Well, if I didn't speak too soon! ['87 300D aux fan] - PeachParts Mercedes-Benz Forum

Adenauer · #1 10-05-2007, 09:02 PM

What is an amazing thought is that as I write this, somewhere in most every corner of the globe right now (and surely, right here in the US) is a Mercedes with its owner giving it some attention on some level. Aside from hanging out here on a Friday evening, browsing the threads at MercedesShop, what are you guys working on?

At any rate. The other day, I posted a comment about having pressure washed the engine area of my '87 300D. I followed-up with a post indicating that the auxiliary fan was running with the key in all postions, stone cold engine, and A/C off. Another member pointed out that possibly a wire was knocked loose. After checking, I did, find a wire had been knocked loose from the compressor switch on the receiver/dryer. I had been spraying from below the car in a service pit. After placing the wire back where it belonged, all has been well until this morning. Same symptoms...key in all poistions (except, of course, off), cold engine (as well as normal operating temperature), and A/C compressor engaged - or, not.

I have visually inspected every single component under the hood today. I have also flip-flopped relays C and D in the component box (I installed E-code Bosch headlights over the summer so relay D is no longer used for the headlight washer system); same deal - fan still runs on its own. The Klima relay is about a year old by looking at service records. A/C compressor seems to cycle as normal on all settings. I did not swap a relay into position B. If I understand correctly, isn't position B the aux fan pre-resistor relay?

Every other system on this car is in fully operable condition. I have spent a couple of hours browsing past threads relating to the aux fan and have not really found anything relevant. The car hasn't been driven as much in the last few weeks as I've been driving my in-law's W210 while they are away for a couple of months. I just would rather not burn-up the fan motor without troubleshooting this. Questions, comments; concerns?

Also, now that the engine is nice and clean, I have noticed a very slight seeping of oil from around the base of a cylinder head bolt. The bolt is just forward of the charged air crossover pipe on the driver's side. Am I right that the head bolts are a one time only 'ride at the fair' and that perhaps this bolt has stretched? Is it possible to simply install a new head bolt in its place and torque to specs? So far, no oil in coolant; no coolant in oil (by visual means).

I'd be happy to spring for coffee and donuts for everyone in the morning but thank you, in any case, for the help!

Tom

I would, too. Just so you know.

cencarnacion · #2 12-09-2007, 11:00 PM

Adenauer,

Did you get your problem resolved. I am experiencing similar issues with a similar background. I cleaned the engine of my 87 SDL using Engine Brite and water spray. Now the auxiliary fan runs all the time and to add salt to the injury, the A/C no longer blows cold air. I am new to MBs but I am thinking that the fan runs because a "sensor" thinks the engine is running hot and the A/C compressor won't engage because the engine is supposedly running hot.

Any ideas?

cencarnacion · #3 12-10-2007, 08:53 PM

I talked to a cousin who owns an MB repair shop in Lancaster, CA. When I washed the engine, he says that I ruined a temp switch that controls the auxiliary fan. This is a common problem. The temp switch has to be sealed with silicon RTV to protect it from water.

I trust the diagnosis not only because he is my cousin but also because as soon as I spoke of washing the engine, he immediately told me that my auxiliary fan continuously runs and that the AC is not blowing cold. I asked how he knew that. He says it is a common problem.

He will be ordering the part for me. I will post what it is exactly called including part number.

Another caveat when cleaning the engine is to keep water away from the air filter and duct to the engine. Water in the engine is quick way to ruin a good engine.

Hope this helps.

pawoSD · #4 12-10-2007, 08:56 PM

Perhaps these engines just don't like getting a bath?

I leave mine nice and dirty, then I know it can't get any dirtier!

As for the fan running, I believe the temperature switch on the A/C Recieiver dryer can fail in an open or closed postion....yours may have failed in the closed position, causing the fan to run no matter what....

babymog · #5 12-10-2007, 09:27 PM

I had a similar problem with an '87 after washing the engine with Simple Green Max and a hose. I un-plugged the fan and used it, parked it in the garage overnight, plugged the fan back in and all was well for the next year I owned it.

Bio300TDTdriver · #6 12-11-2007, 01:45 AM

You most likely got this switch wet, http://img.eautopartscatalog.com/live/C602025584BEH.JPG ,which is causing a short. Unplug the double wire for a couple days as babymog did. Yours might be a different color depending on which one you have. If you do a search for Auxiliary Temperature switch there is quite a bit of information on here about it.

http://www.peachparts.com/shopforum/showthread.php?t=158031&highlight=auxiliary+temp
See post #2.
Chris