<VV> valve seats - Head Temps

[Dave Keillor]

I know what the manufacturer considered too high -- 575F for AC, turbo, and
140hp cars; 525F for all others.  At least this is where the snap switch is
supposed to close.  Why the difference?  I doubt it was because the AC,
turbo, and 140hp cars had superior heads.  It was almost certainly because
those cars ran significantly hotter, so the switch point was moved higher
to avoid undue driver angst.  Personally, I consider even 525F to be too
high, but it's consistent with the temp warning lights of water pumpers of
the era where the red light informed you that your radiator was boiling.

As far as accuracy of the Corsa gauge, I suspect it was reasonably accurate
(within 50 degrees) when the car was new.  However, measuring head
temperatures in an air cooled engine with a thermistor is at or beyond the
temperature where thermistors are stable and reliable.  I would never trust
a thermistor-based gauge in an older car.  On the other hand, based on some
calibration work I've done on a limited sample of uncompensated,
thermocouple-based gauges, I don't trust them much, either.  However, they
are likely to be much more stable over time than a thermistor-based gauge.

Dave Keillor

On Thu, May 10, 2012 at 9:02 AM, corvairduval at cox.net
<corvairduval at cox.net>wrote:

> I considered 550 on my 64 Spyder gauge too high. 600+ was seen early in my
> ownership. 500 on a normal summer day interstate speed was a typical
> reading.
>
> Of course the heads were dropping vavle seats regularly. And why it is off
> the road currently. It is a 145 cu in YR engine.
>
> Most miles were before the vast knowledge of head deflashing, etc. we have
> now on the internet discussion boards and forums. There is no RED zone on
> the factory gauge, so what is too hot? I know many Spyder owners who
> experienced similar readings. Corsa owners however, always had lower
> readings. Maybe due to most being normally asperated 140s instead of all
> turbos like Spyders?
>
> And, how accurate was my gauge?
>
> Frank DuVal
>
>
>