Under Reading coolant gauge on I5 100

[Huw Powell]

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/