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Old 02-20-2002, 10:44 AM
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Join Date: Nov 2000
Posts: 168
Aux. water pump, What's it's purpose?

Could someone please tell me what the purpose of the auxillary water pump is? When should it come on? What if it doesn't? Any help would be appreciated. thanks, andy
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Old 02-20-2002, 12:43 PM
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Join Date: Aug 2001
Location: Atlanta, GA
Posts: 5,514
It was my understanding that the aux. water pump is supposed to ensure that coolant gets to the heater core at lower RPMs, so that you have heat when the car is idling.

1979 300 SD
350,000 miles
1982 300D-gone---sold to a buddy
1985 300TD
270,000 miles
1994 E320
not my favorite, but the wife wanted it
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Old 02-20-2002, 02:49 PM
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Join Date: Sep 2001
Location: Lathrup Village, Michigan
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That is also my understanding. At idle, waterflow is not sufficiant. In my '75 300D, which does not have an aux pump, I used to rev the engine every once and a while to get heat out of vents while my wife and I parked at the ski slopes and watched the skiers at night.
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

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Old 02-20-2002, 03:22 PM
Fimum Fit
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Trust the two Mikes

The Florida fellow must be confused by the many front-drive cars which have a circuit to turn on the electric cooling fan when the ignition is off if underhood temperatures create a possibility of vapor lock.
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Old 02-20-2002, 05:21 PM
Fimum Fit
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Thank You, TK, I leaned something new,

at least about 124 cars -- I've got a 123 Diesel ('85 300TD) and I wonder if it's true of them too (mine has never been over 85 on the temp gauge)? I'll have to try to make my new CD manual work this weekend and find out, but I've been having trouble getting it up and running.
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Old 02-20-2002, 05:26 PM
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To: Fimum Fit - if your CD is browser based like mine. A little hint - mine worked erratically or not at all. To make long story short - read the readme text on the CD. I already had Acrobat 3.0 installed when I installed Acrobat 4.o off the cd. They conflicted. Removed both versions and re-installed Acrobat 4.0 from cd and all is well.
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Old 02-21-2002, 07:41 AM
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Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
The other issue is that if your aux water pump draws too much current (I don't remember the specs), it will eventually fry your pushbutton climate control panel. If you think yours is not working properly, it would be good to get those specs and test the current draw to avoid collateral damage.
'93 400E
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