defective was verified by temporarily installing
a substitute CCU (which started the fan automatically). Considering
the high-cost of a replacement CCU—and the advantages of cooler oil temperatures—R.G.
designed a jumper which runs the fan continuously in slow-speed.
This keeps the oil temperature <194F:
After running with the slow-speed jumper installed
for a few months, R.G replaced his $CCU$, restoring automatic operation
of the oil cooler fan.
-Sean S. learned his relay was defective
by swapping the A/C and oil cooler blower relays. After swapping,
the oil cooler fan worked, the A/C condenser blower did not. Even
though Sean has found the problem, he has elected to run with the temperature
sensor disconnected (i.e., continuous fast-speed operation).
-After replacing the resistor, Jai’s fan
now works automatically in slow-speed. The fan starts at just below
the 9:00 position, and his engine doesn’t run any hotter than the 9:00
position—even when stuck in traffic.
-Larry N. had both the A/C condenser and
oil cooler fan resistors replaced. His car now runs much cooler.
He took resistance readings on the old resistors, and found one reading
about 700 ohms, the other around 7k ohms.
-MikeF. replaced the A/C condenser fan
resistor himself, finding it in horrible shape—nearly 1/3 crumbled away.
Resistor replacement restored normal operation of the A/C condenser fan—i.e.,
operating with the A/C with the ignition on.
Replacing the temperature sensor restored
automatic oil cooler fan operation. Mike’s fan now starts just above
the 9:00 position.
The slow-speed fan jumper test already
verifies the resistor is intact, but an additional check is to measure
resistance across the resistor:
· Measure resistance across terminals
#5 & #7 of the relay plug. Values obtained to date are 0.8
ohms, 0.7 ohms and 0.6
ohms. This applies to both the oil cooler and A/C condenser
fans. Of course, an open circuit indicates a failed resistor.
Yet another verification that the resistor
· Remove the relay, measure voltage
between terminals #2 & #5. Should read around 12V.
· Jumper the fan in slow-speed
(across terminals #3 & #7).
· Measure voltage across terminals
#2 & #5 again. The reading should have dropped to around
4.2V …. the voltage drop across the resistor.
More continuity tests, to verify your
wiring is 100% okay:
· From CCU G-12 to temp. sensor
terminal #2 = continuity.
· From CCU G-18 to temp. sensor
terminal #1, continuity.
· Temp sensor installed, between
G-12 & G-18 = some value depending on hot warm the temperature sensor
· Between K/22 & oil cooler
relay terminal #1 (fast-speed control), continuity.
· Between K/10 & oil cooler
relay terminal #6 (slow-speed control), continuity.
· Between G/9 (voltage feedback)
and oil cooler relay terminal #5, continuity (you may not have the voltage
feedback on a 993).
· Between K/23 & A/C condenser
terminal #6 (slow-speed control), continuity.
· Between G-7 (voltage feedback)
& A/C condenser terminal #5, continuity (you may not have the voltage
feedback on a 993).
How the relay appears to work:
· Terminal 1 = CCU control for oil
cooler blower fast-speed-at 12V when fan is
off, »0.86V when fan is on.
· Terminal 1 = 3-Level pressure
switch control for A/C condenser fast-speed-at 12V
when fan is off, »0.86V when fan is
· Terminal 2 = Always "Hot" (12V)
supply for slow-speed fan. Shorted to terminal 3.
· Terminal 3 = Always "Hot" (12V)
supply for fast-speed fan.
· Terminal 4 = Not used.
· Terminal 5 = 12V,
relayed power for fast-speed fan—not powered when fan is off
· Terminal 6 = CCU control for
slow-speed fan—at 12V when fan is off, »0.86V
when fan is on
· Terminal 7 = 12V,
relayed power for slow-speed fan—not powered when fan is off
· Terminal 8 = Only "Hot"
with accessory position, relay control power??
· There is a 75
ohm resistor between 86 (terminal #8) and 85 (terminal #1) of the
· There is also a 75
ohm resistor between 86 and 85c (terminal #6)
To operate slow-speed fan:
· CCU shorts terminal 6 through
a diode??, which gives the »0.86V.
(The 0.86V is verified. The existence
of a diode within the CCU is not.)
· Relay no longer sees 12V
at terminal #6, closes contact for slow-speed fan.
· Terminal #7 now powered through
terminal #2 (12V), fan starts in slow-speed.
To operate fast-speed fan:
· CCU (or 3-Level pressure switch
for the A/C condenser fan) shorts terminal #1 through a diode (which gives
· Relay no longer sees 12V at terminal
#1, closes contact for fast-speed fan.
