Timing chain guides/rails - Exterior temperature gauges
 

I understand (e.g. from this site) that timing chains can last a long time on M103's. However, since I am not the original owner of my car (1991 W126 300SE), and to be on the safe side, I decided to have the timing chain changed at its current 127,500 miles.

I had also understood that it was advisable to change some timing chain guides/rails (and maybe sprockets, etc.) in the process, so I was surprised when only the chain and tensioner were replaced. When I inquired I was told that changing guides/rails is both unneeded and a "big job" on the M103's, and that it's in fact only needed on the V8's (i.e. M116's & M117's).

Changing subjects, my exterior temperature gauge currently either is blank or displays temperatures in the 130's. I was told that the whole dashboard must come out to look into the problem.

Opinions on any of the two subjects above?

Temperature Gauge
 

It is more likely you need to replace the sensor, NOT the display. This is about a one hour job you can do yourself. You can buy the part from Mercedesshop for about $50 or (if you are feeling a little more adventurous) you can buy a sensor without the connector from Radio Shack or other places and solder the new one on in place of the old one. Do a search for more info using a term like exterior temperature gauge or outside temperature gauge

I've tried the radio shack sensor and it doesn't work, it's very inaccurate (but it might tell you if the gauge is bad). I know enough about electronics to be dangerous, and here's the problem. All thermistors have a base reading (usually given at 72F) and a curve of resistance vs temperature or a formula, which is usually non-linear. There is no "standard" for this. I bought several thermistors from Mouser and I found two in parallel that are close from 60-100F. But still, I haven't found one that is really "right". If I get some spare dough I may buy the real thing, get set of measurements on it (not easy, but I can borrow a good temperature gauge), and then I can select the "correct" thermistor for others.