Re: Rad fan dosen't run after engine off !

[steveb@newkla.kla.com (Steven Buchholz)]

I said ....
> > it on non-turbocharged cars of any vintage.  From what I have heard, al-
> > though other manufacturers use water-cooled turbo jackets Audi may be the
> > only manufacturer that has such a cooling system on their stock turbos.
> 
... to which Arun replied ...
> 
> 	My '85 5KT doesn't have the water-cooled turbo (engine code KH
> 	doesn't have it, MC does), but the fan runs after shutdown. So
> 	does the injector fan, when it's really hot. What's more, my
> 	'80 Fiesta used to do it, and my '92 Accord sometimes does (both
> 	as normally aspirated as they come, of course).
> 
> 	My turbo-diesel Volvo 740 didn't do it, but then it would have
> 	had to start up the engine to do so :-)
> 
> 	Anyway, maybe there's more to it than meets the eye: I find
> 	it hard to believe that all these different manufacturers would
> 	find it expedient to build in a feature which is useless, especially
> 	one that probably costs money to put in and has zero customer
> 	visibility (audibility?).

Yes, you are right that many manufacturers that have turbo and non-turbo
cars do run the rad cooling fan after shutdown for some reason.  I would
imagine that convection will continue to cycle some water through, but I
wonder how effective it really is.  On the '78 Fox the fan switch was 
mounted on the radiator itself, so once the rad was sufficiently cool 
the fan would shut off.  I guess that I am dubious that it performs any
real function and that it is convenient to have it work the way it does
and should not cause significant drain on the battery in normal situa-
tions.  Being a Goldi owner (x3) I know that Murphy and Vorsprung will
conspire to make "should not" a lie ;-)  

The injector cooling fan on the turbocharged motors does serve a purpose 
after the engine is shut down however.  The intent of the injector cooling 
fan is to minimize the probability that the fuel lines and injector will 
get so hot that vapor lock will occur and improve hot starting performance.  

I was not clear on my major point though.  Although many manufacturers 
allow the rad cooling fan to run when the engine is off, and some use 
water-jacketed turbos, I am aware of no others that have an electrical 
water pump to cool the turbo after the engine is shut down.  There prob-
ably is someone else out there that does so, I'm just not aware of it.

Steve Buchholz
s_buchho@kla.com