· Terminal #5 now powered through
terminal #3 (12V), fan starts in fast-speed.
The current through terminal #8—when the
fan is running—is approximately 12V/75 ohms = » 0.15A.
temperature sensor replacement:
· On a 964, you’ll
certainly have to remove the passenger-side mudguard. You’ll probably
have to do this for a 993, as well.
· You’ll probably
want to perform the replacement when the engine is cool (the thermostat
· Your new sensor
should come with a fresh metal gasket.
· Your Porsche
toolkit includes the correct sized wrench to fit the sensor.
· Expect a small
amount of oil after the sensor is removed. Nothing a few paper towels
· The sensor simply
threads out and in.
· After replacing,
check for oil leaks after the thermostat has opened.
Cooler Fan Resistor Replacement
SUBJECT: Oil Cooler
Date:Thu, 11 Oct 2001
From: "Choi, Jai (JHCH)"
To: "'Randall Granaas'"
Hi Randall, how have you
been ? .....thought that I gave you an update on my oil cooler fan resistor
situation.....well, let's see...where do I start ..
I spent last 2 days (at
least a couple of hours after work) try to replace the darn thing on my
own......finally gave up and took it to my Porsche mechanic at the dealership
this morning. He did exactly what I did as I watched him (no other dealerships
that I know would allow their customers watch mechanics work on cars except
this one....don't ask me why....no complaints from me !!) working on it,
basically loosen up all the bolts that the cooler's attached to the body
of the car. The cooler still wouldn't move and could see from his face
expression that he was running out of patience......well to make the long
story short, I learned a trick today that may help you guys a lot if you
plan to do this on your own.....it basically boils down to one bolt (located
at not so obviously place that is at least to me) that has be removed.
YOU HAVE TO REMOVE THE
HEADLIGHT ASSEMBLY FIRST. UNDERNEATH IT, YOU WILL SEE A BOLT THAT HOLDS
THE SHEET METAL (which is attached to the cooler) IN PLACE......once he
removed it, he was able to slide out the cooler w/ no effort. From
that point on, all you need is a 4 mm allan wrench to take out the old
resistor and put the new one back in place.....maybe 2 minutes job.
Now the fan comes on at
the low speed. It started coming on when the temp needle was approaching
9 o'clock position. As I were driving the car to home even in heavy traffic,
it never exceeded 9 o'clock position. Although I am $150 out of pocket,
I am happy to know that my car has no mechanical flaws now. I am
also happy that I can share this w/ the fellow rennlisters.
Let's keep in touch.
> -----Original Message-----
> From: Randall Granaas
> Sent: Monday, October
08, 2001 10:52 AM
> To: Choi,
Re: oil cooler
> Hi Jai,
> This sounds encouraging.
I have forwarded this information onto E.J. and Patrick (both own '95 993s).
> Look forward to hearing
how your resistor replacement goes. If it was even close to a reasonable
driving distance, I would be more than happy to come over and give you
a hand. I'm in Dana Point, just south of Laguna Beach.
> Good luck with the resistor
> "Choi, Jai (JHCH)" wrote:
> > Hi randall, just talked
to Pete at Andial. He mentioned that no oil cooler lines have to come out.
He said all I have to do is to loosen up the 10 mm bolts (2) holding the
cooler in place on a mounting bracket....the rest is self explanatory (he
> I think I will give
it a shot this evening again.
> > P.S. yes, I live in
Southern California (Bakersfield)....how about you ?
Ballast Resistor Replacement
Date: Thu, 27 Dec 2001 19:37:24
From: "Mike Feinstein"
To: "Randall Granaas"
Thanks again for all your
help with diagnosis, and encouragement with the repair. As you know,
my oil cooler sending unit was the culprit and a new one solved that problem.
Also, thanks to your directions for diagnosing fan problems, I was able
to pinpoint the A/C ballast resistor as the problem in the other front
fender. Besides having no low speed fan when using a jumper as you
describe, when the AC system was turned on, the high speed fan would cycle
on and off at 15 to 20 second increments...also a tell-tale sign that the
ballast resistor is gone. Pulling the fender liner of my 94 964 confirmed
this diagnosis. The old ballast resistor was literally missing a
third of the ceramic material that holds it together. It is suspicious
that the batter overflow tube is located directly above the resistor.
This explains alot. I'm amazed that Porsche would design it this
First thing I did was
add a length of plastic tubing and attach it to the "spigot" that protudes
through the inner fender wall to drain any battery overflow to the ground.
Be sure to tie wrap the tube to ensure no interference with fan operation.
