Cooling fans won't shut off
05-22-2023, 05:53 PM
#1
Instructor
Thread Starter
Cooling fans won't shut off
First real problem with my '87 944 S since I got it. Dead battery this am.
Cooling fans won't shut off - looks like fan 2.
Bad T'stat? Where might I find it.....looking in my Haynes manual - but it does not cover the S models......
TIA,
GN
Cooling fans won't shut off - looks like fan 2.
Bad T'stat? Where might I find it.....looking in my Haynes manual - but it does not cover the S models......
TIA,
GN
05-23-2023, 10:43 AM
#3
Burning Brakes
Join Date: Oct 2021
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Do not use the Haynes manual - it doesnt clearly define the differences between late/early/S/S2/turbo models. Just throw it in the trash. The factory service manuals are available in PDF format for free. Use that.
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
Last edited by walfreyydo; 05-23-2023 at 10:45 AM.
05-23-2023, 03:28 PM
#4
Three Wheelin'
From experience.. could be the fan relay itself… stock ones are really expensive ..
focus 9 is a good choice, they also make one with diagnostics built in.
focus 9 is a good choice, they also make one with diagnostics built in.
The following users liked this post:
boom10ful (05-24-2023)
05-24-2023, 10:37 AM
#5
Instructor
Thread Starter
Ok - removed fuse to Cooling Fan 2 - and all is well. Fan 1 shuts off as it should. As it isn't really hot yet, car does not overheat with only 1 fan running.
Doesn't this eliminate the thermo switch as being the problem?
And where is the relay? Is it in the electrical box with the fuses and other relays?
Just what is it that calls for Fan 2 to activate/energize? Does one relay control both fans?
Thanks!
GN
Doesn't this eliminate the thermo switch as being the problem?
And where is the relay? Is it in the electrical box with the fuses and other relays?
Just what is it that calls for Fan 2 to activate/energize? Does one relay control both fans?
Thanks!
GN
Do not use the Haynes manual - it doesnt clearly define the differences between late/early/S/S2/turbo models. Just throw it in the trash. The factory service manuals are available in PDF format for free. Use that.
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
05-24-2023, 10:40 AM
#6
Instructor
Thread Starter
Trending Topics
05-25-2023, 10:00 AM
#8
Instructor
Thread Starter
Ooops! Forgot to THANK YOU for this great info. I shoulda known Clarks Garage would have it!
GN
GN
Do not use the Haynes manual - it doesnt clearly define the differences between late/early/S/S2/turbo models. Just throw it in the trash. The factory service manuals are available in PDF format for free. Use that.
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
http://p914-6info.net/944%20Manuals.html
Read through clarks (you should bookmark this site, shop manual section).
The main systems for cooling fans are:
-radiator thermo switch (activates relay based on temp, has two voltages for high/low temp)
-fan relay (switches power to fan either high or low speed based on thermo switch)
-fan resistors (controls speed of fans high/low)
-fans
First thing to test is the relay (by bridging the thermo switch plug) and thermo switch (can be tested with multimeter and hot water). The procedure is listed on clarks. If your fans dont turn off, its likely one of those
http://www.clarks-garage.com/shop-manual/cool-01.htm
05-25-2023, 10:05 AM
#9
Instructor
Thread Starter
Hmmm.......appears to me that both fans always run together, but at a low speed (92 deg. on thermo switch) with resistor in circuit, and high speed (102 deg. on thermo switch) w/o the resistors in the circuits.
Is this correct?
If so, strange that only Fan 2 would run by itself, and would seem to point to relay.
If so, also strange that two fans would not be switched together in the relay using just 2 coils instead of 4 - from a design perspective........
But I have not tested thermo switch as per Clark's Garage yet......
Is this correct?
If so, strange that only Fan 2 would run by itself, and would seem to point to relay.
If so, also strange that two fans would not be switched together in the relay using just 2 coils instead of 4 - from a design perspective........
But I have not tested thermo switch as per Clark's Garage yet......
05-25-2023, 02:49 PM
#10
Burning Brakes
Join Date: Oct 2021
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Originally Posted by Clarks Garage
Cooling Fan Operation On Late Model 944s
The cooling fan operation on late model 944s is similar to that of early 944s. However, there are some distinct differences.
The late model 944s use a "slow speed" resistor similar to the early cars. However, on later cars, there are two resistors, one for each of the fan motors.
As with the early cars, the thermofan switch (at 92 °C) will complete the fan circuit, even if the ignition is not on. However, unlike the early cars when the fan circuit is completed, both fans run instead of just the driver's side fan. Also, on the later cars the thermofan switch is a dual element temperature switch with one contact closing at 92 °C for slow speed operation and one closing at 102 °C for high speed operation (slow speed resistor bypassed). The fans will operate is slow speed regardless of ignition switch position. However, fast speed operation is only available with the ignition switch on.
