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Back to Over heating Again!!

Decided that today was a good day to go for a drive and test the cooling system as its about 100 deg F out today!! Got about half way through Topanga Canyon and actually got so hot the red light came on. Parked in shade opened the hood and only the slow speed fans were on. It's easy to tell if the high speed ones come on as it sounds like somethings going to fly out of the engine compartment. Temp went down to just below the top white line. Drove home slowly without light coming on. Got out of car in the driveway and then the high speed fans came on. Temp went down pretty quickly to about half way on the stock gauge. Turned off engine and the slow speed fans stayed on. Tested fans by turning the ign to ON and the high speed fans came back on. I'm thinking that the high speed fans are coming on intermittently instead of when they should be. Oh yeah also tried turning on and off the AC but the high speed fans never came on!!

1) Bad Ground?
2) Stupid thermo switch?
3) Stupid fan resistors?
4) Stupid Driver?

Mike G.


Last edited by Mike Goebel; 08-01-2020 at 11:04 AM..
Old 08-01-2020, 10:48 AM
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When you tee it up like this....boy hard to resist, but I will.
My vote is on the the coolant thrmo switchs. 1 trips at 92 the other at 102.
If not them then the control relay it self G10.
Sox
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Old 08-01-2020, 01:52 PM
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Quote:
Originally Posted by soxnail View Post
My vote is on the the coolant thrmo switchs. 1 trips at 92 the other at 102.
Sox
Can these types of mystical electronic devises fail resulting in intermittent functioning?

Took off the relay cover. Thing looks brand new on the inside. Used a magnifier and didn't see anything that looked strange. Does this relay control the high speed fans coming on when the AC is turned on? Because the HS fans didn't come on after turning on the AC when car was running in the driveway after the drive. But then for some reason the HS fans came on later with the AC off.

Mike G.

Last edited by Mike Goebel; 08-01-2020 at 04:14 PM..
Old 08-01-2020, 03:30 PM
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The relay G10 also controls the fans for AC operation.
The temperature switch is 944 616 513 00.
I need to chase the sequence more, but the fans should cut on with AC on.
You are going to have to use a meter to trouble shoot..
I will write up a quick procedure to do so and post, but a meter is going to be a must. You will also need a thermometer of some type to monitor the coolant temp.
Sox
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Old 08-01-2020, 05:15 PM
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Sorry and yes the temp switches can fail in intermittent connection mode.
Sox
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Old 08-01-2020, 05:16 PM
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More reading....
-Ac on only turns on slow speed fans.
-Fast fan speed will not happen without ignition on.
-Fast fan is controlled by the high temperature thermo switch only.
-Resistor pack issues will cause slow speed issues, will have no effect on high fan speed.
Sox
And yes before you ask insomnia is my friend.
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Old 08-01-2020, 09:50 PM
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Originally Posted by soxnail View Post
-Fast fan is controlled by the high temperature thermo switch only.

And yes before you ask insomnia is my friend.
This makes me believe its the thermo switch! I was up too finishing my last beer.

Mike G.
Old 08-02-2020, 09:13 AM
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I haven't followed your thread on overheating, but did you ever change the thermostat?

A stuck thermostat would certainly cause overheating, and restricting the flow of hot coolant to the radiator would keep the thermoswitch from turning on the high speed fans.

Not easy to remove, but, once out of the waterpump, easy to test (pan of hot water at opening temperature, look for wide opening).
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Old 08-02-2020, 10:13 AM
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Guess I should add that everything in the cooling system is new except for the Rad and anything electronic.

Mike G.
Old 08-02-2020, 10:37 AM
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Quote:
Originally Posted by Mike Goebel View Post
Guess I should add that everything in the cooling system is new except for the Rad and anything electronic.

Mike G.
Well, if that's the case, never mind.
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Good luck, George Beuselinck
www.944ecology.com
Porsche Deconstructor (tm)
We buy 944s and sell 944 parts (845-379-1944)
We rebuild torque tubes and instrument clusters for 944/968/928
Old 08-02-2020, 11:13 AM
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Mike you round up a meter and a thermometer ?
Sox
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Old 08-02-2020, 01:45 PM
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You don't want to go digging after the thermo switches till you eliminate the other stuff. It is a PITA to get to.
Have to drain the cooling system, remove hoses up by the radiator and then you get to the switch. The relay is a likely suspect so needs to be eliminated first.
Sox
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Old 08-03-2020, 06:52 AM
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Quote:
Originally Posted by soxnail View Post
Mike you round up a meter and a thermometer ?
Sox
Yeah I got those. No power supply but I do have a battery charger.
Quote:
Originally Posted by soxnail View Post
The relay is a likely suspect so needs to be eliminated first.
But you listed this: "Fast fan is controlled by the high temperature thermo switch only."
My Fast fan did not come on when the temp was very HOT!


