The same thing happens to me - I hope it is normal.
Here's my theory:
The ability to maintain 180 is governed by the limitations of the ENTIRE cooling
system, not just the thermostat. Even though the t-stat opens at 180, the rest
of the cooling system cannot keep things that cool when it is extremely hot out
and little air is passing through the radiator (city driving.) When you drive
on the highway, the radiator can do it's job better (it is no longer the
"weakest link") and the temp drops.
"Panoli, Robert" wrote:
> With the OEM thermostat, the temperature gauge was pretty solid at 195 no
> matter what the outside temperature was or type of driving (highway or city,
> AC on or off). Now since I installed the 180 deg thermostat the gauge seems
> to fluctuate a lot (especially if its hot out driving in city traffic with
> the AC on, the gauge reads close to 200). As long as its cool out the gauge
> reads closer to the 180 mark like its suppose to. Is this normal? I checked
> the coolant level and it was O.K.
>
> Bob
> 99 Sport 5.2L 5-spd
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