964/993 Oil Cooler Fan Operation & Troubleshooting
Contributed by Randall Granaars
Stuff You'll Find:
Component Location/Part Number/Cost
NOTE: 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 $100.
Oil cooler temperature sensor (a.k.a. thermosender, thermoresister 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 $16.
2-speed or ballast resister: Behind the oil cooler, mounted to the sheet metal. 0.45 Ohm resister. PITA to replace. Part #993 616 521 01. Approximately $45.
Climate control unit: Mounted in dash. Part
#?? 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):
At 87c/188F (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 212F, the
thermosender via the control unit starts the oil cooler fan in slow speed.
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 air.
Rough (faxed and subsequently
scanned) wiring schematics:
Before going further, you will want to
check the 30A oil cooler blower fuse in the luggage compartment fuse box.
Caution: Keep in mind
the relay terminals are energized (12V).
You can check the A/C condenser fan similarly, removing
--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.
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 will 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.).
Some expected behavior for a normally operating system:
-Oil cooler thermostat opens at about the first mark past
warm-up (at approximately 188F).
Varies from car to car, but 122F - 194F when running on the freeway is normal. As is reaching the 9:00 position or halfway between 9:00 and the 248F position when stuck in traffic on a warm day. Reading at the 10:00 (248F??) position is not unusual when tracking a car.
A disclaimer with respect to the above paragraph. It's possible that reports of normal operation halfway between the 9:00 and the 248F positions may actually have been given by owners that are not aware their oil cooler fan is O.O.S. 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.
Owners that have just restored automatic oil cooler fan operation have reported that their engine does not runner hotter than the 9:00 position, even when stuck in stop-and-go traffic.
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.
-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 oil cooler.
-E.J.'s 993 has a fan that will not operate in fast speed 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 248F 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, thermostat opens.
-Sean 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 resister is faulty through the relay jumper test.
Interestingly, Jai's A/C condenser fan 2-speed resister was also faulty, and was replaced by the dealer. The dealer verified the resister 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 resister (x2) replacement.
-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 Ã» the 9:00 position .
-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 resister, 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.
-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:
The slow-speed fan jumper test already verifies the resister is intact, but an additional check is to measure resistance across the resister:
Yet another verification that the resister is intact:
More continuity tests, to verify your wiring is 100% okay:
How the relay appears to work:
To operate slow-speed fan:
To operate fast-speed fan:
The current through terminal #8 when the fan is running approximately 12V/75 ohms = » 0.15A.
Pelican Technical Article:
964/993 Oil Cooler Fan Operation & Troubleshooting
Porsche 964 Carrera 2 (1990-94)
General knowledge and troubleshooting on your oil cooler fan operation.