Replacing thermostat - a saga

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Jdring
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Location: South of Oxford, UK. 87' 230GE SWB Manual, 89' 230GE SWB Auto, 2012 G350Bluetec LWB
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Well, it was supposed to be a 15minute maintenance job, replacing a thermostat on my 230ge M102 engine.

3 securing M6 bolts and a M6 banjo bolt on the top for the breather/bypass.

But nothing is easy. So here is the work in progress and lessons learned. Firstly, I underestimated that a thermostat housing gets pretty hot, being bolted to the engine block. As a result those 3 M6 bolts get pretty seized up. I could tell this at the start, but was using a new socket set and ratchet (Xmas gift to self) and would normally tap the socket to get some shock into the bolt.

Sure enough, one of the M6 bolt heads sheared off. What a pain. Normally, I have been able to cold chisel a bolt and ease it out. But no chance here and so went to ScrewFix to purchase a bolt extractor kit (and new 20mm M6 bolts). I've never used these before, so I did a bit of YouTube research. First tip was to use a larger drill bit to flatten the uneven break and mark dead centre. Then take a small steel drill bit and drill down, dead centre.

First attempt, it somehow slid off centre. So I drilled it out a bit more, and tried again. I got it centre and then the 4mm drill bit snapped, in the hole. Grrrrr.

Managed to retrieve that with tweezers and move to trying to screw in the extractor tool. Next disaster was I made the mistake of tapping the carbon steel extractor bit to shock the bolt remains... The threads on the carbon steel head deformed. Not ruined, but damaged. So I made the pilot hole bigger and stepped up to the next size of extractor bit. This managed to grip but no more.

The square head is so hard to get leverage on. An adjustable spanner just slips off and mole grips don't really do it. I even tried some heat. I've left wd40 soaking in the socket to give it a chance. Watch this space.

Worst case, I'll need a whole new thermostat housing body!

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Nick123
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Re: Replacing thermostat - a saga
Am I pressing the wrong buttons, John? I've already tried to reply... twice! Our OM606 got a new 'stat in '21. We were lucky: no problems. Good luck with it all.
gav.helme
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Re: Replacing thermostat - a saga

Looks like you have the other 2 bolts out so tap the housing and take it off if the 3rd bolt has no head 

Then a stud extractor should grip it easily although I've often found that even though the head has sheared off the remaining bolt section is lose!

Jdring
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Location: South of Oxford, UK. 87' 230GE SWB Manual, 89' 230GE SWB Auto, 2012 G350Bluetec LWB
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Re: Replacing thermostat - a saga

Given I had drilled down the head, I was now able to wiggle off the housing top. But there is nothing to grip, so back to applying some heat (to expand the aluminium housing) and some twist on the bolt extractor screw.

I was more expecting the screw to come loose, but no, the carbon steel extractor sheared and shattered. Fed up, I decided to go all in and just drill out the seized bolt shaft. I removed the thermostat housing completely (2 13mm bolts and undo the short rubber hose to the pump). You lose some coolant at this point - about a pint.

A selection of drill bits later - barely scratched the bolt. Wth. It seems to have turned to diamond. Nothing is simple.

40 quid later and I have a new set of steel drill bits to ruin. Watch this space.... I can see a new housing being the last resort

JASONGDS
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Re: Replacing thermostat - a saga

If you have removed the housing,  can't you take it to a decent engineering shop, with proper drill, easy job for them? Plenty of copper grease on assembly, pain these always happen on a Sunday/ Bank Holiday 

Jdring
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Location: South of Oxford, UK. 87' 230GE SWB Manual, 89' 230GE SWB Auto, 2012 G350Bluetec LWB
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Re: Replacing thermostat - a saga
Broke another drill bit this evening getting nowhere and will be taking it somewhere with a drill that won't slide about and can apply some water/oil or whatever it is. But then it will need threading. I'm thinking a new housing will be simpler, but hate to be beaten.
Ben
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Re: Replacing thermostat - a saga

I recently went through this on my OM617. Two bolts came out, but the top right one snapped.

Wiggled the front housing off, centre popped the broken bolt, and used a decent quality dormer drill bit to drill out the remains of the old bolt.

I tried to save the thread, but it was too far gone. It just seemed to crumble when I chased it with a tap, so a longer bolt with a nut on the back did the job instead.

I think the key is a decent drill bit and managing to apply enough pressure to the drill - I used a right angle drill in situ. There was enough room with the fan removed. I didn't have any cutting fluid where I have the car stored, so I just used a little WD instead.

Maybe I was well practiced by this point though, because when I was replacing the water pump at the same time, every bolt broke on that.

If you've got any remains of broken extractor or drill bit in the hole, you won't drill through that, it'll just make the likelihood of snapping another bit off higher.

Jdring
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Re: Replacing thermostat - a saga

OK, so that bolt is a hard bastard and the drill just slips off it and into the soft aluminium sides.

I am going to replace.  You can find them (second hand) in Germany and Greece, but I'm not going to trust that route, plus MB new ones are only £40 plus VAT.  Cheaper than the drill bits!  It still has to come from Germany, but at least I trust the vendor!

That's the G230 out of action for a week at least.  I think I could put it back with 2 bolts, not 3, if I really needed it short term, but hopefully not.  I would run it with a loose radiator cap to avoid pressure if I did that.

Part number for the housing and thermostat housing top is:

A1022030373 body 
A1022030374 top

Lesson learned is:  take these things extra careful from the start to save this hassle. Apply some shock and heat if possible.  Do the tighten and untighten dummy runs before you even see it moving. My experience with the bolt extractor kit is that it was never going to twist that bolt shaft out.  Possibly the only thing might have been to build a bead of weld on whatever was left of the bolt shaft and then mole grips on that.

I did almost everything right, but after the head sheared!

JASONGDS
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Re: Replacing thermostat - a saga

At least the new housing is available,  we have all been there.

Next time massive pre soaking in Plus Gas, also think heat has to be used really carefully as the steel will also expand in the alloy , not much negotiation!  You can always remove the thermostat just to move the car etc, 

Stew-Em
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Re: Replacing thermostat - a saga

Thank you for sharing - certainly made me smile as fully undertsand the "pain" - I have discovered there is no such thing as a '5 minute' job on our old G's, everything becomes a trial of patience, ingenuity, and as you note new drill bits!

Jdring
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Location: South of Oxford, UK. 87' 230GE SWB Manual, 89' 230GE SWB Auto, 2012 G350Bluetec LWB
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Re: Replacing thermostat - a saga
The finished job: New thermostat housing from MB came in under 1 week. Fitted with the original bolts but new M6 ones for the top. Tested, and it was leaking!! I had put the thermostat rubber o-ring under the thermostat, instead of on top and when you tighten down the top the O-ring squirts out and doesn't seal (see 2nd pic=wrong). Stupid error but fixed in 5 mins. Job finally done.