Coolant temperature sensor question.

[Frank de Kat]

>Date: Mon, 15 Jan 2001 14:11:10 -0500
>From: Huw Powell <audi at mediaone.net>
>Reply-To: one at humanspeakers.com
>Organization: HUMAN Speakers
>To: Bill Phelps <wphelps at rizzo.com>
>CC: "'quattro at audifans.com'" <quattro at audifans.com>
>Subject: Re: Coolant temperature sensor question.
>
>
>> I'm still diagnosing a cold running problem in my 87 4KCSQ. I checked the
>> resistance on the NTC Coolant Temp sensor (the bottom one on the upper rad
>> hose flange) and came up with about 8.7K ohms at @ 40 deg F. Bentley says
>> 2.5K ohms @ 68 deg. F.
>> 
>> Is 8.7K ohms too high for 40 deg F? The Bentley only says resistance "is
>> higher above 68F" or something similarly vague......
>
>sound like you need a new one.  since the resistance is supposed to rise
>with temperature (or is it?  that wouldn't be NTC it would be PTC) then
>yours being higher at lower temp would be bad.  Might want to read that
>spec again to be sure!  I thought there was a resistance spec for a
>lower temperature, too.  substituting a known value fixed resistor set
>to the "cold" spec can be a quickie way of checking if that is where the
>problem lies too.
>
>-- 
>Huw Powell
>
>http://www.humanspeakers.com
>
>http://www.humanthoughts.org
>
>--__--__--

For the NTC sensor, A higher ohm value makes the car run richer. (Try
unplugging the connector when the motor is cold! Try it when it's hot, and
it'll almost die, it runs so rich).
As long as the sensor is a high value when cold (value not all that
critical), cold starting should be OK. However, you want the hot value to
be of correct, so that the mixture is not running way too rich all the time.
( I just had mine out recently, and got about 3000 ohms cold, and around
250 ohms under the hottest  water from my kitchen tap)

Regards,




Frank de Kat 
fdekat at sentex.net   
Dundas, Ontario, Canada

Audi 4000CSq (x2 !)
http://www.sentex.net/~fdekat
(To see "The Rally Pictures")