How much amperage can an alternator support? no really...

john at john at
Mon Feb 4 18:54:34 PST 2008

I  work on Audis and VWs for a living (35 years this month!), and I 
spend a significant portion of my work week doing driveabilty and 
emissions testing prep.  That's the real world, and your theory doesn't 
wash.  If the fan's on all the time, 90% of the time it won't pass smog. 
It's just like having a thermostat stuck open.  As for the old cars 
running the fan all the time, those old cars ran carbs, and they were 
unbelievably dirty, even when the chokes were working properly.  They 
mostly got abysmal mileage (who cared, gas was a quarter?).  BTW, 
temperature management is a big deal now, that's why they shroud the new 
engines.  Gotta go, dinner awaits!  John

LL - NY wrote:
> Actually, the thermostat should prevent the engine from running cold. 
> FWIW, most 'merican and other vehicles with mechanical fans used to 
> run their fans all of the time. It wasn't until the '74 fuel crisis 
> before thermo clutches to decouple the mechanical fans became 
> commonplace.
> LL - NY
> On 2/4/08, *John Larson* <westcoast at 
> <mailto:westcoast at>> wrote:
>     On 2/4/08, Vittorio Bares <Vittorio.Bares at
>     <mailto:Vittorio.Bares at>> wrote:
>     >>
>     >> Thanks - this is good info, and encouraging.
>     >>
>     >> My cooling fan is on a manual switch and I typically run it
>     always-on
>     >> (eliminates one more point of failure in the temp-switch). Any
>     idea what
>     >> amperage that draws?
>     >
>     Running the fan all the time is a less-than-good idea.  The engine
>     will
>     never get up to correct operating temperature and tend to burn
>     substantially more fuel over any given period of time than an engine
>     running at the prescribed engine temperature.  Audi, and all other car
>     manufacturers go to great lengths to achieve a stable temperature
>     environment for their engines, mostly for efficiency and
>     emissions, but
>     also for optimum power from their engines.  You're essentially running
>     in warm up mode all the time.  As for the response stating that
>     the temp
>     switch isn't meant to carry a high current load over an extended
>     period,
>     I think that's bull.  The switch operates the fan relay(s) and doesn't
>     carry all that much current.  I use them in air cooled applications to
>     operate oil cooler fans, and they run for hours under high heat
>     situations all the time.  Back in the days of the 100LS, Fox, and
>     early
>     Rabbit/Jettas, we saw quite a few fan switch failures, and sold a
>     lot of
>     them.  I doubt I sell 2 a year now, except for the ones we install
>     when
>     we change the radiator.  Not much of a failure point.  In fact, I
>     probably sell more fans than switches.
>     John
>     _______________________________________________
>     quattro mailing list
>     quattro at <mailto:quattro at>
>     ---
>     Watch this space for ads :)

More information about the quattro mailing list