[V6-12v] Thermostat lifespan

Tom Christiansen tomchr at gmail.com
Wed Jul 5 12:41:41 EDT 2006


Quick recap: It took for ever for the engine in my 1994 90S to warm up
and I had no heat at the vents. Only in stop & go traffic would the
engine warm up (in 60-70 deg F (15-20 C) weather).

I shook the expansion tank cap and it did not rattle. This can be a
sign of a stuck valve, which, according to several list members can
cause the system to show the symptoms I describe. A new cap was about
$6.50 at the dealer so it was worth a try. Unfortunately, it did not
fix the problem.

So I replaced the thermostat, which on the AAH/AFC engines can be done
without removing the timing belt. Here's how I did it:

1) Remove belly pan, top engine cover. Drain coolant and dispose of it properly.
2) Remove radiator fans to give you more room.
3) Remove front plastic cover on engine.
4) Remove accessory belt and tensioner.
5) Remove timing belt covers. Be careful as the plastic can be rather brittle.
6) Remove the coolant hose at the thermostat housing.
7) Remove two 10 mm bolts that hold the housing. One is above the
idler/roller for the timing belt, the other is under the large pulley
at the top (use a 1/4" drive socket, universal joint, and a short
8) Wiggle the thermostat housing out from underneath the timing belt.
9) Replace thermostat and the O-ring around it.
10) Assembly is reverse of removal.

Remember to bleed the system when you fill it with coolant. Getting
the thermostat housing out is a real chore as the thermostat gets
caught on it. But it is possible to get it out (the Bentley Manual
even says so). It took me around 15 minutes to get it out. 10-15
minutes to get it back in. The whole procedure took 1.5 hours. Add 30
minutes for bleeding the system (waiting for the engine to heat up)
and tool clean-up.I took the time to make sure the timing belt was
clean and I rotated the engine a couple of revs by hand before putting
the covers on. Just as a precaution.

Relevant torques:
Thermostat housing bolts: 10 Nm
Accessory belt bolt: 55 Nm
Bleed screw in the hard coolant line by the EGR valve: 15 Nm


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