Mike G.

Last edited by Mike Goebel; 08-03-2020 at 07:31 AM..
Old 08-03-2020, 07:27 AM
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Yup bad wording the Hi temp thermo switch runs a part of the relay which then runs the fan at high speed.
Sox
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Old 08-03-2020, 10:52 AM
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Testing the G10 (AC/cooling fans) relay:
Stuff needed:
-12v source, can use the battery but not recommended. You can use a battery charger if it has a constant 12V output. Cannot use a ‘pulse’ style charger.
-Multiple leads with alligator clips on both ends. See pic below.
-Something to simulate the fan motors, use a 12v bulb in a socket with leads or solder some leads to a bulb. See pic.
- A meter is nice to have but not essential.
Testing the G10 (AC/cooling fans) relay:
Stuff needed:
-12v source, can use the battery but not recommended. You can use a battery charger if it has a constant 12V output. Cannot use a ‘pulse’ style charger.
-Multiple leads with alligator clips on both ends. See pic below.
-Something to simulate the fan motors, use a 12v bulb in a socket with leads or solder some leads to a bulb. See pic.
- A meter is nice to have but not essential.
Refer to the attached diagram.
-Connect 30M1 and 30M2 to a 12v source +.
-Connect the 12v source – to 31.
First, we are going to test the M1/M2 relay which runs the high-speed fans output.
-Connect light bulb to M1 and 31.
-Connect TF to 31.
-Connect to either 30M1 or 30M2 with one end of the clip lead.
- Momentarily touch the other end of the lead (one connected to 30M1/30M2) to X.
- Relay will click and bulb will come on. If so of M (M1) is working.
-Connect light bulb to M2 and 31.
- Momentarily touch the other end of the lead (one connected to 30M1/30M2) to X.
- Relay will click and bulb will come on. If so second of M (M2) is working.
Next, we are going to test the TS and V1/V2 relays which runs the slow-speed fans output.
- Disconnect TF to 31.
- Connect light bulb to V1 and 31.
- Connect to 31 with one end of the clip lead.
- Momentarily touch the other end of the lead (one connected to31) to TS.
- Relay will click and bulb will come on. If so of TS/V (V1) is working.
- Connect light bulb to V2 and 31.
- Momentarily touch the other end of the lead (one connected to 31) to TS.
- Relay will click and bulb will come on. If so second of TS/V (V2) is working.
- If neither works then it could be the TS relay or both V1 and V2 are bad.
Next, we are going to test the AC and V1/V2 relays which runs the slow-speed fans output
- Disconnect the end of the clip lead from 31.
- Connect to 30M1/30M2 with one end of the clip lead.
- Momentarily touch the other end of the lead (one connected to 30M1/30M2) to AC.
- Relay will click and bulb will come on. If so AC control to fans is working.
G10 has passed!!





Block functional diagram of the G10.
Sox

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Last edited by soxnail; 08-07-2020 at 12:32 PM.. Reason: Added AC fan test
Old 08-03-2020, 11:04 AM
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Next post on fixing the G10
Sox
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Old 08-03-2020, 11:19 AM
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BTW it is obvious that the G10 relay has been previously opened!!

I had also done this test, a while back, at the bottom of this procedure for the thermo switch and it tested ok.

Cooling Fan Operation and Troubleshooting

Mike G.

Last edited by Mike Goebel; 08-03-2020 at 11:46 AM..
Old 08-03-2020, 11:42 AM
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Ironic, To write the above procedure I pulled my G10 to confirm that the procedure works...
My V2 relay was bad. So for some time only one fan was working at slow fan speed. Since there was fan noise from the second fan and my car's temp never went up, I never realized this.
The high speed fans system still worked.
If ever there was a case of "physician heal thy self"
Any way opened it and took the V2 relay out. Replaced it with a generic 12v I had lying around. Used epoxy to hold the new relay in and ran some wires to connect it. See pics.
Sox





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Old 08-03-2020, 09:15 PM
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So typically when an old style relay goes out is it the coil winding that is broken? I could go back and look a little bit closer.

Mike G.
Old 08-04-2020, 08:48 AM
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Yes most likely, the other thing is the diode in circuit is burnt open.. You can use a meter on them they should conduct in one direction but not in the other.
Sox

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Old 08-04-2020, 09:05 AM
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