I just went through this with another customer (list member) just yesterday.  I
actually could get the top bolt out and the housing was already split near the
bottom bolt.  I got the top bolt out and then just used brute force to push on
the thermostat housing until it broke off the rest of the way (as I said it was
split by the bottom bolt already.  Once the plastic housing broke away the
bottomm bolt was finger tight.  Very easy to remove.  You could also just get a
really nice drill bit and drill the heads off of these allen bolts.  Then the
housing should just slide off and you would have two or three inches of bolt
left to work on with vice grips.  I think I should start selling a thermostat
housing kit and includes these bolts as new.  They are only a couple of dollars
more and most of the time I wind up needing them when I replace these.  Hope
this helps.

--
Thanks,
Ken Wilford
John 3:16
http://www.vanagain.com
Phone: 856-327-4936
Fax: 856-327-2242
> Many thanks for all the assistance...and here we go with another PITA.
> Just completed a coolant flush and partial hose replacement.  The plastic
> thermostat housing is junk.  All four cover bolts are rust and the bottom
> fitting spins; the cover can not be removed.  Next the bleed valve is stuck
> shut.  So I buy a new unit from Ken W.  Low and behold the two Allan bolt
> heads do not take the 6mm wrench, even when the recess is cleaned before
> hand.
> What suggestions do you folks have?
> One idea is to remove the front exhaust pipes, disconnect the 278 hoses,
> carefully cut away the existing thermo house so vice grips can get on the
> bolt head.  A good overnight soaking in PB blaster is in order to.
> Does anyone know the dia/length of the two Allen bolts required
> A search of the archives indicates many despise this poor bit of
> engineering, although my situation is not addressed.
> Thanks for reading this and responding.
>
> Chris Hawkins
> Lost Nation, NH
> 91 Westy "Arkle"