1989 Bird speedometer reads about 20% faster

[fostersservus]

When driving the speedometer reads too fast by about 20% or higher, at 30 mph it reads 35, at 40 it reads 50, at 60 it reads 75. Also the temp gauge reads very low, barely raised above the bottom when the car is fully warmed up, replaced the sending unit but that didn't fix it.

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[mcm51]

Three thoughts on the incorrect speedo reading, diff. has been changed, instrument cluster is faulty, tire size is way off.........thoughts on temp reading, temp sensor with one wire going to it is faulty, thermostat stuck wide open or missing completely.............

 

[mcm51]

Oops, forgot one on the speedo reading, VSS, vehicle speed sensor faulty...............

 

[fostersservus]

Three thoughts on the incorrect speedo reading, diff. has been changed, instrument cluster is faulty, tire size is way off.........thoughts on temp reading, temp sensor with one wire going to it is faulty, thermostat stuck wide open or missing completely.............

Thought that the thermostat might be faulty as in wide open but figured when the car was fully heated up that the gauge would move up closer to mid range but it stays almost at the cold, it used to work then it didn't so replaced sending unit and it seemed to work better for awhile, replaced sensor again because of low reading and now it stays very low. Will look at the thermostat next..

 

[fostersservus]

Tires are correct size per owner's manual so pretty much ruled that out although some taller tires might help, maybe a bad ground for the gauges (the gas gauge is also unreliable), will look into VSS next. Was thinking of taking the needle off and pushing it back on about 5 mph lower. This previously granny owned car now has 83,000 miles on it but seems like it tacks the miles on about 20% faster than it should.