Thermostat Housing Bolt LOOSENING Torque - PeachParts Mercedes-Benz Forum

shertex · #1 03-31-2016, 08:21 AM

I've never replaced a thermostat before....thought I'd give it a try. This is on an OM602, on the 1989 190D I'm working on for a friend. My only hesitation is the possibility of the bolts snapping off, which I understand is fairly common. So obviously lots of penetrating oil. But, if I meet with significant resistance, what approximate torque value should I not exceed when try to loosen the bolts?

Clemson88 · #2 03-31-2016, 08:57 AM

You decide if it has to come off. I try to work stuck bolts loose by turning both CW and CCW with liberal amounts of several types of lubricants. It's tough but when I decide to take a bolt out I take it out one way or the other. It's no magic formula it just take patients, lube and sometimes a little heat.

All that helps us remember anti-seize.

vstech · #3 03-31-2016, 09:14 AM

it's not a huge deal... the problem is the bolts are THIN and often corroded...

if they break, get an easy out and remove them.

Dan Stokes · #4 03-31-2016, 09:21 AM

As usual, VSTech hits the nail on the head - they HAVE to come out. I'll agree that a mixture of penetrating oil and heat can often help but don't get the aluminum bits TOO hot. The good news is that aluminum dissipates heat like mad so it's pretty hard to REALLY screw anything up (the heat wants to leave the area you're heating and travel to the rest of the part). Doubtful that you could do any real damage with a propane torch but I use oxy-acetylene so I can really screw stuff up if I'm not careful.

Remember that if the threads pull out as sometimes happens you can Heli-Coil (or similar) the hole and fix it right up with a stronger thread than original.

Dan

Rick76 · #5 03-31-2016, 09:33 AM

If you have access to compressed air and a 3/8 impact gun, the impacts break the corrosion and remove the bolts easily. Start with the lowest setting on the gun and work up.

A 1/2 inch impact would probably be too strong even on it's lowest setting although maybe OK with reduced air pressure.

Clean the bolts and use antiseize before re-installing.

DDAY · #6 03-31-2016, 09:48 AM

Whenever there is a steel/aluminum connection, there is a possibility of the aluminum threads pulling. This can be a steel bolt into an aluminum casting or a steel tubing connector onto an aluminum oil cooler. The damage was done long ago when the installation was made and the connection was over tightened and the threads were pulled. Usually, the pulled threads can still hold the joint tight and cause no problem until the joint is disassembled. When this is the case, no amount of techniques will result in a successful disassembly.

This problem can also exist when a steel bolt is over tightened into some grades of stainless steel castings. In this case it is often called galling rather than thread pulling and it can happen at very low torgues.

Zulfiqar · #7 03-31-2016, 12:13 PM

fine tipped torch and penetrating oil or even candle wax - before you apply CCW force, try a smidge CW, this breaks the bonding and allows easier removal.

once you get some bolts a bit loose, apply heat and penetrating lube, the lube should be wicked into the bolt threads - they should come out eventually.

Demothen · #8 03-31-2016, 12:24 PM

So far I'm yet to break/round a single bolt on my w123 or my previous (mini)-restoration 74 VW using this technique:
0) Optional: wire brush the threaded side of the bolt, if possible.
1) Apply penetrating oil. Walk away for 24 hours or more. (if possible, apply to both sides of the bolt)
2) Apply oil once again.
3) Use a quality socket/wrench, apply some torque with one hand. Thump that hand with your other hand a few times - this will usually break loose any reasonably sized bolts. (Optionally, use a deadblow or rubber mallet, though obviously avoid hitting your hand. If needed, use an impact wrench on larger parts)
4) This is where I think a lot of bolts break, instead of cranking the bolt out now, apply some more oil and walk away for a few minutes. This will give the fresh oil some time to work it's way into the threads. By walking away you're also allowing the metal to cool down.
5) Slowly work the bolt in/out as necessary, try to avoid applying much torque - occasionally take breaks and add more oil. Heat seems to be the enemy here, in my opinion - it's surprising how much heat is built up just from hand cranking a bolt too aggressively.

Your milage may vary - but this has served me well. Other suggestions such as tightening the bolt a tiny bit, or applying heat, are also very good - I haven't had to use those since working on my '65 VW rust bucket back in college.

I'm a big fan of using a small amount of anti-seize when working in aluminum, or with stainless fasteners. Not sure if this is always a good practice, but for non-mobile fasteners, I generally think it's fine.

shertex · #9 03-31-2016, 01:35 PM

Thanks for all the help...will save for future reference.

Thankfully, both bolts came out easily. My biggest problem was having so little space to maneuver. Where's Marco Rubio and his small hands when you need him?