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#1
12-07-2012, 06:39 AM
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1971 300SEL 3.5: aux fan not working
My aux fan is not kicking in, no matter what coolant temperatures, also not when AC is on.
If I ground the coolant temperature switch the fan comes on. I guess the fan should kick in 1) if coolant temperatures are at around 97C plus 2) if temperature at drier switch is 62 C plus So the fan itself works...I guess the relay also works.... The temperature switch is dead? Can I exchange without draining the coolant? Why does the AC not turn the fan on? Jumping the 62C switch should turn the aux fan on permanently? I'll try to jump the drier switch and report back. Best, Martin 
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#2
12-07-2012, 09:59 AM
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I just come back from the car.
I jumpered the temp switch wires at the drier.... now the aux fan is running permanently...is there anything wrong with running the aux fan all the time? Well, at least until I have found the reason for the not working switches I'll keep the aux fan running. I notice a much better cooling...okay it was night here and ambient a couple degrees lower but still. vent temps were right away at 3- 6 Celsius- so the fan is doing something. I'll attach a picture of the 97C temp switch and a picture how it should look... doesn't match with a picture how it should look. the connector looks very different. Any idea? I also have another switch here..but this one looks very different ( third picture) again at the bottom part that goes into the coolant housing. Last edited by werminghausen; 12-07-2012 at 12:09 PM.
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#3
12-07-2012, 10:07 AM
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Martin,
Best thing to do is to run a ground wire from the Aux fan relay or sensor to a new switch that you put under your dashboard. That way you can switch the aux fan on whenever you want. MB liked to switch the ground circuit so it is very easy to pull a from the sensor or relay into the cabin and have a ground somewhere under the dash. I had/have the same problem (sensor does not work) and have a switch for it now so I could override the sensor. I frankly never had to use it because my cooling systems works wonderfull - even in summer in Atlanta. Must be the new radiator that a PO installed 15 years ago.  Good luck, Bert
__________________
'70 111 280SE/c 3.5 (4 spd manual) - sold '63 MGB '73 MGBGT V8
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#4
12-07-2012, 12:12 PM
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Can't be so difficult to change this 100C switch? Do I need to drain the cooling fluid?
How about changing the thermostat at the same time?
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#5
12-07-2012, 12:18 PM
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You can certainly change the thermostat at the same time but this point is higher than the radiator so you're not going to lose all your coolant when you remove the sensor. If I were you, and if the coolant is good, I'd just remove the sensor and quickly put the new one in. Some will be lost, but not a lot.
Best Regards, David
__________________
_____________________________________________ 2000 Honda Accord V6 137k miles 1972 300SEL 4.5 98k miles _____________________________________________
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#6
12-07-2012, 06:15 PM
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GET AN INLINE FUSE ON THAT AUX FAN !!!
A number of D models have burned to the ground over that circuit causing a fire. Several threads here with pics to prove its well worth it.
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#7
12-08-2012, 01:37 PM
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You are saying add another fuse directly into the line of the fan.... I thought it has a fuse at the firewall?
What size fuse are you talking about? Martin Quote:
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#8
12-08-2012, 01:41 PM
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Thanks, I think
I'll release some coolant and change the thermostat at the same time. Quote:
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#9
12-09-2012, 01:45 AM
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The typical fuse added to the 300D series is a one amp.
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#10
12-09-2012, 12:58 PM
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With D - model you meant a diesel... not a D-jet?
1 Amp is a bit low??? Quote:
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#11
12-09-2012, 06:36 PM
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No, 1 amp is the correct fuse for the aux pump.
__________________
1985 300D 198K sold 1982 300D 202K 1989 300E 125K 1992 940T "If you dont have time to do it safely, you dont have time to do it" "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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#12
12-10-2012, 02:22 AM
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Answer
Quote:
Auxiliary Fan Switch MB# 003-545-24-24 Pelican Parts - Automotive Parts and Accessories - Porsche & BMW .
__________________
ASE Master Mechanic asemastermechanic@juno.com Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 1984 190D 2003 Volvo V70 2002 Honda Civic https://www.boldegoist.com/
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#13
12-12-2012, 12:13 PM
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Quote:
quite expensive this beast? I'll look for something here in Oman and Araboan desert...but not easy. Do you think the switch I have (third picture) might work? Other wise I 'd just jump the temperature switch for the AC and keep the auxfan running permanently. I also found that my engine is overheating a lot if I get stuck in traffic. I easily reach 220 and over close to the red mark. What do you think this is? Also starting the engine becomes problematic if the engine is overly hot.. What is this? martin
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#14
12-12-2012, 06:42 PM
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Your third pic sensor is stock on the 4.5 but works identical to the 3.5. As long as you can fit it in your manifold, then it'll work - you'll obviously need to solder a new connecter on since it's a different style.
__________________
Current: 2021 Charger Scat Pack Widebody "Sinabee" 2018 Durango R/T Previous: 1972 280SE 4.5 2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi" 1999 Chrysler 300M - RIP @ 221k
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#15
12-13-2012, 03:36 AM
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Quote:
Fit in the manifold: you mean the length of the piece sticking into the manifold? And thread size...but I think thread should be the same...I hope. Any chance to test the switch if it works or not.... I guess boil water (100C), put switch in and measure continuity between pin and body of the switch? Martin Last edited by werminghausen; 12-13-2012 at 08:31 AM.
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