[V6-12v] Radiator Fans not switching in correctly...

[James Whitehouse]

Do you know how the 1st stage fan relay fits in to this?

Cheers,
James

> -----Original Message-----
> From: Tom Christiansen [mailto:tomchr at gmail.com]
> Sent: 09 September 2006 22:09
> To: James Whitehouse
> Cc: V6-12v at audifans.com
> Subject: Re: [V6-12v] Radiator Fans not switching in correctly...
> 
> James,
> 
> It's a simple switched circuit. There's a thermo switch in the
> radiator with two switches in it. One for low speed, one for full
> speed. When the temperature in the radiator reaches the trip point for
> the "low" switch, the fans get power from the battery through the
> resistor pack, through the thermo switch. When the "high" temperature
> is reached, the second switch in the thermo switch kicks in and shorts
> out the resistor pack. There's nothing to it. There are no timers or
> any other funkyness (that was the case on the 4000/5000 models of the
> 80'ies, but it does not exist on my 1994 90S). The fans are controlled
> by the temperature of the water in the radiator only. The reason the
> fans stay on for a while is that the thermo switch has some built-in
> hysteresis. Otherwise the fans would kick in, turn off, kick in, turn
> off... at a rather rapid rate.
> 
> Re expansion tank cap: Mine ran about $5. I'd just get a new one. I
> don't know at which condition the valve in the cap is supposed to
> open, but I do know that the pressure has to exceed 15 psi (about 1
> ATM) for it to happen.
> 
> Tom
> 
> On 9/7/06, James Whitehouse <james_whitehouse1 at yahoo.co.uk> wrote:
> > From testing this morning, the rad seems to heat up fully when getting
> up to
> > temp from cold, then after the fans switch in once, it develops a cold
> spot
> > near the top. Does that indicate a thermostat issue rather than a rad?
> >
> >
> >
> > The thing is that none of the cold spots are near the bottom where the
> > thermo-switch is, so I still don't understand why the fans aren't on
> long
> > enough to cool the engine down. What controls how long the fans run for?
> Is
> > it a relay, or the actual radiator thermo-switch itself?
> 
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