Today, my 1980 300sd was running warm. Almost up to the 120 mark which is unusual, even in town. It cooled off when I ran a long distance with no stops in town.

When I got home, I looked at the radiator for dirt and bugs but it is clean then I saw the electric fan. Started the motor and it did not run but I don't know if it does run all the time. The blade is free and will turn easy manually.

Should this run all the time? Is there a way to test these fans to see if they are OK?

Thanks

From my understanding (limited to say the least ) It should kick it when the engine's getting outside of the "normal" opperating tempature... at least on my motorcycle It does...
I think the way to test for that is to see if it kicks on when its outside of where it normally is... If it doesnt the relay (i think thats how its controlled) is bad... or whatever controls it is bad

~Nate

The "and" doesn't apply to me. My fan only seems to turn on when the AC is on. My radiator does get hot enough without the AC on that is should turn on... Maybe I should turn on the AC to cool it down just kiddin

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B
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1983 300SD

*sigh*

This question has been asked (and answered) so many times it makes me sick heh.


The fan in your 1980 300SD (doesn't matter if it is a w116 or a w126) will NOT come on even if the cooling system is full of superheated plasma...

THERE IS NO COOLANT TEMPERATURE SENSOR TO CONTROL THE AUX. COOLING FAN (on these older models).

It only comes on when the AC system gets past a certain temp.

Most likely you either have low fluid level or your viscious clutched fan is getting weak. Radaitor plugging is unlikely (but possible). Go do a search. Summer was not that long ago.

1984 300d Turbo 134k
Run Engine To Hot Turn Off Engine Move Mech Fan Blade On Engine
By Hand If It Turns Stiff Its Ok , If Free Wheels Replace $160.00
My Other Car Over Heated Replace Fan Clutch Ok, A/c Works Now
$40.00 Diy 1/2 Hr

THERE IS NO COOLANT TEMPERATURE SENSOR TO CONTROL THE AUX. COOLING FAN (on these older models).

Well....my Official Mercedes electrical diagram for my 1980 300SD W-116 chassis shows that EITHER the a/c receiver/dryer temp above 62C OR the coolant temp above 100C will close the aux fan relay and turn on the aux fan. Seems to work that way also.

If I knew how to attach pictures, I would do so...maybe later.

Bob

Mkay...w126 body only then.

It still shouldn't need the aux fan. If it worked its way up to 120C then something is wrong.

I stand corrected. The question just gets asked over and over and over that it gets old...I would think a search would bring up enough.

*shrug*

Where is the aux. fan relay located on a 1985 300SD (126)?

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Bruce

73 220D (never left Germany)
81 300D (totaled)
84 300D (Purchased '03, sold '17)
85 300SD (purchased 10/01/03)

In the fuse box...if you wanna cheat and find it, you can short the terminals of the temp swtich on the AC dryer and you can feel which one clicks.

I have it labeled in my box...if I happen to look at it soon I'll post for ya

Bruce,

1985 300SD has coolant temp control, as well as A/C refrigerant pressure control of the aux. electric fan. The fan has two speeds on the 1985+ 126's.

1981-1984 is refrigerant pressure control only (one speed fan).

Don't know about the 116.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Well....my Official Mercedes electrical diagram for my 1980 300SD W-116 chassis shows that EITHER the a/c receiver/dryer temp above 62C OR the coolant temp above 100C will close the aux fan relay and turn on the aux fan. Seems to work that way also.
My 1980 300SD was the same that is till the deer committed suicide through the aux fan not to mention the rest of the front end. I think I have found a replacement W116 though I will be so happy if I get it!!!
Dave S

Very correct. On my 300SD, the auxillary fan wasn't working for a very long time. However the engine coolant temperature never exceeded 100 C. In fact, I didn't even know my aux. fan wasn't working until it was time for the A/C season and I realized my A/C wasn't cooling as well as it was last year. Eventually I purchased the newer, larger style aux. fan to replace my old one that was destroyed when I hit a deer in June.

I've been a member of this forum for just a little bit longer than you have. Yes it does get annoying to see the same questions asked over and over again, an indication that the individuals asking the questions aren't utilizing the search function, or are having no success when they use it. But just be patient and try to accomodate everyone. Some people have certain problems that they feel they need fresh responses to so they will post new threads instead of searching existing archives. Just human nature you know.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

1985 SD. Thanks for all of the replies. My aux. fan spins fine if I connect it to the battery. However, it has not switched on under any condition. My a/c blows cold. How can I troubleshoot the switches? Where is the temp. switch?
Thanks for any help.

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Bruce

73 220D (never left Germany)
81 300D (totaled)
84 300D (Purchased '03, sold '17)
85 300SD (purchased 10/01/03)

The temperature switch in the A/C system that can turn on the aux. fan is located right on top of the receiver-drier. It is connected to some wires which then lead to the electrical connector for your aux. fan. Should be easy to spot.

Be informed however that just because the aux. fan spins when connected to a battery doesn't mean it is functioning well. You can have an aux. fan spin freely when connected to your battery but then it may blow your fuse every time it attempts to engage while you're driving. If that happens, that would indicate that it is drawing too much current and thus needs to be replaced.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

1985 SD aux. fan. Braverichard, is that the refrigerant temp. switch on top of the a/c rec./dryer? How can I test the refrigerant temperature switch? Where is the coolant temp. switch?

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Bruce

73 220D (never left Germany)
81 300D (totaled)
84 300D (Purchased '03, sold '17)
85 300SD (purchased 10/01/03)