Coolant temp sensor 1987 300D
 

Had a quick question on 3 pole coolant temp sensor located near the top radiator hose. I power washed the engine and looks like some water got on this sensor, every time I start the car even from cold the aux fan kicks in.
I unplug the sensor the fan goes off.
Question is that my sensor has a RED top and the only ones I see for sale have a blue or green top. Do these units superceed the red top sensor? What are the differences between them?
1987 300D

I deleted the previous post with colors and trip points from memory. Here's info on all but the red switch -

http://www.w124performance.com/image...ch_105-12x.jpg

IIRC the red switch has trip points of 95*C and 105*C. The trip points are etched into the wrench flats of the switch.

Jeremy mentioned that he experienced the aux fan kicking in with the coolant temp gauge around 100*C with a red switch. Then he fitted a new fan clutch and the engine didn't run that hot.

Sixto
87 300D^2

Is this what youare talking about? Auxillary fan switch w133-1630507

http://img.eautopartscatalog.com/liv...1630507BEH.JPG

Charlie

If the first sentence in post #1 is any indication, probably not.

Ok, so the grey switch sounds pretty good. But looks like the red switch has trigger points at 95 wouldnt that make it a better choice? Also I am showing the green switch 0065454524 has superceeded the blue switch.

I missed this line "question on 3 pole coolant temp sensor ". :o

When I read his sensor has a red top, my mind jumped to the sensor I posted.

Charlie

Sixto,

Do you know the thread size of this 006 545 6424 switch? I am doing a feasibility test on eliminating the viscous fan in my 85 300D and need a temp switch to use in the T stat housing to run the electric AC fan as a engine cooling fan.

Good question. I'm without MBs at the moment so I don't have one to measure. FWIW, it's a common temp switch format across OM601/2/3 and M102/3 engines. I'm sure there's a 300E in a scrap yard near you.

Sixto
MB-less

The red switch was never factory installed in a diesel by MB. It shows up in gas-engined cars. Do you need the part #? I have it somewhere.

[edit]

Mercedes-Benz S25/5
Auxiliary fan (high speed) and compressor cut-out switch part numbers are:
• 006 545 64 24 (used in OM603 of '87 300D/TD only) 105ºC/128ºC with blue top
• 006 545 61 24 (used in M102 and OM601 engines plus OM603 of '86/'87 300SDL) 105ºC/120ºC with gray top
• 006 545 45 24 (used in some M103s) 105ºC/115ºC with green top
• 006 545 42 24 (used in M102-3-4 and OM602 engines) 100ºC/110ºC with red top

Don't forget to install a new crush washer if you change switches.

Jeremy

The red switches were used on M102 190E's. I've never understood why Mercedes chose such incredibly high temps for the Diesel cars. The only thing that makes sense is that they were conserving horsepower so the DIN testing looked better.

Funola:

These are 14mm switches. You won't find much selection in that size, especially if you want the double throw functionality. My trick is to remove one of the water gallery plugs on the left side of the head, and replace it with a 22mm fan switch. 22mm switches are used in many VW, Porsche, Jaguar, and Fiat applications. You can find them in setpoints from 72C to 120C. I'm currently using a 95C Porsche switch, and I think the thermal control is as good as it can be. If you wanted to use the electric fans as primary, a set point of 92C, as used in VW's would be perfect. I have access to lots of thermal switch data if you need some help with this.

Also, that isn't the thermostat housing, it's just a coolant outlet.

Thanks for the p/n's . The 006 545 42 24 100ºC/110ºC may be a good choice. Do you know if it's M14 threads?

Please explain what you mean by "Mercedes chose such incredibly high temps for the Diesel cars"? Are you referring to the T-stat temp or the viscous clutch engagement temp?

Did you eliminate the clutch fan and run only the AC electric fan via a 95C temp switch on the head? How does it perform? How often does the fan kick on?

As to whether it's called a thermostat housing or a coolant outlet, how about we call it half a thermostat housing? The thermostat sits halfway in it. The other half sits in the thermostat cover.

Jeremy, I never checked the EPC but memory says Mxfrank is correct about the red top switch being OE on earlier 190E 2.3s.

Mxfrank, the OM602/3 temp switch is 'only' for the aux fan and AC compressor cutoff. Primary cooling is provided by the clutch fan. I don't know the set points of the clutch fan but maybe you know MB spec'd them higher than gasser counterparts.

funola, AFAIK, there is no part of the 601/2/3 thermostat under the turret to which the fan/compressor temp switch and EDS temp sensor attach. All of the thermostat is in the water pump housing at the engine end of the lower radiator hose.

Sixto
MB-less

Yes, but I was referring to the 617.952 housing where I am installing the 602 temp switch.

