Thermostat changing

[sil53]

Ok, so I've done the searching, and the reading, and know what I'm doing. Done it often enough on the last couple of cars anyway.

Basically, Engine temp sits at just above the first white line, and gets to centre if left sitting stationary with the engine running. So I'm pretty certain the thermostat has failed.
Got myself a new one, and the coolant.

I went to make a start on it the other day, but it was so cold outside my fingers went a bit numb, and I didn't fancy fiddling around if I can't feel what I'm doing.

As my Z3 was going in for a clutch replacement the following day, I decided to ask them if they would be able to do it, once they had replaced the clutch. With the answer being that they'd take a look, but wouldn't promise to do it.

When I got it back, they said they hadn't fitted the thermostat, but did say why.
Apparently, it is common for the bolts holding the thermostat housing to the block have a tendency to sheer, which obviously makes life much harder. As they would need to remove the sheered bolts, and then replace them aswell.

As such, I have been quoted 2 hours labour, if it all goes smoothly, or up to 4 hours labour if there are issues, like the bolts sheering.

However, reading the threads on replacing them, I haven't yet heard any horror stories about this actually happening, so I wanted to make sure that the garage weren't just trying to fob me off as they didn't want the work, as they are rather busy. Or if the stories of this happening, don't seem to surface through my search criteria.

If its any help its a 1999 Z3 1.9

Cheers

[Brian H]

Certainly not heard of thermostat bolts shearing, quite an easy job IIRC. Usually the biggest pain to swap is the water pump as this can stick in situ and needs to be teased out.

[sil53]

Cool. It did strike me as an odd comment, as I hadn't heard of it happening before.

It definitely seemed worth double checking though, as I don't really fancy having a go, and then finding I'm the unlucky one, then having to get it recovered to a garage to have the bolts removed haha.

Cheers buddy

[Southernboy]

That has to be a crock of s"*t if ever I heard one....the bolts are steel, the heah is alluminium...if anything gives it would be the all threads in the head. You might find it adviswable to do the job after slightly warming the motor if it's seriously cold. Also, don't "jerk" the bolt loose...place the socket over the bolt head and gradually increase torque until the bolt begins to unscrew.

[Boysie]

Oh the olden days
To change the thermostat in the sprite took about 10 mins

[Del]

Definitely never heard of these bolts shearing before. They are quite lightly torqued as the thermostat body is plastic. Sounds like they weren't keen on doing the job for some reason either because you were supplying the part and eating into their profit margin or the fact that bleeding the air out afterwards can be a bit of a fiddle. It's a relatively easy job to change and one of the first I did when I got my car.

[Mike Fishwick]

Maybe they had confused the thermostat bolts with the VANOS mounting studs on some M engines. It does not give much confidence in them does it?

[Boysie]

What's Stat

[henrycrun]

FWIW when I went to change mine, (11 years old) two of the bolts were rusted in solid.
I then gave the job to my man who did snap off the heads, but then performed some magic to rescue the situation.

[sil53]

FWIW when I went to change mine, (11 years old) two of the bolts were rusted in solid.
I then gave the job to my man who did snap off the heads, but then performed some magic to rescue the situation.

Oh, ok.
Just incase then, do you know what magic he worked? Always worth having a backup plan for these sort of situations. Especially considering the amount of...crap...that has coated the lower two thermostat housing bolts.

Would it be worth trying to get some penetrating fluid through before making an attempt, something like wd-40 or GT85 to try and lube the bolts up a bit to reduce the risk of this possibly happening?

[Fender2004]

Did mine a few weeks ago with no problems

[Mike Fishwick]

My usual way to remove sheared or un-removable bolts (eg: those with the corners rusted away) is to drill a clearance hole down the centre of the head, so that it falls off, leaving the shank. The thermostat cover etc can then be easily removed, and the bolt shank unscrewed with a stilson wrench - better than a Mole wrench for gripping circular-section things. Some heat and penetrating oil may also help too - I use a 1:1 mixture of engine oil and diesel.

If the bolt has sheared flush with the surface it screws into, then drilling out is the only way, but this takes a bit of skill and starting with a small pilot drill. I find that the Black & Decker 'Bullet Point' drill bits are the best around, as they do not wander, and are made of decently-hardened steel.

Socket headed bolts with a worn hex end are usually easy - just drive a suitable Tork key (of the type which fits a socket set) into the worn hexagon, and apply plenty of torque wile striking the end of the socket expension with a large hammer. As above, heat and penetrating oil help too.

Remember to coat the new bolt swith Copa-Slip, and reduce the torque used to screw it up - use some judgement.

[Robert T]

For those of you wondering what the heck a Stillson Wrench is - see http://en.wikipedia.org/wiki/Pipe_wrench

Cheers R.

[Boysie]

Somewhat old fashion
But a very handy tool I use at work in various sizes

[Del]

This thread is becoming enough to scare anyone from ever touching their thermostat again.

The bolts are only torqued to around 6.5 ft/lbs (equivalent to around 78 in/lbs) sounds like some previous owners (or BMW workers) may have torqued them to 78 ft/lbs

[Mowerman]

In this situation the bolts are not "rusted" in, they seize as a result of electrolytic reaction between two dissimilar metals. i.e the alloy head and the zinc plated bolt. If you are taking out the old ones then I would suggest giving the point at which the bolt meets the head a good dosing of penetrating fluid, Mike`s idea of engine oil and diesel is good or use something like Wurth Rost Off (spelling is correct) at least twice 2-3 days BEFORE you want to do the job. When reassembling use a LIGHT smear of copper grease around the thread to prevent the bolt seizing again. Cheers, Steve.