5kcst thermo sensor Q

[Steve Sherman]

Ti:

Thanks. I have not ruled everything out yet, but I am slowly going thru the
list.  I have replaced the radiator (was leaking at the seam anyhow), and the
fan/motor are only 1 yr old.  2speed fan sensor in the rad was replaced too.
Tomorrow is the thermostat and lower rad hose. Perhaps the thermostat will fix
it.  But I am trying to line my ducks up in case this does not...

I am coming to the conclusion that it is not the rad/fan/sensor system, as
there is no flow problem there (checked the rad before install), fan works
well, and sensor is new.  And when the fan does come on it seems to cool fairly
quickly and shut off.  At first I thought that was the sensor being flakey and
not running the fan enough.  However now I am thinking it is a lack of flow of
hot coolant from the block to the radiator.

That would seem to be either the thermostat or the water pump.  (or I suppose a
possible physical blockage somewhere in the coolant passages but I would think
that's rare).  With luck it will just be a thermostat that does not open all
the way....

The sensor stuff is just because I do not really think my engine is "that"
hot.  I don't have a IR reading meter to be sure, but the engine is not smoking
hot and does not smell hot.  And so while I don't think everything is just fine
and it's all bad sensors, I do think that the sensors might be reading high....

Steve







Ti Kan wrote:

> Steve Sherman writes:
> > I'm still trying to track down my "overheating" issue with my 87 5KTQW,
> > and started thinking about a new line of investigation...  Perhaps my
> > engine is not overheating (it never gets real hot) but rather it is a
> > sensor issue.
>
> How did you determine that it's not a bad thermostat or clogged radiator,
> but a sensor problem?
>
> > The symptoms I see are temp gauge running at 3/4 level, and when stuck
> > in traffic on hot days, or going slowly up a steep hill on hot days, the
> > flashing triangle with a thermometer will come on in the dash.  I was
> > wondering what sensor(s) run the dash temp gauge and set off the temp
> > warning symbol?  are they the same one?  Perhaps I should replace it?
>
> Both the coolant temp gauge and the auto-check overtemp warning sensor
> are the "multi-function" thermal sensor located on the bottom of the
> top radiator hose flange on your cylinder head.  However, the two functions
> are (I believe) separate, and if your gauge is reading high *and* you get
> the overtemp warning, then chances are it *is* running too hot.
>
> -Ti
> 2003 A4 1.8T multitronic (soon)
> 2001 S4 2.7T
> 1984 5000S turbo
> 1980 4000 2.0
> --
>     ///  Ti Kan                Vorsprung durch Technik
>    ///   AMB Laboratories, Sunnyvale, CA. USA
>   ///    ti at amb.org
>  //////  http://www.amb.org/ti/
> ///