I need some ideas. It's just gotten cold here in Texas, and I've started using the heater. Over the last couple of days, when I put on the heat, the blower came on and blew cold air. The coolant temperature gauge would rise to about 100 C. Then all of the sudden, heat would blow and the coolant temp returns to normal. Today however, even with the temperature set to MAX, cold air only, and the coolant temp went into the red. The coolant level light has not come on, and I had just topped it off not too long ago. I'm not sure what's going on. Any ideas? Thanks!

Don

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Don Drake

1990 300E 125k Miles
1994 S420 100k Miles

sounds like your aux fans are not working. they should kick in at around 110...

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joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
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Sounds like a stiky thermostat.

Does this happen only when you use the heater?

Aux fans are working well, and yes it only happens when I use the heater. As I said, if the heater does begin to blow hot air, the coolant temperature rapidly returns to normal. It seems as if the heater somehow blocks the flow of the entire system when turned on?

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Don Drake

1990 300E 125k Miles
1994 S420 100k Miles

Does the aux. water pump to the heater check out OK? Other threads, including http://www.peachparts.com/shopforum/showthread.php?threadid=15038&highlight=auxiliary+water+pump
indicate that the monovalve may be going bad, or that the pushbutton control unit is marginal. apparently a failing aux. water pump can 'use the pushbutton unit as a fuse' and kill it. If it is the aux water pump, it should be a relatively easy diagnosis. The monovalve or a combination pump/pushbutton problem could be more of a problem. Good luck!

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

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