Did I destroy the thermometer capilary?

[Miloslav Maun]

What an idiot am I?
I spent 2 nice hours in the garage removing all the instruments. Everything went smoothly. The last one was the center combined unit with fuel gauge, oil pressure and thermoeter. I was surprised the thermometer is not connected with a cable, it was kind of strange thin tube... I tried to disconnect the tube from the gauge but no succes. Eventually I left the gauge in the car unscrewing it from the rest of the unit.
Later in the evening I read in my clever book that it is very important not to bend the lead to the thermometer gauge. I was turning it around, twisting it and so on. I did not use much of brute force but anyway, how fragile it this thing? Did I break it? Do I have to go and buy a new one for $200  :evil:
I have no engine in the car right now. This gauge is reading about 220 F. What is the principle of this device? How does it work?

Thanks for opinions...

[waltklatt]

Muf,
Was/Is there a funny sweet smell? when you moved the capilliary tube?
It's durable to a point and then it breaks.  
If in doubt then you can take a lighter and hold the flame under the large insert that is in the engine bay(part that plugs into the head), and watch the needle move up.  If it moves after a while, then you can count your blessings.  But if it wont move, then you will need to make your wallet lighter.
Walter Klatt
1967 220SL-diesel-converted to electric
1963 230SL-gas-original

[rwmastel]

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Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Cees Klumper]

I broke mine without realising it and, (only) when I took the car out the next time, I noticed that strong smell that reminded me of all of those previous posts telling me to watch out for ... that strong smell. So I had to shell out the >$200 ...
I am probably in one of those threads that Rodd dug up for us.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Miloslav Maun]

Yes, Cees, I have read about your sad story :-(
I do not believe I broke it. First, I did not smell anything and second, I was not too brutal. I am only afraid that I might bend it and thus squeezing the inner diameter of the capillary.
BTW: How does the device work? Is the gas inside kind of transmitter?

Anyway, this is a really stupid technology. I thought mercedes was known for invention and this looks like a poor solution. Why did not they simply install a sensor on the engine and then lead wires up to the dash :-(!

[Jonny B]

All that is at work here is the theory of expansion. When the bulb gets warmer the fluid inside expands and then, via a mechanical link, moves the pointer for the gauge. If not nicked, this is quite a reliable and repeatable set up. So this time, perhaps innovation was not as important as reliability (something MB should be looking at again, given the poor quality record of recent years).

Jonny B
1967 250SL Auto

[Miloslav Maun]

I am here again!
We have managed to get the unit out. I have heated the bulb on the other end and the hand moves like hell! So it looks like it is not all broken after all. But just misalgined or what? The standard position is at some 250 °F and when you heat the other end the hand goes off the scale.
Now what? Any ideas how to adjust the zero position?
Thanks

[Cees Klumper]

Maybe just try to move the internal mechanism vs the dial positioning, if you know what I mean. From my memory, I believe this can be done (gently!)

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Benz Dr.]

You have to remove the whole unit as one piece. This means the gauge along with the capilary tube and the end that sits in the housing on the side of the head or directly into the head, depending on what engine you have. Removal at the head is where most people run into trouble. You can snap the tube off by turning the gland nut if the bulb on the end of the caplilary tube decides to tun with the nut. The trick is to undo the nut a little bit so that the bulb can be turned a little. What you don't want is to have the tube and the nut turning at the same time - it will definatly break off. Hold the end of the tube lightly with vice grips while turning the nut but not so tightly that it will crush the tube. Use something like liquid wrench and the nut should start to turn.
I use anti sieze all around the bulb and work it in well as I install this piece. You never know when you might need to take it apart again. ( In my case, too often )
You can always pull the housing on the side of the head which uses the only 15 mm sized screw on the whole car to hold it on. I do this as a standard procedure on some jobs as I can turn the housing around without twisting the tube if I really have to take it apart. If you're just going to remove the head leave this alone and pull the housing. Late 280 for US market may not have this option.

Never take anything apart because you want to see how it works ( I do but that's diferent - I need to know ) or take anything off that you don't need to remove. Call me for parts otherwise...... anyone who can't follow this better call me.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Miloslav Maun]

UPDATE:
I have unscrewed the back plate, the black dial and the two screws inside the gauge so that I was able to remove the inside mechanism (the gear and toothed pendulum). Thus I gave the hand a different dead position (after about a dozen of try-and-error alignment efforts). When the zero position seemed to be OK, I took the whole thing to the kitchen and inserted the sensor into a cup of boiling water. The hand rose almost to the 100 °C mark. Not 100% accurate, just about 1 mm below, but anyway, I am happy with the result.
I hope the damn thing will work when reinstalled (I will know in about 2 months).
But I still do not understand the initial reason why the hand changed its zero position... ?-)

[glennard]

Muf, This type of 'filled thermal' sensor was used extensively in the industrial business years ago. Because of the delicate nature and new solid state stuff, they are gonzo. But, they are OK if handled gently and will last and are pretty accurate.

[Cees Klumper]

Maybe the hand changed its position due to a restriction ("pinch") of the tube. The needle moves when the gas expands - the same effect would occur if the tube that the gas sits in, contracts, I suppose. So when you fiddled with the tube, you may have pinched it a little bit, causing the needle to move up. I suppose it is not inmpossible that, when you go to re-install it, the restriction gets less or clears up, and you will have to re-calibrate all over again ...

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Miloslav Maun]

It wasn't me who unscrewed it from the engine. It was the guys who have had removed the engine from the car. Then I came weeks later to remove the instruments from the dash. I have photos of the whole process, When I came to the car it was reading zero but then after my effort to remove it (and not paying too much attention to the fragile tube), it changed its position.
Well, OK, now I know how to adjust it. I can reset it once again if necessary :-)