A lot of people have had problems with the T40 torx screws in the thermostat housing. Be careful...I buggered mine all up and had to get replacements from Groton. Anyway, what you want is a 6 inch long T40 torx bit...otherwise you may be able to get the screw out but there is a chance of cross threading it as you won't be able to get straight down on it with the hard fuel lines being in your way. Also, spray some loosener on those screws over night. Have read a post once by a guy who wrenched the top of one of these screws off and was left with the actual screw buried deep in the screw hole. You really don't want to do this if it's really tight. Another tip: Syphon out your expansion tank. This way you have very little spillage when you do get the thermostat housing open, and you can re-use the fluid once everything is back together. You'll have some anyway, and it will smell as it burns off, but you want to make this minimal if possible. Good luck and let us know how it goes.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.