Does the OM617 have an Aux Fan Switch?
 

I am trying to get rid of an unreliable thermostatic fan switch (probe into radiator fins) that runs my electric cooling fan on my OM617.951 out of an 85 300sd. There is what looks to be some sort temp switch on the thermostat housing that is unused (by me atleat). Is that a temp switch, and if so, anyone know what temp it triggers at? If its around 190-200f then I can hook it up to my fan relay. Thanks.

The aux fan is there to reduce excessive high side pressure. There is a temp actuated switch in the reciever drier at the front, passenger side of the engine compartment.

are there any markings on the switch you are eyeing? likely it's a temp probe, not a switch. designed to sense coolant temp for the climate control delay.

The engine is in my Jeep. So that wouldnt really apply. As to the probe/switch on the t-stat housing, I will take a look when I get home.

My 617.950 has an 'inverted bell' looking single-pole switch in the thermostat housing that turns on the cooling fan at 100°C. The electric fan is simultaneously controlled by A/C high pressure side. This switch appeared on many Benz's from the 1960's through the 1970's.

http://www.***********************/images/apw_products/images/WORLDPAC/W01331630507BEH.JPG

IIRC, the part number is W0133-1630507...

Realized I had a pic on my phone. Turns out there are two switches/sending units as shown in the pic. So is one of these the heater control and the other the aux fan control??

Attachment 111843

One is for the climate control, one is for the EGR computer.

-J

There are these two pieces in the thermostat housing

http://i.imgur.com/U1Dwm.jpg

I'm doing a swap with an om617 and don't think I need either as I'm using the native cars cooling system. The probe on the left is the aux cooling switch?

What is the probe on the right with dual vacuum lines going into it?

In my 1984 & 85 300D w/ OM617 turbo engine, the aux fan is turned on solely by a temperature switch that screws into the top of the AC filter/drier (no pressure penetration). That switch actuates a relay that sits under a plastic cover on the driver's inner fender.

The two thermal sensors you ponder in the T-stat housing are:

Electrical temp switch that prevents the cabin blower from turning on until the engine coolant gets "hot enough", i.e. so fussy rich people won't have cold air blow in their face. Germans are taught young to fear any drafts.

Vacuum temp switch that is part of the very complicated EGR controls "analog computer".

But, no reason you can't operate the radiator fan by a coolant temperature switch. If smart, you can wire in parallel so that any of the 3 things could command "fan on" - AC liquid temp, coolant temp, tranny oil temp. Sounds like M-B did such earlier, but no need to leverage that since there are many fan controllers in tuner world, just browse Summit and Jegs catalogs, or ebay/amazon.

Thanks Billgrissom,

The swap I'm doing is into a early 90's toyota, and the coolant system in the truck has all the necessary sensors in its system that will fit onto the merc engine.

I'm also planning to remove the EGR w/ block offs, so it doesn't sound like I'll need to worry about reconnecting the two piece vaccum lines, right?