gotcha so if it shows that airflow could be a problem, then what do I look at next? There's nothing blocking the airflow to the radiator (as far as I can see). Also, it's not very hot yet nor am I in bumper to bumper stop and go, which I'm guessin would also cause airflow issues..

AF blockage on a/c cars is usually between the condenser and the radiator... it could also be a bad viscous fan coupling.
Many guys also bridge the blu fan sensor with a resistor to make the high fan come on at a lower cut-in spec [ I like around 100C]..that only cost a buck or two and is a common mod for 104 ...

Be aware that Benz does not consider 110 to be overheat under certain ambients/condition...[ butI do]...just make sure the high fan triggers a 105/107 C. That circuit can be tested by simply pulling the connector off the blu sensor and see if the high fan defaults...that is another simple test for high fan circuit integrity.......

I did replace the fan clutch recently (I think that's aka viscous fan coupling), so that shouldn't be an issue...

I like the idea of the resistor to trigger the fans at a lower temp, so I will look into that....

But for the basic issue of a possible block.. I'm still not sure how to go about looking for this. Is it a matter of replacing pipes? Parts? I did notice something a while back where the hose (pointing to it with the red arrow) was sucked in by something creating a vacuum - engine was hot but just turned off.

Check overflow tank cap ...that is the most common, but could also be a weak hose or air block/lock in system, requiring bleeding.

Have you done any recent cooling sys work?

Only thing I can think of is replacing a stuck thermostat and topping up some of the coolant that spilled during that replacement.

Yes - I should probably replace the overflow tank cap (that probably could have caused that vacuum)...

But back to the blockage... lol... am I looking inside hoses or parts for a blockage? And is it some physical debris that I'm looking for or a stuck part? Kind of lost..

<am I looking inside hoses or parts for a blockage? >


...No...air flow blockage...like dirt/debies/leaves/etc..they get in the fins and degrade the cooling effectivity........................
A good hose and soap cleaning of the cond and radiator fins ....I am not tralking about a water blockage...I am talking Air flow bockage....that is why I had you do the low fan jumper test.

ah gotcha... cleaning the rad should be relatively straight-forward

another question... when you say condenser are you referring to the AC condenser or something else? I tried googling pics and all I got were AC condensers. If it's the AC condenser, how do I get to trying to unblock an AF issue here?

Listen

The ac cond has fins...the ac cond is in FRONT of the radiator...if the fins of the cond are full of dirt and debries , then the air can not get to the radiator..see?
So , the rad has a problem cooling b/c it has rstricted air flow.
That is the gest of it.
The ac cond gets cleaned with a garden hose and soap spray..just like you would clean your house ac unit. Then , you can seperate the rad and cond on top a bit and look in between the two for debries and leaves and such...they inhibit flow ..it is that simple.

Sorry to interrupt this, but early in this thread, there was mention of adding a resistor to get the fans to turn on a few degrees earlier and I had two questions. Are there any drawbacks to doing this mod? Why would one make them go on a few degrees cooler (e.g. 92 vs 103) instead of a lot cooler (e.g. 80 vs 103) ??

Thanks!

Why would you want the fans to come on @ 80C with a thermostat that is spec. to start to open @ 87C ???

The thermo is trying to get the engine coolant temp up to optimum operating design range and you are adding fans to hinder that operation.

My wife does that..she heats the coffee in the microwave until it is too hot to drink and then adds an ice cube.... :)
These are AUX fans, not cooling system fans..and are not designed to run all the time b/c they have an adverse demand on the electrical sytem and the fans themselves.
Also , that Blu sensor [ Termistor] is actually the ACC Module control temp input and a radical change in the cut-in of this sensor will also adversely effect the A/C Compressor CUT-OUT spec.... in other words , do not assume that the sensor is used just for the aux fan trigger..that is just one of it's functions. And changing it's value effects ALL other funtions.
That is of important concern.

It's just a question - I don't know very much about the operation of these things, and I'm seeking to understand :) Now I know those fans are auxilliary, and not system cooling. I'm looking at doing the mod on my 1995 s320 (w140 body) based on this, however, I cannot find anywhere that has 1.1k resistors, only 1k or 1.2k.

Based on what you wrote below, it sounds like it would be "safer" to have the fans turn on a little warmer (e.g. use the 1.2k) than a little earlier (e.g. 1k). I'm using the comparison from that website, where he states the 92 degree @ 1.1k is preferred, versus the 95 degree @ 1.2k. Again, I cannot find 1.1k resistors anywhere.

hanks!

You have a 104 engine and they do not have the common heat concerns of the V8, so, I have found the hiigher R value is much better for the 104 cooling system.
I find a cut-in of 100C to be perfectly adequate for the HFM/SFI /104 system after much experimentation and thoughts. The exception to that would be in Extremely HOT climates.........
In that case . I am an advocate of a manual Low Fan over-ride to get a jump on any adverse High Temp Thermal Load condition. And a lower temp thermo............
Don't be fooled that lower is better. And it is a preference call, so do as you like

The logic behind my findings of 100C CUT-IN is the fact that if one has a fan cut in @ 100C, then it will lower the offending temp increase well before factory 105/107 spec. , but not prematurely. Once the temp start to come back down from the aide of the added aux airflow, the CUT-OUT of this mod will be approx. 95C. Which happens to be the IDEAL operating temp for 104/HFM engines. This is called the TEMP spec Differential [ the difference between the cut-in and the cut-out]...so , if you get the engine back to optimal operating temp of 95C, you want the fans to turn OFF, as they have curbed the creaping heat increase are NO longer needed . This gets you over-heat protection faster than Factory spec of 105c, while still using the fans draw demands as little as possible , and at the same time , having very little effect on ACC Comp cut-out. Just my design
opinion.
I also will add that when doing any of these mods where you are using the temp gauge as your reference readout, I alway check the accuracy of the gauge FIRST to assure it is accurate..otherwise you will be working against yourself.
An easy verification on that one is to sub a high tolerence resistor of 38 ohms in place of that sensor , at which time your gauge shoud read exactly 100C............................

How do get past the A/C condensor?
 

I don't understand--even if you tilt back the radiator, there is still the issue of the A/C condensor, which is located between the radiator and the fans. Are there any photos for this DIY?

you guys seem to have forgotten that the radiator has aluminium tubes in it.after 5-7yrs the tubes will have shrunk.typical symptoms are rising of the engine temp at idle[even with known good fan clutch]which then falls as soon as the engine rpms pick up[running water pump at higher speed and forcing higher volume of coolant through restricted tubes]i went through a lot of agro back in 1984 figuring out this one.