85VW TDI Jetta, Instrument Panel Problem

[LudoVW]

The temp gauge shows normal, the blinking overheat light comes on intermittently despite normal engine temp.  Sometimes turning the engine off and on eliminates the quirk. The rpm gauge comes on intermittently.  It's not a serious problem, but I'd like to fix it, anyone with experience with anything like this? -- thanks, lud

[jtanguay]

if you haven't swapped a TDI in there, it will be an IDI

my coolant light comes on too... i think its related to the coolant level sensor... or i just don't have enough coolant?  my rpm gauge is intermittent too.  the belt is very loose and just needs to be tightened.  however your problem may be more like the alternator itself.

[LudoVW]

interesting! I didn't consider those sources as the problem, I'm gonna look into it -- thanks, ludo

[LudoVW]

blinking overheat light turned out to be a faulty contact on the coolant level sensor.  Checked the alternator and belt tension, seemed to make the RPM gauge more active, but still cuts out.  The relationship to the alternator puzzles me, is there a voltage output threshold for the instrument panel? -- thanks again for the help, ludo

[jtanguay]

when i start any vw, i need to blip the throttle to 'excite' the alternator for it to produce power.  otherwise it won't.

the tach is directly linked to the alternator speed, so if the alternator belt slips, then your reading will be either off, or non functioning.  keep trying to tighten the belt up making small adjustments until the belt seems good and firm.   too tight = bad (i had my pulley fly off one day because the p/o or whoever changed the alt had tightened it way too tight!)

[LudoVW]

I have exactly the same symptoms ... is a replacement alternator called for?  -- ludo ( interesting that the alternator supplies the RPM signal )