1986 4000cs AC

Huw Powell audi at humanspeakers.com
Sat Jun 19 22:55:39 EDT 2004

>> I am in Las vegas and use my car for my job as a courier. The real 
>> serious heat has yet to show up so I am working on keeping the car 
>> cool as well as myself once it does. I drive anywhere between 120-150 
>> miles a day. Most of it freeway miles.
>> A few questions
>> 1 ) My radiator fan is getting twitchy on me. I get a replacement on 
>> monday. Should I install a switch to keep the fan on when I am driving 
>> all the time ? Or let the rad. fan switch do it`s job ?
> Leave it with the switch- running too cold will increase cylinder wear 
> and decrease mileage.

Agreed... at highway speed airflow alone should be plenty to keep the 
coolant below "fan-on" temps.

> When you have the replacement installed, consider installing a fuseable 
> link.  It was added to cars after 1989 or so, to avoid harness/battery 
> meltdown in the event of fan failure.  The links are available in wire 
> form or you can get the parts installed into the 100/200's.

Although it ispossible to move one wire in the fuse box to properly 
protect the rad fan, a fusible link is probably easier to "add."  But 
don't use the one for the type 44, it's much higher amperage than you 
need.  Try a 25A one.

>> 2 ) If not enough air is pulled through with a  'stock fan' is there a 
>> more efficient replacement fan to use ? This also helps cool the AC 
>> for me ,correct ?

Yes, the AC condenser is right in front of the radiator.  The stock fan 
*should* be enough... are you seeing elevated temps or continuous 
running at low speeds?

>> 3 ) Just a thought ,would an oil cooler work to keep everything cool ? 
>> Has anyone added an oil cooler to their Audi ?
> Oil coolers are stock on all I-5 turbo engines out of necessity; they 
> make a lot more power and dump a lot more heat into the oil courtesy the 
> turbocharger.  A friend's 4000 which was on-track at Lime Rock in 
> intense heat only hit maybe 120, I think, on the digital bar 
> gauge....and it was spending a good bit of the time at very high RPM and 
> load.  Given yours is seeing neither...

I can get my coupe up to 150 C by redlining it in third for a bit pretty 
easily (and that's about 85 mph with the tall gears).  But even doing 
that, I see no coolant temp build up.  But that is without AC even being 
on the car.

Bottom line, I'd say what matters is where you see your coolant temps 
go.  If they are getting worrisome, an oil cooler *might* help get rid 
of some extra heat before it gets to the coolant.  At least you can use 
the bits Audi used on the turbo engines to "engineer" it.

I do think that with everything clean and working right, your car should 
be able to "keep its cool," even with that desert city calling its name.

Huw Powell



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