Changing the coolant in a 5k is a pita plus long rant

Al Streicher streichea001 at
Thu May 24 10:11:27 EDT 2007

If you open the heater valve, have the engine hot so the thermostat is wide 
open, wouldn't you remove a bigger percentage of fluid, when you pull the 
lower radiator hose? You will still need a few cycles of distilled water 
flushes, then add 100% anti-freeze and balance out with distilled water.

I think you could back flush the system through one of the heater hoses, but 
that may also be a pita. If you had an old heater hose you could get the 
valve assembly for back flushing at a Flaps, not sure about the correct 
diameter, etc.

----- Original Message ----- 
From: "DeWitt Harrison" <six-rs at>
To: "Quattro List" <quattro at>
Sent: Wednesday, May 23, 2007 4:51 PM
Subject: Changing the coolant in a 5k is a pita plus long rant

> Not all that long ago, there was some discussion about the difficulty
> of completely replacing the coolant in an MC engined car. I may
> have missed some stuff because I turned off mail delivery during an
> extended absence. Sorry if this covers old ground.
> It had been observed by a q-lister that draining the old coolant per
> the book, i.e. disconnecting the lower radiator hose from the thermostat
> housing, did not seem to empty the system. I have just gone through the
> exercise of renewing my coolant and have found it to be an exercise
> in frustration. (Note: Short of pulling the thermostat itself, one way to
> remove more coolant from the system is to either remove or somehow
> introduce a break in the seal of the heater return hose which connects to
> the
> block on the engine side of the thermostat, just adjacent to the radiator
> hose mentioned above. Clearly, pulling the thermostat altogether would
> be the most effective method.)
> [Side note: in part, the coolant change was motivated by the desire to
> get away from Prestone's orange, long term' crap, which was
> problematic from day one, and get back to the good old green stuff.
> If the question of which is the best antifreeze is your issue, please 
> start
> a different thread. That's got nothing to do with this email.]
> When I used the method described and carefully measured the volume
> of coolant removed, I found that 9 pints would be released. This is out of
> a total coolant volume of 18.8 pints. In other words, following the book
> method apparently drains only about 54% of the total coolant volume,
> leaving 46% of the old fluid or 7.7 pints of the stuff. I don't know where
> the old coolant is stored but it is pretty obvious that Audi could have
> designed a more efficient coolant drain point. (On my old 2002, there
> was a secondary drain plug at the right-hand, lower corner of the engine
> block - the lowest point in the system, duh.)
> Now I assume there must be an efficient method for removing all the old
> coolant but if you foolishly do as I have done and flushed by repeatedly
> draining and refilling by disconnecting those hoses, you will have to go
> through several cycles to do a good job. Each drain and refill cycle will
> replace 54% of the coolant. If you do this "N" times, you will have 
> reduced
> the amount of remaining, old coolant by (0.46)^N. As an example, 
> 'flushing'
> twice will leave 0.46 x 0.46 = .21, or 21%, of the original fluid. To get
> the
> remaining old coolant percentage below 5%, you would have to repeat the
> process 4 times. I've gone through 5 cycles using distilled water (2% old
> stuff remaining) and I can still see the cloudy residue of the old 
> coolant.
> This brings up the old trade-off of  "total dissatisfaction" vs. "how many
> hours do I devote to this?"
> There must be a better way. Would someone please enlighten me?
> I suppose there must be a way to stick a garden hose into an open
> connection and blow all of the old shit out. (That would still leave 
> nearly
> 8 pints of "garden hose water" sitting in the system as far as I can tell.
> Not a great thing if you believe the only water in the system should be
> distilled water.)
> A related point is how to properly fill the system with the correct
> mix of water and antifreeze. You can't simply poor in a 50/50 premix
> of water and antifreeze because there will always be some 8 pints
> of 'whatever' still sitting there. Therefore, I submit that the correct
> thing to do after this sort of flushing procedure -- this assumes there
> are 8 pints or more of distilled water in the system as a result of all
> these flushing cycles -- is to follow the last cycle of coolant dumping
> by adding the theoretically correct amount of 100% antifreeze and
> then topping off with distilled water as required to bring up the coolant
> level to the mark. The Bentley and the Audi owners manual both
> claim that my system should contain 8.4 pints (a bit more than one
> gallon) of antifreeze and 8.4 pints of water to have a 50/50 mix. So
> I poured in the gallon and topped things off with distilled water as
> required meaning "not much." I have not yet measured the mix with a
> hygrometer but I will report the result when I have.
> Meanwhile, I am just beginning to adjust to an Audi World which no
> longer admits to the existence of my car. All the CIS fuel hoses any
> many, many other parts where dropped from the Audi parts system in
> 2005. Most parts for the car are actually now NLA. So much for
> Audi's support for their classic cars. (BMW, Mercedes and Porsche
> all have programs specifically aimed at supporting the classic cars.
> I have had no problem with replacement parts for my 1987 BMW
> 635CSi. Expensive? Yes. Available? Yes!!) Sadly, it's almost
> time to put the old girl up on blocks behind the barn.
> Go figure why I would never in a million years consider buying a new
> Audi. I am constantly amazed how the corporation can decide to
> blow off the older cars -- I have also observed that you poor mother
> f.....ers who own '91 200s or ur S4/S6s are nearly SOL when it comes
> to factory only parts such as bumper covers -- and expect repeat
> business. List price for a new brake master cylinder for an Ur-S4/S6 is
> well over $600. But it is STILL AVAILABLE you lucky bast..ds!
> Not much else is.
> Sooner or later the automotive public will become aware of  Audi's
> 'car-as-appliance' mentality and send the company into the same
> tailspin into hell that Ford and Chrysler are now experiencing.
> DeWitt Harrison
> '88 5000CS
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