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Cooling fan operation

 
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bureau13  



Joined: 07 Sep 2017
Posts: 69
Location: South Florida

PostPosted: Thu May 03, 2018 1:31 am    Post subject: Cooling fan operation Reply with quote

I've recently started overheating, but only at idle or stop and go traffic. Long open roads at speed, no problem. Sounds like fans, right? Only, I hear them running after I shut the car off, as they usually do.

I found a fan troubleshooting guide on Clark's garage for early 944s...and that indicated that the driver's side fan runs at two speeds, and the passenger side fan depending on AC operation. I have definitely had overheating issues with AC both on and off, although I can't really see the fans that easily so I can't say which is running, or how fast. But first things first...does the 924/931 work that way? Or is that 944 info not applicable here?
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Thu May 03, 2018 5:39 am    Post subject: Reply with quote

Turbo rads are near their limit of efficiency whilst new. Old coolant systems get furred up. Rads get less efficient. When slow or stopped the rad fan (singular) will always come on assuming the rad switch is working as there is no air flow. Fan will operate when needed, not all the time, not always when shutting down, unless the system is not optimal.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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bureau13  



Joined: 07 Sep 2017
Posts: 69
Location: South Florida

PostPosted: Thu May 03, 2018 7:45 am    Post subject: Reply with quote

Hmm...I most definitely have two fans, and I have the cooling fan relay described in the early 944 material.

My working assumption at this point is that my cooling fan relay is bad. I need to test it to make sure, but it makes perfect sense if I assume I have the same configuration as the early 944s, which everything I have seen on my car indicates that I do.

Carrera RSR wrote:
Turbo rads are near their limit of efficiency whilst new. Old coolant systems get furred up. Rads get less efficient. When slow or stopped the rad fan (singular) will always come on assuming the rad switch is working as there is no air flow. Fan will operate when needed, not all the time, not always when shutting down, unless the system is not optimal.

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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924RACR  



Joined: 29 Jul 2001
Posts: 8099
Location: Royal Oak, MI, USA

PostPosted: Thu May 03, 2018 11:25 pm    Post subject: Reply with quote

My temp will definitely shoot up after coming off the highway to stop at a light... often I'll switch the AC on as I'm coming to a stop, in hot weather, just to run the fans early (instead of waiting for the temp spike)...

But a flush of the cooling system might not hurt too. Though yes, first step verify proper power supply to the fans.
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
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bureau13  



Joined: 07 Sep 2017
Posts: 69
Location: South Florida

PostPosted: Sun May 06, 2018 8:14 am    Post subject: Reply with quote

Just to wrap this up and put a bow on it...it was the relay.

Some things I learned (for the dual fan AC-equipped cars):

The driver's side fan runs at slow speed if the temp switch on the radiator is closed. With ignition on, if that switch is closed, it runs at high speed (I think) and if the AC is on, the passenger-side fan runs at high speed. Both fans run if AC is on, regardless of that temp switch.

There are two relays that play a big role here: The AC relay (position 3) and the cooling fan relay (position 1...this one was my problem). I'm not sure what relay is REALLY needed in position 3, since I didn't have to remove that one, but in position 1 you need 944 615 113 00 (or 01 or 02). It has six pins, and closes two switches (one for each fan) when it is triggered. Early 944s use this same relay (and same fan setup in general). There is a lot of stuff on the internet...and possibly factory documentation...that says this should be a 4-pin 53 generic relay. THEY'RE LYING.

Anyway, long story short, a friend of a friend had a dead '83 944, and we pulled the relay from that. No more overheating!
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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1980NC931  



Joined: 15 Jun 2018
Posts: 1
Location: North Carolina

PostPosted: Fri Jun 15, 2018 4:52 pm    Post subject: Reply with quote

yeah i was having issues with my 1980 924 turbo cooling system.

the temperature switch was messed up but once i fixed that it was revealed that the relay was also not right.

I've got the 5 part manual for the car but every option detailed for the relays seemed wrong. relay 1 taking care of A/C AND being a part of the radiator circuit makes the books make sense.

I guess the logic there is that the A/C automatically turns on the radiator fan so they had to wire it in to the circuit somewhere?
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bureau13  



Joined: 07 Sep 2017
Posts: 69
Location: South Florida

PostPosted: Sat Jun 16, 2018 11:31 am    Post subject: Reply with quote

I took some staring and thinking, but once I had the schematic straight it all made sense, more or less. There's a lot of misinformation out there about exactly what relay is needed. In this case, I pulled it from the same location in an early 944, and it was perfect.

1980NC931 wrote:
yeah i was having issues with my 1980 924 turbo cooling system.

the temperature switch was messed up but once i fixed that it was revealed that the relay was also not right.

I've got the 5 part manual for the car but every option detailed for the relays seemed wrong. relay 1 taking care of A/C AND being a part of the radiator circuit makes the books make sense.

I guess the logic there is that the A/C automatically turns on the radiator fan so they had to wire it in to the circuit somewhere?

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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924RACR  



Joined: 29 Jul 2001
Posts: 8099
Location: Royal Oak, MI, USA

PostPosted: Sat Jun 16, 2018 10:45 pm    Post subject: Reply with quote

Yeah, it's a little confusing, because on the NA, the fans ground through the temp switch, real simple.

The same circuit exists with the Turbo/AC, but they needed to add the extra ground path for when the AC's on... so whereas a relay will normally switch power, this time it's switching the ground path (turning on the extra circuit with AC on)...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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