Re: gauges

[D&L Walters <WALTEE@prodigy.net>]

Toby Erkson wrote:

> It's my understanding that the sensor needs to be at the spark plug -- at the
> head would give a different reading.  Put the sensor collar at the base of the
> spark plug and them screw in the spark plug.  That way the sensor will be right
> on top of the cylinder head/spark plug and give you a more accurate >reading.
Actually, the blurb that came with the gauges said that the #3 head stud
would be an "acceptable" site to mount the washer. It was my
understanding that there could be problems with mounting the washer
underneath the sparkplug as it could warp or dislodge and create a leak
from around the plug. It's funny how you can get diametric opinions from
different sources.  
> If your block is a FI one then you could get a sensor to screw in the >boss already there.
Nope, it isn't, you got me there.
> Also, I believe the general understanding for most gauges (except >those expensive ones) is to use them as an indicator and not as an >absolute.
I totally agree. It would be pretty darn impossible to acurately measure
the temperature chances in our engines in anything but a controlled
enviornment. The technology in todays engines is able to, but not in
20-30 year old VW engines. I think it is safe to say that these gauges
can really only be regarded as an "average sampling" of readings and not
much else. 
> The head stud may actually be hotter but that may not *really* matter >since your meter shows a dramatic difference from the norm.
I guess my question is just how hot is hot? My Notch with it's
semi-hopped up engine and ceramic coated exhaust and on Florida roads
never gets above 200 F. according to my VDO gauge, maybe 25 F. hotter
when the engine is just shut off.  I would think that the hottest point
within the combustion chamber would be at the point of ignition, the
sparkplug. The head stud would be within the path that the heat takes as
it is drawn towards the cooling fins. The problem is that the VDO gauge
range is from 100 F. to 600 F. so 200 F. is at the extreme end of the
scale, where gauges tend to be their least accurate. I suppose that the
thing to do in a perfect world would be to get a pyrometer, take
readings across the scale and then adjust my readings to reflect them. I
don't think that VW ever put out any logistics on the correct engine
temps, and if they did it would be pretty heavy to cover every  type
engine, and size, and application. I guess all this really isn't an
exact science, now is it?
David Walters
'73 1600 L Notch
S. FL, USA