Why does my speedometer run about %15 fast first thing in the morning. The odometer seems to still be correct. After the car warms up, the speedometer goes back to normal.
its all the extra hp from dense cold air.Why does my speedometer run about %15 fast first thing in the morning. The odometer seems to still be correct. After the car warms up, the speedometer goes back to normal.
Possibly the cable expands when it gets warmer but thats a real stretch
Mine does this aswell. So it's not the cable but a part in the dash?
1991notchbackLX said:I hope you guys aren't relying on the stock tachometer for accurate RPM readings...
Very good info. Since I don't really want to change the speedo head, I'll just live with it.How the speedometer works:
The indicator pointer has no direct connection to the speedo cable. It uses a drum with magnets on it to couple to the pointer. The drum turns and tries to twist the circular steel disk that is mounted on the pointer spindle. The magnetic force is all that connects the drum to the circular disk. There is very little clearance between the disk and drum, only a few thousands of an inch.
A Google search turnd up this gem::
SPEEDOMETER-MECHANICAL (ANALOG)-INDICATES HIGH SPEED AT LOW AMBIENT TEMPERATURES (ABOUT 20 DEGREES F OR -7 DEGREES C OR BELOW)- VEHICLES BUILT AFTER 4/1/90
FORD:
1990-92 ESCORT, MUSTANG, TAURUS, TEMPO
LINCOLN-MERCURY:
1990-92 SABLE, TOPAZ, TRACER
LIGHT TRUCK:
1990-91 AEROSTAR, BRONCO, ECONOLINE, F-150-350 SERIES
1990-92 RANGER
1991-92 EXPLORER
ISSUE:
Mechanical speedometers may indicate higher than actual vehicle speed at low ambient temperatures (about 20~ F or -7~ C or below). This occurs because of insufficient lubrication at lower temperatures. The speedometer will indicate speed correctly after the vehicle warms up.
Replace the speedometer head with a service speedometer assembly. Speedometer part numbers are identified in the Parts Block/Application Chart. Refer to the appropriate Service Manual for removal and installation details."
Quted from said TSB on AllData