[V8] Re: cold weather killing gas mileage (AHA!!!)

dsaad at icehouse.net dsaad at icehouse.net
Mon May 2 10:37:25 EDT 2005

I does not take much of a leak around the thermostat to really kill mileage in
sub-freezing weather. If you think about it a little, the cooling system in
effect is trying to keep the radiator at 97C (its a side effect of keeping the
motor at 97C). It can't of course so if you have a slow or sticky t-stat, it
will shut untill the motor heats up - then it opens too much - letting in a
deluge of really cold water. The thermal shock alone is not good, and the ECU
will dutifully notice the operating temp is too cold and put you back in cold
enrichment mode. If you can see the needle swing back and forth then you have
something like this going on.

This is one reason there is a tiny bypass hole in the thermostat. It will allow
some cold water to pass - hopefully keeping the t-stat more closed when it is
cold, and prevent the wild swing.

That brings up a point - did your new t-stat have the by-pass valve? (the little
steel ball in a cage) and is it installed properly? You can often install the
t-stat backwards if you are not careful.


Quoting Ingo Rautenberg <i.rautenberg at waratap.com>:

> You guys have me thinking.  This morning I watched my temp gauge and at 42°F
> it took (mixed city/hwy) over 20 minutes to get to operating temp.  Over
> twice as long as I would think.  And thermostat  was replaced less than 20k
> ago...
> Ingo
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.857 / Virus Database: 584 - Release Date: 2/10/2005
> _______________________________________________
> Audifans V8 mailing list
> Send posts to: mailto:V8 at audifans.com
> Manage your list connection: http://www.audifans.com/mailman/listinfo/v8
> Have an Audi V8 question?  Check the Audifans Knowledgebase!
> http://www.audi-quattro.org/cgi-bin/twiki/view/Audi/V8
> Have a V8 answer? ... Please help others by adding to the KB ... all
> contributions welcome!

More information about the V8 mailing list