Replace the thermostat. Even new ones may not work properly.
"2forgetmenot" > wrote in message
lkaboutautos.com...
> Let me state my problem again with this.
> Everyday I warm my car up for 5-15 minutes before driving. After
> approximately 2-5 minutes of driving the thermostat needle starts to
> slowly drop down to cold, the car down shifts by itself and the engine
> roars loudly becaue the RPM's are so high when the transmission down
> shifts. I took my 94 Mazda Miata to a Mazda dealer. They first said the
> thermostat was getting stuck. They checked that and that was not the
> problem. Then they did some type of engine cleaning (so they said)which
> cost me $74. The final analysis was I probably had a bent valve, which
> would have cost me $750 to repair. I elected not to repair, becaue this
> was an educated guess, but I wasn't interested in taking a stab in the
> dark for $750. Any ideas?
>