Hey guys I have a 1984 300SD, Im having a problem with the heat. The heat gets warm but not as warm as i think i should. The engine temp stays at about 60c degrees during normal driving but if i drive it on the freeway or kinda hard it gets up to about 80c degrees. When its at 60c degrees the heat does not work very well. Could it be that the engine is running to cool? If this is the case what can i do to make it run warmer?
thanks

Your engine should be running at about 80C. Your thermostat is defective. Replace the unit (include a new oring). If you would like you can test your old thermostat. It is also a good idea to test the new thermostat.
Place it is a pan of water. Insert a thermometer in the water. Bring it to a boil. As the water approaches 80C the thermostat should be fully open. If it fully opens at a lower temp it is defective. Allow it to cool and install the good thermostat.

If the thermostat tests normal then it could be other things. If you get the engine to operate at 80C and heat is still weak then we will look at the mono valve. They can and often do go bad.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
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1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car