Ah, yes, that's a thermostat housing :)

Sixto
MB-less

It's incorrect for any car to have 20-30 temperature swings in normal driving. Maybe sitting in traffic on a very hot day or climbing a mountain. But in normal driving, no. These are the only cars I know where such swings are routine, due to a very wacky design. The fans are intended to engage progressively, but even in perfect condition, don't keep temps anywhere near level. And with three separate mechanisms for fan control, the odds of component failure are high. I've heard a lot of excuses for why this should be, not one makes sense.

As a design goal, a cooling system engineer wants to hold temperatures as steady as possible to limit pressure fluctuation. For a cooling system, varying pressure is like flexing a piece of metal until it fatigues. Highly variable pressure will eventually promote component failure.

I use the temp switch to engage the aux fans just prior to the clutch fan engaging. They run quite a bit more than they normally would. But my temperatures stay in a tight range, rarely over 90, and never hit 100. This effectively eliminates the clutch fan, because air temps almost never get hot enough for it to engage. And the added benefit is that I have working A/C, even in heavy traffic.

What year/model Mercedes diesel are you referring to that has a 20 to 30 deg swing? I have currently an 85 and had an 83 300D, and neither one have the swing you mentioned. They stay within 80 to 85 C on the temp gauge both summer and winter with the viscous fan.

I think I will be taking a different approach in controlling the AC aux fan. Rather than adding a temp switch to the T stat housing or the cyl head, I will build a circuit that interface with the coolant temp gauge sender (iirc it is located between glow plugs #2 and 3) to control the AC aux fan. I will make it adjustable so I can have the fan come on earlier or later. It will be less work in the end and provide better temperature control.

Every Mercedes I've ever owned has a "normal" range of at least 30 degrees. Normal driving, they'll hold to 80-85 pretty well. But a hot city traffic or a haul up a mountain road will send the needle soaring. I used to commute to NYC, and it was impossible to use the A/C on a hot day when I was stuck in a jam. A properly controlled electric fan keeps it under control.

Variable fan controls are available cheap, just buy one. But why not try something a little more ambitious...a proportional fan control, which automatically adjusts based on temperature. Some modern cars have this feature built into their ECU's, but I've never seen an aftermarket one that worked reliably.

Viscus fan clutch = "proportional fan control, which automatically adjusts based on temperature". Why re-invent the wheel here?

It is very easy to put a thermostat to control an electric fan and do away with the mechanical fan. Buy a 95C thermo switch ( about $0.50 each or less ) and glue it to the thermostat housing. You can select any temperature you like but use the Normally Open (NO) type. They are used in oven, toaster and are dirt cheap. I use JB weld. The thin layer of glue should be OK as it will not affect the thermoswitch to reach temperature. Connect one end to chassis and the other end to the relay that trigger the Aux fan ( one of the pins in the wiring harness on the 3 pin thermostat ). Bingo - now you have a temperature controlled electric fan. You can also wire it in parallel with the existing circuit, so whichever thermostat reaches temperature will trigger the fan.

Gotta be kidding....

A viscous fan clutch is an on/off device, controlled by ambient air temperature. When it's engaged, it's proportional to engine RPM, which makes it a poor proxy for a coolant thermoswitch. When it's not engaged, it's not proportional to anything. A proprotionally controlled electric fan will turn at a speed that's mapped to coolant temperature.

As for gluing appliance switches to the thermostat housing...doesn't rate a response.

You do not need to take it if you do not like it. This is a free world.

I have not seen anything close to a 30 degrees swing in city traffic in mine, the most I'd say 5 degrees. AC didn't work in the 83. The 85 has AC with R134 but has low charge and bad cooling but neither one suffers the wild swing you experienced.

Found this variable speed fan controller. A bit pricy. Have you seen cheaper?
http://www.summitracing.com/parts/flx-33054

Be nice, he was just giving his opinion, which I agree with BTW.

This one http://www.summitracing.com/parts/flx-31163 has everything needed including a 1/4-18 NPT probe. My T-stat housing has a port with M14 threads. 1/4-18 NPT will go in the M14 but fit loose. I should be able to make it seal with a washer + o-ring +thread sealant.

McMaster has a 1/4-M14 adapter for $7.02

McMaster-Carr

1/4 NPT is very close in dia to M14. It will be on a stand-off and will not be in contact with the coolant.

that's a clever idea.

Where are you putting this that it wouldn't contact the coolant?

Tstat housing

http://i31.photobucket.com/albums/c3...a/image_09.png

I don't see any problem with using an adapter at that point. OTH, a forced-in sensor sealed with goop may give you an unpleasant surprise one day.

I think that you're going to play with the adjustable sensor for a day or so. Once you find the sweet spot, you'll never touch it again. If you have 22mm plugs on the 617 as we have on the 60x engines, it's so much better to use a fixed temperature switch there. You'll probably find a 92 or 95C switch is about perfect: most thermal switches have 8-12 degrees hysteresis, which means your temps will be in the 80-85 range. Even if you have to try two or three switches until you find one you're happy with, it will cost 1/3 the price of the adjustable.

Try something like a Whaler 6010-92, from a VW.