All you W115 owners out there HELP! I am trying to figure out how to test the aux. fan circuit. '76 300D.

I'm wondering if I can take the wire off the switch and ground it out will this make the fan come on? My fan has never come on since I've owned the car. I don't believe it has gotten toooo hot though. It has never gotten above the line just above 175°, I believe this to be the 200°f line. Am I correct here?

If I'm not mistaken , isn't this a 212°f switch?

I have rebled the rear brakes , we will see tonight if it will stop better with a load of Sunday papers. It stopped OK before , but it would nose dive a bit and the front brake would lock up if I really got on 'em.

I still haven't gotten my manual yet so this is all "flying by the seat of my pants" type of work.

The reason I'm trying to get the fan working is because I plan on switching over to straight oil in the next couple of weeks and I will be leaving it running more often. I don't want it to overheat.
Thanks all, Tom

I cant say that I know your car your car for sure, but as far as I know, the auxiliary fan is part of the AC system....it does not go on when coolant heats up......it goes on when the freon in the AC system gets hot...I'd be willing to bet that the AC in your car hasnt worked in a long time, thus explaining why the aux fan hasnt gone on.



Good luck

Mark

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Well, my A/C in fact isn't even there. I have owned the car for only a few months and I have never even seen the Compressor, evreything was removed before I got the car. No, compressor, lines just hanging out linke a big green booger!

Then how is the car supposed to cool itself down when it gets too warm? There must be some way to make it work, even manually.

Wish my manual would get here! Tom

As long as your temperature guage is not approaching the red zone, I wouldn't worry about whether the aux. fan is working or not. I think it is there primarily to compensate for the added load on your engine when you use the air conditioning. If your air conditioning has been removed, then you shouldn't have anything to worry about.

Mike

__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic

That makes me feel a little better! My temp. never gets anywhere near the red zone. There is a line between the 175 mark and the 250? I don't remember what the top number is , anyway there is a line in between the top and the 175° mark and it has been right on that line or slighly ( width of the needle) above it, but NEVER anywhere near the red zone.

That's a few degrees higher than mine usually runs, but well within safe limits. Your thermostat probably just opens a couple of degrees later than mine.

Keep an eye on it in the summer, when the weather gets really hot again. If it stays in that range, then you're fine. I wouldn't spend any money on it unless you're going to resurrect the air conditioning system.

Mike

__________________
_____
1979 300 SD
350,000 miles
_____
1982 300D-gone---sold to a buddy
_____
1985 300TD
270,000 miles
_____
1994 E320
not my favorite, but the wife wanted it

www.myspace.com/mikemover
www.myspace.com/openskystudio
www.myspace.com/speedxband
www.myspace.com/openskyseparators
www.myspace.com/doubledrivemusic

I'm not going to do anything like that! This was a $200 beater that I found hiding out behind a farmers barn. Basically it is a parts car that I am driving every day! I think the reason that it runs a little warmer at times is because I use it to run routes,it only runs up there when I'm delivering papers in town. When I get out in the country it comes right down, and when driving down the hwy. or just regular "normal" driving it sits right on the top of the numbers for 175°F which I feel is probably about "correct" for operating temp.

Thanks for your help! Tom

If they yanked the a/c, then I would jumper the reciever/drier
switch with a switch in the cabin.
Then when you deliver papers in the heat of summer, you have the option of an aux. fan.
We used to do this with all the old 114/115s and it was nice to have. Those old fans really sing........

Mine runs at 180 normally, sometimes a bit higher if sittng in traffic. This is with no AC on.

Just a note. If your coolant level gets too low (just replaced my water pump) you will have no heat.

Thanks to all, Arthur I will look into the fan hookup in the a.m. it shouldn't be a real big deal as it sounds pretty straight forward. ( I wonder if this is what is wrong with my buddies '79 300SD, he bought a new fan and it still don't work! $200 for a fan *ouch*)

As far as the "heat hint", I do have heat, but not when I turn on the heater blower. I think there is a door that ins't opening like it should. I have't really been concerned about it though as it hasn't gotten really cold yet and the "flow through" that I get just driving down the road has been sufficient. The P.O. also had his little fingers in there too. Evidently the fan switch wasn't working so he did something and wired it into an on/off switch for the blower, consequently it only works on high. That is ok with me though, the reason I turn on the fan (heater) is so I can get warm, fast . Personally I never understood why we needed BOTH temp. control AND variable speed fans, in my opinion one or the other is sufficient!

Tom
(chairman of the easy-to-please dept.)

I was looking at the electrical schematic today and noticed the aux fan is controlled by two things, 1) the water temp switch located on your thermostat housing and 2) an ACswitch, location unknown ATT.
the water temp switch is valued at 100deg C or 212 deg F. If you stick it in a pot of boiling water with meter hooked up you could verify it's operation. Also you can hit the fan with 12v from a battery charger to test it, that's how I tested mine. AC switch ?

Greetings Fryer,

As Dalton mentioned you can bypass the switch on your reciever drier to start the cooling fan, and on some models there was also a coolant temp sensor in the thermostat top with a wire going to it. Grounding this wire also made the fan start up as well. This one depends on whether the PO left the original engine in or if you have a replacement. In most cases if your car had a/c it most likely had a clutch driven cooling fan which will keep up with your engine cooling needs as long as your don't have a/c to contend with overheating your engine.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

I must add to your above statement...grounding that wire will work ONLY if the switch on the A/C drier is in operating condition. This is what had me going, I tried to ground it out first thing and it didn't work. When I pulled the wires off the drier, the clips were severely rusted, I cleaned them up and used a jumper wire and the fan came on!

I ran the aux. fan while on the first route today. ( temps outside near 60°F) It made NO difference at all in the engine temp. It's still just above the 200? line. Now I'm starting to think maybe thermostat or the clutch fan isn't working well enough. Here is why I'm going this route. When I turn the levers on for the heat but don't use the blower fan the temp. will drop almost immediately about 5-10 degrees and stay pretty steady. That leads me to believe that I'm not getting sufficient circulation. I'm thinking that would either be water pump or else the thermostat isn't opening all the way. ( since I can't afford a water pump right now, I deduce that it must be the thermostat )

I'm about to head back out on the second route now and I'll check the coolant level and start the car and see what I can learn about the circulation in the radiator. I remember having watched the temp. real close on a Rabbit one time and I learned that it actually ran warmer in the winter with the heater on than it did with the heater off. ( position of the thermostat exposed it to the elements and it wouldn't open as well, it was in front of hte engine on the bottom near the oil pan) In may case that meant the perfect spot to be in contact with all the snow and ice that I was "pushing" through and it was packed full all around it! Cleared it off and 'voila, everything was right again!

Greetings,

This is just a thought, but maybe your self made fuel actually burns hotter than diesel fuel does. If it burns hotter than it's possible that the thermostat that you have installed is wide open but regardless, can't keep the temp where you think it should be. Do you notice a decrease in engine temp when just cruising down the road at let's say 40-45 verses 55-60? The thermostat only opens so much regardless of what the engine temp continues to climb to. It's possible the BTU factor of your fuel is just that much hotter than diesel fuel, hence running a little warmer all the time. I guess one way to tell is to remove the thermostat all together and see where the temp gauge ends up and how long it takes to get there.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

It was a thermostat, it was quite old . Threre was rubber inthe center part of the stat that had broken down and was crumbling and it looks like it was "binding" and causing the problem. All is cool now, well steady with the needle going straight through the 175 numbers, so that is about 180°. I was running on straight pump fuel BTW I've been too busy to make any fuel this week. Tom