Under Reading coolant gauge on I5 100 (happy ending)

[rob hod]

    Well, I tested the deflection of the temp. gauge with the suggested
resistances and it was way out. Seeing as a few instrument cluster lights
were burnt out I took the cluster out for a look.

    I realised that the temp gauge has a calibration spindle, so after
removing the locking gunk I tweaked it up a bit. I don't know what the
Bentley says but the Haynes makes no mention of it being adjustable.
    Then I put in a new t-stat. Checking it against the old one in a pan of
water I found the old one was opening earlier than the new but not by much.

    Net result was very pleasing, - car warms up quicker and holds a nice
temperature for interior heating and needle sits firmly below the mid point
on the gauge. I'm happy. Roll on winter.

    Thanks for everyones help.

rob
----- Original Message -----
From: Huw Powell <audi at mediaone.net>
To: rob hod <rob3 at hod3.fsnet.co.uk>
Cc: <quattro at audifans.com>
Sent: Monday, November 05, 2001 12:26 AM
Subject: Re: Under Reading coolant gauge on I5 100


> Everything you say sounds accurate.  It seems like you have diagnosed
> either poor wiring or a faulty gauge or regulator (gauge volt reg that
> is), since shorting that wire should peg the gauge.  Of course I'm
> looking at the wrong year in a copied Bentley and the wire should be
> brown/yellow according to it.  It shows no brown/black wire though.
>
> the pin in question is the upper right when you look into the wiring
> connector with the little "V" indent at the bottom.
>
> 660 ohms should put it at about 1/3 scale, 50 ohms at about 2/3, where
> it says "H".  How good is that ground you are making?
>
> rob hod wrote:
> >
> >     Wonder if anyone can help me out on this. Patient is an '88 100 with
2
> > Litre I5 engine (RT).
> >
> >     The problem is that the temp gauge is under reading. I have a sneaky
> > suspicion the thermostat has been removed as the car generally runs
cool,
> > I'll be checking this next weekend.  However there's no doubt that the
gauge
> > reads under, for example the car is running up to a reasonable temp.  in
> > summer but rarely reads more than 1/4, and for further proof the
radiator
> > fan cuts in with the temp gauge reading around 1/3rd f.s.d.
> >
> >     Now the specifics of my query are this, The wiring diagram mentions
an
> > 'electronic thermoswitch, and the wiring on the car suggests that this
is a
> > brass fitting with a four pin electrical connection under the upper rad
hose
> > connection to the head.  Before I bought the car I think this sender was
> > replaced as I have an invoice for Pn 034 919 369C "Temp sender" I wonder
if
> > a slightly wrong part was used? If I take a lead from the brown/black
wire
> > on the socket and earth it with the engine off but the ignition on I get
a
> > gauge reading of around 2/3rds. Anyone know if this part is indeed the
> > 'electronic thermoswitch mentioned in the manual?
> >
> > I have a theory that I may get a slightly higher reading with the engine
> > running, but presumeably the voltage stabiliser should limit that to a
fair
> > extent.
> >
> >     In addition there is a small sensor fitted to the top of the hose
outlet
> > fitting which also has a brown/black wire going to it.
> >     Anyone know if this is the 'overheat' sensor or the actual gauge
sensor
> > ?
> >
> >     By the way the fuel gauge appears to be working and calibrated
properly.
> >
> >     Thanks in advance
> >
> >     Rob Hod
>
> --
> Huw Powell
>
> http://www.humanspeakers.com/audi/
>
> http://www.humanthoughts.org/
>