For a late model 944 cooling fan circuit diagram click here
The cooling fan operation on late model 944s is similar to that of early 944s. However, there are some distinct differences.
The late model 944s use a "slow speed" resistor similar to the early cars. However, on later cars, there are two resistors, one for each of the fan motors.
As with the early cars, the thermofan switch (at 92 °C) will complete the fan circuit, even if the ignition is not on. However, unlike the early cars when the fan circuit is completed, both fans run instead of just the driver's side fan. Also, on the later cars the thermofan switch is a dual element temperature switch with one contact closing at 92 °C for slow speed operation and one closing at 102 °C for high speed operation (slow speed resistor bypassed). The fans will operate is slow speed regardless of ignition switch position. However, fast speed operation is only available with the ignition switch on.
For a late model 944 cooling fan circuit diagram click here
If only one fan is running you need to test the wiring/voltage being sent to the bad fan (while the relay is jumpered instead of doing it with the car running/overheating). If no voltage then test the next step in the chain (I think its the resistor). This might require looking at the wiring diagram to see where the wiring to the fan comes from, which can be found here, if you google.
Last edited by walfreyydo; 05-25-2023 at 02:56 PM.
05-25-2023, 05:42 PM
#11
Instructor
Thread Starter
Walfrey - I did read through and thought what I said paralleled both what Clarks said and what the schematic shows - both fans run together in low speed (resistor circuit) and high speed (circuit w/o resistor). I totally get it. Fans on low at 92 C and high at 102 C. I must be mis-communicating.
Fan 2 was not shutting off even after engine was cold, ignition off. I removed fuse to prevent that, carefully monitoring water temp - it never overheated. I put the fuse back in today. Fan 2 not running when it shouldn't.
I will test thermo switch when I have a chance.
Everything now seems to be working properly.
Thanks,
GN
Fan 2 was not shutting off even after engine was cold, ignition off. I removed fuse to prevent that, carefully monitoring water temp - it never overheated. I put the fuse back in today. Fan 2 not running when it shouldn't.
I will test thermo switch when I have a chance.
Everything now seems to be working properly.
Thanks,
GN
Seems like you didnt read through clarks, its pretty clear that on a late model car, both fans operate in slow and high speeds... Please read through clarks as I think you are misunderstanding how the fan cooling system works, whats normal whats not normal. How to test the relay, its all in there. Just put in the time to do the reading and research.
If only one fan is running you need to test the wiring/voltage being sent to the bad fan (while the relay is jumpered instead of doing it with the car running/overheating). If no voltage then test the next step in the chain (I think its the resistor). This might require looking at the wiring diagram to see where the wiring to the fan comes from, which can be found here, if you google.
If only one fan is running you need to test the wiring/voltage being sent to the bad fan (while the relay is jumpered instead of doing it with the car running/overheating). If no voltage then test the next step in the chain (I think its the resistor). This might require looking at the wiring diagram to see where the wiring to the fan comes from, which can be found here, if you google.
05-26-2023, 11:35 AM
#12
Burning Brakes
Join Date: Oct 2021
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Fans run even with ignition off sometimes if coolant temps are high, usually shut off within a few minutes. If not, then you may have an issue with the fan relay.
If you jumper the fan relay (clarks method), do both fans turn on/off (high/low speeds) as normal or do you get only one fan running? Only one fan runs when ignition if off, but acts normally otherwise?
If you jumper the fan relay (clarks method), do both fans turn on/off (high/low speeds) as normal or do you get only one fan running? Only one fan runs when ignition if off, but acts normally otherwise?
Last edited by walfreyydo; 05-26-2023 at 11:40 AM.
06-20-2023, 09:16 AM
#13
Instructor
Thread Starter
New thermo-switch is IN, all is well. Thanks to all.
BOY was that thing a bear to get to! I have relatively small hands and cannot imagine how guys with big hands do it!
GN
BOY was that thing a bear to get to! I have relatively small hands and cannot imagine how guys with big hands do it!
GN
Fans run even with ignition off sometimes if coolant temps are high, usually shut off within a few minutes. If not, then you may have an issue with the fan relay.
If you jumper the fan relay (clarks method), do both fans turn on/off (high/low speeds) as normal or do you get only one fan running? Only one fan runs when ignition if off, but acts normally otherwise?
If you jumper the fan relay (clarks method), do both fans turn on/off (high/low speeds) as normal or do you get only one fan running? Only one fan runs when ignition if off, but acts normally otherwise?