Under normal circumstances,
the resistor is easy to reach and remove...there is an allen screw that
attaches the resistor to the top of the condensor shroud and it threads
into a nut that is welded in place on the inside (unreachable) of the shroud.
The allen screw uses a 4mm allen wrench. Unfortunately, the allen
screw on mine was rusted solid and the head broke off when I attempted
to unscrew it, leaving a permanent stud mounted to the top of my condensor
shroud. I suspect that a bit of battery acid overflow caused this
corrosion and ate my resistor at the same time. Suspisciously though,
there is no other evidence of battery acid leakage...strange.
I started the car and
turned on the AC with the new resistor plugged in, but unmounted....the
AC fan came on low speed and stayed that way.......a beautiful thing.
I agonized for some time about a suitable location to mount the new resistor.
Since the resistor wire is fairly short, I decided to mount it to the inside
fender wall, just above its original location (see pics). To do this,
I had to drill a small hole in the fender wall to accomodate a single 6mmx30mm
stainless hex head bolt. I placed a lock nut in the hex opening in
the resistor (it was clearly made for this) fastened it in place
with only the screw head and a washer showing under the front carpeting
against the fender liner. Be careful not to over tighten the resistor
because it appears to be made of a ceramic type of material and seems like
it could break with too much torque on the screw. I snugged it up
until I could no longer rotate the resistor by hand.
Although I removed the
mudguard and the lower plastic fan cover, only the mudguard was necessary
for this repair. The finished product looks clean and professional.
I suspect that the only reason the resistor comes mounted on the condensor
shroud from the factory is that it made it easier to install the fan/condensor
as one complete unit with a minimum of external connections. The
new resistor is well away from the newly extended battery overflow and
if the resistor ever dies again, replacing it will take 10 minutes, tops.
Thanks again for all your
help Randall. You saved me a bundle and I had fun doing the repair.
Just wish I had access to a hammer to clear the old fault codes.
Original Relay Position
Battery Drain with
New Resistor Mounted
in New Location
Old and New Resistors
information were obtained from Randall's web site, click here to visit
his web site
DIY is contributed by Dan 96C2 St.Louis
(Posted on Rennlist
Discussion board 7/22/02)
Fan Resistor Replacement
By following the diagnostic steps from
p-car.com, I determined that both my AC condenser & oil cooler fan
series resistors were defective.
I planned to replace both today, but due
to unexpected complications & 100F temps only did the AC side. The
job is technically easy (maybe a 3 on a 10 pt scale), but the location
of the resistor makes it a frustrating, cursing, sweaty, pita project.
It is not necessary to remove the bumper
to get to the AC resistor & unless the Turbo nose & front end internals
are far different than my Carrera, it wouldn't help anyway. It is only
necessary to remove the front most fender liner.
- #2 phillips screwdriver.
- 4mm hex wrench (a 1/4 inch drive fine
tooth ratchet wrench w/4mm shortened shank hex socket makes this project
much easier - see below).
- very small hands with very long fingers.
- infinite patience.
The steps are:
1. Jack up the front end, secure w/jack
stand & remove the wheel.
2. Remove the front section of the fender
liner - rather intuitive after removing 7 or so screws.
3. Disconnect the resistor plug electrical
connection (just pulls apart) after pulling the connector from the plastic
clips on the inside fender wall.
4. The resistor is located at the top
of the interior side of the condenser/cooler. It is secured with one (1)
4mm hex head (internal - "allen") screw through the center of the resistor.
5. Now comes the pita part:
A. the screw is not visible & must
be removed & re-installed by feel - it's difficult to get the hex wrench
mated to the screw,
B. the space is so limited that my avg
size hand could barely fit, precluding turning the screw by hand,
C. the arc for turning a fixed hex wrench
or a ratchet w/hex socket is, perhaps, 20-30 degrees, so it takes many
partial turns (wish I had a fine tooth ratchet), and
D. the clearance above the screw head
is insufficient to fit the tools I had. I ended up using a 1/4" ratchet
wrench w/4mm socket & a very short piece of 4mm hex wrench cut to size
w/a Dremel (or use a hack saw) & temporarily glued into the socket
w/just 1/8" exposed.
6. Removal takes time, but once I made
the tool, wasn't too bad.
7. Re-installation of the new resistor
is the reverse of the above, but since the screw hole is not visible &
the screw has a fine thread, it took me many, many, many tries during which
I had nothing good to say about our marque. The only good thing is there's
no place for a dropped socket to go.
Perhaps someone has an easier way I overlooked
to get to the AC resistor. It looked to me that the only alternative is
to drop the AC fan/condenser which seemed at least as much trouble.