Stripped bolt on thermostat

[JimBee]

I strongly suggest you not consider the impact driver. It takes quite a wallop to even get some torque on the bit, let alone turn the screw. If you crack the aluminum housing and you can't get the screws out of the head where the housing mounts, you will need to remove the head to do the repair.
Instead: the day before, douse it good with PB Blaster. Then get your best bit (T-45?) that has a long enough shaft to clear the side of the head and a good driver handle. A hex shaft bit will work. Just use a 5/16 socket to turn it. Then get good firm weight on the driver handle and steady turning force to crack it loose.
If you strip out the torx teeth, get out your 3/8 drill and a good sharp 5/16 or 3/8 bit and drill the top off the screw. Use some oil on it to aid cutting. It goes pretty fast and you don't risk breaking anything else. Then use the hex head screws from the hardware store to reassemble.
NOTE: The first one I drilled off like that was so frozen into the housing that I couldn't turn it with the head off and the t-stat top out of the way. But the threads at the top of the shank with the head missing were clean enough that I could get two nuts on it (with some finessing). I screwed on the nuts, then backed the lower one up got it locked tight against the upper one, with points aligned. Then I got a socket on the nuts and was able to turn the stud out. It came hard all the way, even with PB Blaster on it over night.

[xHeart]

For anyone ever trying to replace a thermostat- FOR GOD'S SAKE - go and buy the new style bolts before you even try. There is about a 65% chance that the head will strip out on the old aluminum bolts and the replacements are around $1.00 each.

The choices after they strip out are an easy out or a drill to just cut the head off. Once the thermostat cap is off the remaining portion of the bolts seem to come off with ease.

The new style coated steel bolts are much better and they will not strip out when you go to replace the thermostat again.

Are these flange style bolts, is there a Volvo part #?

[JimBee]

Just get a couple of hex head bolts. If you got one of the torx screws out, take it to the hardware store and match it with the hex bolt replacement. Use anti-seize on the threads when you put it back together.

[rspi]

Doesn't need to go on so tight. I stripped 2 of them yesterday at the salvage yard. Have never stripped one at home. LOL I'm pretty sure they are T40. Will have the same problem with the cam sensor bolt which I did strip and had to drill out.

[cn90]

...Are these flange style bolts, is there a Volvo part #?

The PN for the Bolt is Volvo PN 986228, $0.94/each:

http://eeuroparts.com/Parts/PartDetail. ... mNumber=17

[xHeart]

Looking through the past records, I found thermostat was replace in 2005. So these screws have not moved since.
I used T40 with 3/8" driver. The one closer to Steering fluid reservoir was a straight shot, and I was able to turn it. However, the other one takes 10º - 12º angle for the T40 to reach it, and that is how it stripped while trying to unscrew.

Replacing T40 with Hex type bolt would not leave room for a socket, it is a tight space. It looks, replacing it with another T40 type screw, see cn90 comment, is a best option.

I will start with PB Blaster. It looks, using force on the stripped bolt may damage things around it.

Thinking!

[cn90]

XHeart,

I am just wondering if heat helps.
Something like using a Propane Torch (the stuff Plumber uses) and heat the bolt's head for like 20-30 seconds to loosen any binding.

What do you think?

[erikv11]

Are these flange style bolts, is there a Volvo part #?

If you're like me and have a lot of engine parts around, and it is an hour's drive to the dealer, note this: cam cover bolts work perfectly in this application. And then you will have a hex head there, not a torx. I've only got about 20 extra can cover bolts ...

[xHeart]

Stating the obvious first, the thermostat housing is made up of two parts, 1) a lower container, and 2) an upper cover. Looking to not use external intervention while working with it, therefore, I ask...
Are these two treaded?
When mated, do these two form one continuous thread?
Will the housing have hot fluid at operating temperature?

[JimBee]

I discovered the same unhappy alignment and stripped the head out on my first one. Then I found a set of 3 torx bits at Harbor Freight that just have a straight hex shank, no socket. I believe they were for a GM car.

You can get a 1/4" drive 5/16 socket with a short 1/4" extension on that bit and get a straight shot at the head. Sorry for the late post on this, though I have described this in a post on this site. That worked well on a couple I've done, but even with the new bit and a straight shot, I have rounded some out. If that happens now, I just grab the drill and a sharp 5/16" or 3/8" bit, some oil and drill the head off that puppy. No screwing around for me any more. I explained earlier how I got one shank out after drilling the head off. It was really frozen in there, so the two nuts tightened together acted like a hex bolt and I was able to turn it out. Vice grip (which I tried low enough to save the upper threads) wquldn't budge it.
Good luck.