The sender for the gauge sits on the engine right? The coolant in the lines and
the radiator is colder than the coolant in the engine. You speed up the
circulation, the cold coolant comes to the engine before the temp levels out.
Seems to make sense.

PerL
87 Syncro 112i

KENWILFY@AOL.COM wrote:

> Had a weird thing happen while checking out a customer's van today.  Ran the
> van up to temperature and let it idle.  It went slowly up to around 3/4 of
> the gauge before the fan came on.  I put in a new switch that now comes on
> right after the needle passes the LED (better).  However the van did
> something weird when I was trying to warm it up after replacing the switch.
> The needle was at the middle (LED) and I wanted it to heat up faster so I
> revved the motor up to around 2500 rpms and held it there.  As I watched the
> needle it actually went down in temp 1/8 of the gauge and then started back
> up again!  I had never seen this before (usually they hold steady and slowly
> climb).  Any ideas on this one?  Just normal operation and I never noticed it
> before (possible)?
> The old fan switch might have been good but the part of it that sticks into
> the rad was covered with goop (Bar's Leak?) and this could have had an
> insulating effect on the sender.
> I was wondering if the inside of the radiator is coated with goop if this
> could be messing up its heat transfer properties?  Any ideas?
>
> Thanks,
> Ken Wilford
> http://www.vanagain.com
> John 3:16
> Phone: (856)-765-1583
> Shop:   (856)-327-0027
> Fax:     (856)-327-2242