after-run coolant pump question

[Dave.Eaton]

jouko,

confirm that the pump works, and the wiring is correct by removing the 2
wires from the thermoswitch and joining them together.  if the pump then
operates, your wiring is correct, and so is the fuse - culprit therefore is
the thermoswitch.  if not, check the fuse (not sure on the mb which one this
is).  afaik, the fuse on the 10v motors also powers the injector cooling
fan, this may have been removes with the injector-fan-adectomy.  only if
these do not check out is the culprit likely the relay.

also, check out http://www.teleport.com/~scottmo/cooling.html

hth,
dave.
-----Original Message-----
From: "Jouko Haapanen" <joukoh at sympatico.ca>
To: "q-list" <quattro at audifans.com>
Subject: after-run coolant pump question
Date: Mon, 28 May 2001 17:18:04 -0400

I am about to be reunited with my UrQ after a 10 month separation, as
I go back to Finland for my holidays.  The after-run coolant pump is
not operating, but I just received word that the pump does respond to
12 volts as it should.

The current flow diagram (No.39 for model year 1988, parts 1-4, engine
code MB) indicates a thermoswitch F98 and a switch unit (relay) for
coolant pump J155 and coolant pump V51 as the parts for this system.
Not having the car real close to me it is a bit difficult to diagnose,
but is the relay a possible culprit?  I can't tell you if the injector
cooling fan works, as I removed that some time ago.  It appears that
the relay unit (J155) is located on the additional relay carrier under
the instrument panel in location 5 (middle row, fifth from left).  Do
these have any history of failing?  I would think that the
thermoswitch is less likely to fail.  Or not?  The factory workshop
manual GB 000.5147.00.20 from 10.87 outlines the diagnostics on page
19-17.  The diagnosis is carried out with the VAG1527 diode check
light tool.

There are two different relays specified by ETKA for this location as
"relay, for relief relay x contact, relay location 5" part numbers 191
937 503 (12V40A) as well as 357 906 381 B (12V70A).  Which one is the
right one?

The patient is a 1988 MB engined UrQ.

Any ideas?