WRD - Warm Running Device Shutoff Temperature

[TJMart]

I did the Linkage tour and got my ignition system set up with correct plugs, wires, points etc. and timing. It idles and runs very good now when it is at temperature after several mixture adjustments using the adjustment wheel on the back of the pump and fine tuned it with the large air screw.

I now want to tackle my cold start idle problem on my 1970 280 SL during warm up. It is running too rich (splitting the linkage) and it is not even close to the 1000 - 1100 RPM when cold. I read in the Technical manual that you must first set the WRD shutoff at between 149 and 158 degrees but also saw in the BBB that starting with USA versions in 1970 models the shut off should be at between 122 and 131 degrees. This must be done with adding or subtracting round "washer shims" below the thermostat before you proceed to adjust the overall warm up  mixture with the oval shims underneath the WRD.

My WRD shuts off at just below 180 degrees according to my temperature gauge on the dash which is almost at operating temperature. This does not seem to be a very accurate way to determine what the actual temp is. Based on my research I will need to add "washer shims" to get it to shut off sooner.

I can't seem to figure out how to test the coolant temperature at various stages of warm up especially when the WRD shuts off. Need some advice on this. I can also measure it when I add washers to see that it shuts off at the correct temperature.

If I set it to shutoff at between 122 and 131 degrees instead of the 149 to 158 degrees, how will that affect the mixture from the time the WRD shuts off to the time it reaches operating temperature of 79 degrees Celsius or 174 degrees Fahrenheit?

Thanks in advance!

Tony

[rwmastel]

I believe I recall members putting their WRD and a thermometer in a pot of water on the stove, and watching the device behavior as temperature increases.

Someone please let me know it my memory is good or bad!!

[BartSt]

Here is a big part of your solution I think

https://www.youtube.com/watch?v=F6sxlOFmoYw

Best

Bart

[bracurrie]

Look, I am not an expert vintage Mercedes tech. But while I find the information on the YouTube referenced on this thread December 2nd seems to work, I don't believe his technique for setting idle mixture warm is technically correct.  The video description of setting the WRD seems valid.  My question would be is there an advantage to setting the cutoff temperature higher? Was it set low for the emissions constraints of 1970?
Brad

[TJMart]

Look, I am not an expert vintage Mercedes tech. But while I find the information on the YouTube referenced on this thread December 2nd seems to work, I don't believe his technique for setting idle mixture warm is technically correct.  The video description of setting the WRD seems valid.  My question would be is there an advantage to setting the cutoff temperature higher? Was it set low for the emissions constraints of 1970?
Brad

Yeah that was my point in the last paragraph of my post. I recall reading a post about the so called "lean dip" that occurs after the WRD shuts off until the engine reaches operating temperature. I agree that it seems that emissions was the main reason for setting it to shut off approx 25 degrees sooner. It appears to me that emissions are not a factor anymore for this old of a car and if I set it at the emissions temp then the lean dip time would be longer. How much would this affect the way it runs and running leaner would it cause any harm or damage to the engine?

[rwmastel]

Tony,

You said "I can't seem to figure out how to test the coolant temperature at various stages of warm up especially when the WRD shuts off. Need some advice on this." That's why I suggested the hot water on the stove.  You can learn the exact temp at which the device starts moving, and the temp where the device is fully extended.  Then you just have to do the adjustments with internal washers (air) and large shims (fuel).

Does the device ever "wear out" and not fully extend anymore?
Is there a known measurement for full extension?

[TJMart]

Thanks to all for your replies! I wanted to give an update on my progress. I took out the WRD and took some measurements of the WRD pin, not the thermostat pin! at cold temperature (fully pushed in) and it was 8mm. Pulled the pin out and it measured 16mm fully extended. I took Rodd's advice and used a pan of water and suspended my WRD upside down in the water with the thermostat at the bottom so that the temperature measured was the water temperature and not the bottom of the pan.

I turned on the stove and just watched the "valve" of the WRD to see at what temperature the valve completely closed. Since my car is a 1970 the BBB calls for shutoff at between 122 and 131 degrees. My valve was almost completely closed at 122 but did not fully close until 142 degrees. I took the temperature again at 174 degrees (engine thermostat temperature) and measured the pin fully extended and it was 14mm.

I took the WRD device completely apart and cleaned it and slightly lubricated the valve and the inner shaft of the WRD to prevent any sticking. I reassembled the WRD and did another test. This time the valve fully closed at 122 degrees and the pin, fully extended at 174 degrees, measured 16mm.

I assume my WRD is working properly now since the valve completely shut it off at 122 degrees and the pin was extended to the max at operating temperature.

I will now reinstall it and see if the WRD is too rich or too lean and will adjust the mixture by adding or removing oval shims. It seems that this will be trial and error. I hope to reach a peak of 1000 to 1100 RPMs during warmup gradually declining to 800 RPMs when operating temp is reached.

Any thoughts or advice is appreciated!

Tony

[rwmastel]

Tony,

So glad you're making logical, factual, systematic progress!

The YouTube link posted above by BartSt helps explain the function and trial & error adjustment of the WRD.  Internal washers adjust the supplemental air, and the external shims adjust the supplemental fuel.  It helped me, but could have presented the same info in half the time (or less).