Tach not accurate when car is hot

[ahetzel]

OK, I have an early MK1 with an original tach that has been working fine. A few days ago I noticed that the tach is accurate when going to an event. After parking and sitting in the sun that tach read 500+ RPM high when driving home. The problem goes away the next time the car is driven cold out of the garage. Any ideas?

 

[0neoffive]

Heat Stroke

OK, I have an early MK1 with an original tach that has been working fine. A few days ago I noticed that the tach is accurate when going to an event. After parking and sitting in the sun that tach read 500+ RPM high when driving home. The problem goes away the next time the car is driven cold out of the garage. Any ideas?

Just drive in the winter . . . . . .

 

[ahetzel]

You did notice that live in Chicago?

 

[0neoffive]

Can't Count Right

Assuming you have a stock tach & ignition system, it could be time to have the instrument gone thru. Since these critters count revs by pulse induction, a tired coil could be contributing to the enigma . . . . . .