Mercedes Benz repair: 1989 300TE Wagon ME/BE - Thermostat, gagues, engine temperature

Question
I must change the thermostat in the wagon? Can you give me the steps to do this? or recommend a good repair book with pictures? This is my real name. Car over heats at stops, but does not  register overheat on dash. Not sure if dash gagues are working will check.

Answer
Best guess:
The engine temperature sensor or wire are damaged.

Thermostat change:
First picture #32.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124090%5F15U&M=103%2E98%5F505&GA=722...

If this is happening with the A/C on = the aux cooling fan circuit failed.