A very strange thing happened to my 86 300sdl yesterday. It has a 6 month old battery and it died yesterday while it was parked in my lot at work. Strange thing too, because it was a beautiful 75 degree sunny day.
I had to manually unlock the doors and the trunk, retrieved my jumper cables and hooked them up to my friend's Ford F150. As I hooked up the jumpers, I noticed my aux fan was turning. Everything in the car was off. When I tried to start the car, it would barely turn over, but the aux fan was turning at high speed. I opened the fusebox and removed fuse number 1 and the aux fan shut off and the car started immediately.
I drove home and started to investigate what could be wrong. I dug out the electrical schematic and started to read. I put the fuse back in fuse number 1 and the fan immediately started to run at high speed. I located the aux fan relay in the fusebox and pulled it and the fan stopped. I plugged it back in and the fan started. I unplugged it again and replaced it with one of the other relays ( the one from the power windows) and the fan stayed off.
I believe that my relayy stuck in the on position ( probably old age) and my aux fan killed the battery.
Luckily I have a large stash of used parts and found another relay and plugged it in the power window relay location, charged up the battery overnight, and all seems well. I will monitor to see if the fan comes on again while the car is off.

__________________
John
1986 300sdl
1985 380se

Thanks, John. I have an 87 and will try to remember this.

It could also be the water temperature sensor....

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

You know it could be. Do you happen to know what the temp sensor should ohm out to be?

__________________
John
1986 300sdl
1985 380se

no, sorry. what I did on mine was to pull the relay and put a new one back in from another part of the box. Can't remember where from now, but the fan still ran. Asked here, and they said to unplug the water temp sensor and see if that helps. So, I did that, and it stopped. put a new sensor in, and no more problem with that...

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

Then replacing the relay wouldn't have fixed the problem.

It is easy enough to test the relay with an ohmmeter.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

You came very close to the verification it was the relay. Had you removed the one that allowed the fan to stop and inserted the bad one again. If the fan ran it would have verified the relay was bad. You were very close and at the present it does look like a relay fault. If you were to put the old one back in now for just an instant and the fan started it is a positive verification
99 1/2 percent of the time.

This verification process is actually more important if the fan would not come on at all. It basically helps or eliminates the chance of something like terminal corrosion being behind the issue. Also you have no way of knowing used parts or even new are good other than with some form of verification sometimes.

This type of habit is developed over time. I dislike any kind os shotgun approach as well. You may never be able to prove or know what the original actual defect was. You only knew the problem. Although with certain intermittent conditions you might be reduced to doing it.

I have an '86 SDL and my battery keeps dying if I don't use the car at least once every 3 days. But 4 days ago the starter was hardly able to turn over the engine and while it was struggling to do so I noticed that the windshield wiper started moving, slowly but surely it went up and down till finally the car started and then the wiper stopped. I drove to work, about 20 miles and in the evening when I tied to start the car it did exactly the same thing. that evening I used a charger and after 2 days when I tried to start the car the battery didn't seem to have enough power. It did start after a bit of a struggle though.
How is the wiper electrics tied into the starter circuit? What do you think would cause this to happen?
Thanks for your help and advice, I have found this forum a life saver in the past.

__________________
AJ
82 300D
81 240D
76 450SE
86 300SDL

Well, before you investigate the wiper further it sounds like you need to check both your battery and alternator.

it couldn't be the temp sensor I don't think... with the key off, the temp cannot engage the aux fan... please correct me if I'm wrong.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The water temp switch on my car went bad, and the aux fan stayed on all night... Replaced the sensor/switch, and the problem stopped...

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

Something wrong with your car wiring. The aux fan should NOT come on with key not in run position.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Very possible... I had to rebuild the cabin wiring harness about a year after buying the car... the whole thing melted... It's not impossible to think that something else went wrong...

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

Thanks Kevin, looks like I have a bad battery after all. Reads only 11 volts, but still starts the car, and the wiper still moves when cranking. Strange.
How do I check the alternator? I have heard that this could be a problem with battery drain. My car used to still go dead when the battery was new if I did not use for a week or so.

__________________
AJ
82 300D
81 240D
76 450SE
86 300SDL

Thanks vstech, my aux fan did not come on, it was my wiper.

__________________
AJ
82 300D
81 240D
76 450SE
86 300SDL