'96 850 Thermostat Housing Bolt Stripped

moesvolvo · Post by **moesvolvo** » 31 Jul 2017, 21:06

Hey guys, so I'm in a bit of a pickle...

Recently bought a Thermostat from FCP Euro because my engine temp would occasionally drop down to the 4 o'clock mark and go back up to the 3 o'clock mark, instead of constantly staying at he 3 o'clock mark it should be at.

So I looked at the tutorials and figured this would be a simple job until I was faced with 21-year-old T40 bolts. I blasted them with penetrating fluid and one came off with a bit of elbow grease, but the other one wouldn't, no matter how nice I asked it to come off. So after stripping it like the lucky idiot I am, I resorted to this video:

I've only gotten up to the chisel+hammer part, and the damn bolt still won't come off, and I don't want to hit it harder than I have because I definitely don't want to replace the housing unit. I've added pics of my current progress here (

So now I'm stuck wondering what to do next? I can't seem to find a dremel tool to rent in the Metro-Detroit area, so that I could cut a line in the head and get a flat-tip screwdriver to screw the sucker off. But if any of you are in the Metro-Detroit area and have solutions, I'll gladly buy you a pack of beer.

Post by **j-dawg** » 31 Jul 2017, 21:18

Left-handed drill bit? Common way to extract broken bolts. Looks like Robert successfully reaches the head of the bolt with a right-handed bit; the lefty should be no harder and may get the job done by itself.

Post by **cn90** » 31 Jul 2017, 21:29

Just get a long drill bit and drill the bolt's head off.

moesvolvo · Post by **moesvolvo** » 31 Jul 2017, 21:54

Seems like my drill bit was probably bald, since I did go the route of using a right-handed drill bit. I'll buy a set at Lowes later this week and retry. I thought I drilled a good bit into the head since I measured it and the drill went past the head.

Post by **erikv11** » 31 Jul 2017, 22:58

It looks like you are getting close, you just need to drill the hole successively larger until the head falls off or can be pick off.

Post by **j-dawg** » 01 Aug 2017, 06:21

Remember that you need something to grab to rotate this screw out once you've removed the head. I'd be wary of drilling too far in lest you turn all of the screw above the engine block into a thin tube that will be crushed when you try to grab it with pliers or vice grips.

Post by **ZionXIX** » 01 Aug 2017, 07:06

A larger bit is better in this case as it will allow you to to destroy the head of the bolt without drilling too deep into the bolt itself. Just go slow and keep checking it. Some kind of lubricant would not be a bad idea. Just whatever is on hand, WD40, etc...

I suppose you could also sacrifice a socket head by hammering it onto the bolt head and twist it off. It might even loosen the bolt a bit for you.

Post by **abscate** » 01 Aug 2017, 07:26

Center punch it dead center, then progressively work drill up in size in 1/16 steps

If you arent perfect dead center, don't worry. As you get close to the side of the hole, make smaller drill steps until, like magic, the drill touches the threads on the block. Sprinkle PB Blaster and let sit, and the screw will back out with a vice grip. Usually you don't even get to the last step, the tension release of the threads and vibration will loosen the screw

Post by **rguzz** » 01 Aug 2017, 09:29

I think I have an extra T Stat housing (the aluminum piece) if you need it. They are available and inexpensive, relatively, even new ones if I recall.

Post by **cn90** » 01 Aug 2017, 09:55

With one bolt out, you may be able to rotate the tstat housing back and forth to loosen the other bolt a bit.