Just had the timing belt and waterpump replaced on my 86 S3.
After idling for 5-10 minutes, the timing belt warning light will appear. The belt is tight.
Turn the engine off, start and the timing belt light does not appear, until 5-10 minutes later.
Any suggestions. Sensor?
If you or someone else just did the t-belt, there is a good chance you
have an electrical problem. It's very possible that the wire that
connects the tensioner to the t-belt cover (inside the cover) was not
reinstalled, the wire that plugs into the t-belt cover on the outside
was not reinstalled, or messing around with that old wiring shorted
something out. I recently had to replace a section of my external
t-belt cover wire which had frayed. Prior to the fix, I had the same
symptoms you have. The several minute delay in the warning is the way the system was designed to work.
So, I suggest you start looking at the wiring first.
As Randy points out the timing belt tension warning system has a built in
time delay 3-5 minutes during which the central warning brain is not looking
for a ground . After the delay , the metal contact on the tensioner arm
which is insulated from the water pump by the plastic bushings on the
shoulder pivot bolt
must be touching the pin in the tensioner to be grounded . This way if the
tensioner pin is not touching the arm the belt must be loose and the warning
brain displays the dreaded belt tension light . But if the single wire which passes through the plastic cam belt cover gets stretched and broken you now have an open circuit (no ground) and you get the warning immediately after
the delay . Some mechanics have been know to just cut the wire and attach it to any bolt on the engine this gives it the ground forever! You can test the circuit by temporarily grounding that wire and running the engine until the
time delay is completed and see if you get the warning light if the light does not come on the problem is not between the new ground and the brain but between the new ground and the tensioner arm contact .