Coolant leak, 1979 300TD (W123)

So I just discovered this coolant leak today, and the source was obvious. Pictures, if they help, live at http://www.fancy.org/mb /. The coolant is leaking out of a crack in an aluminum (I think?) box that
sits just under the intake; there are four coolant lines connected to the bottom of this thing (or maybe three? memory is faulty; two in front and at least one in back) and then a bunch of wires and maybe vacuum hoses out the back. There's enough stuff connected here that I'm guessing it's a fairly important piece of the vacuum system controls, although Chilton's is absolutely useless for this as the only vacuum info they have is for exhaust control on gas/petrol engines.
I'd like to start calling the local wreckers to see if anyone's got a W123 on their lot that I can yank one of these out of. With any luck this part was unchanged for the whole model run. :) Any advice?
thx, -tom!
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http://www.performanceproducts4benz.com/productpage.aspx?pid 9850&name=Digital+AC+Servo+Upgrade+Kit
That is the upgrade for the old, electronic attempt that MB tried in 1979. My 84 300D does not have this, but my 1980 450SL does. Ton Lambach has added this to his MB and appears to be happy with the upgrade. Get a copy of performance Products Catalog and it will give you a great parts breakdown. Not always the cheapest, but their catalog sure answers a lot of questions...And prices are included...
Bill 1984 300D 185,000 miles 1980 450SL with 215,000 miles

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Bill Pelka wrote:

So this thing that's leaking is the Climate Control system? Holy hell. That explains the amazing amount of harness it has. ;) ...and pretty much answers the previous posts, "hope you didn't get one with a bad climate control system." heh.
thanks a bunch. Now to see if I can salvage one easily or if I want to throw down $700.
-tom!
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Tom Plunket wrote:

Dooh! That's the climate control servo all right. The coolant leak is usually from cracking and is one of the major failure modes I mentioned previously. I would not recommend fooling around with salvage ones as these are the weakest link in these cars and there is no easy way to tell if one is any good. I guess if you could find one where you could try it out and only pay for it if it works and the price is reasonable, that would work. But I sure wouldn't pay $100 for a used one on Ebay that someone claims works, with no guarantee.
Performance Analysis in TN sells rebuilt ones for I think around $600. They subsitute an aluminum bottom half, which eliminates the cracking failures. Also, they have a 1yr warranty and after that will replace it indefinitely for $100. That's the one I have.
As mentioned above, the conversion kit is the other alternative.
You have a somewhat more difficult situation, in that with this car that you just bought, you don't know what else works or doesn't work in the whole heat/ac system. That's going to make repairing it more challenging than if it were just a leaking servo problem.
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snipped-for-privacy@optonline.net wrote:

Ah, I didn't realize the OEM ones were plastic. This one is all-aluminum, so for whatever reason it's cracked regardless and I'm thinking the conversion kit is the way to go once all the other issues are addressed. Winter's coming, but SoCal winters mean you wear a long sleeve shirt if you want the windows rolled down at night. ;) ...and it doesn't appear to leak coolant as long as the heat is off, so all's well. Temperature dial on 65. :)

That is true, however I do have patience and a desire to make this thing work so hopefully that'll overcome!
-tom!
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Tom Plunket wrote:

On the conversion vs a rebuilt servo, here's how I see it. The advantage to conversion is that it replaces the whole thing for good, including the amplifier that is under the dash that drives the thing. These fail too, but not all that frequently in my experience. They cost ~100 or so.
The plus for replacing the servo is if you get one from Performance Analysis, after the one year warranty, they will replace it if it fails anytime for $100. I've probably averaged 6 years per servo, and all the ones previous to the current one were plastic, not the alum shell which Perf Analysis uses. So from now on if it cost $100 and I get at least similar life out of it, that isn't bad at all. And hopefully the alum will last longer.
The obvious question is what happens if the conversion kit fails at some point? Do they replace or repair it for some reasonable fee, or do you have to buy another one?
Winter's coming, but SoCal winters mean you wear a long

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trader4 wrote:

It's got a five-year warranty, and it seems that the parts that have a high incidence of failure (i.e. the valve for the heater core) are simplified and likely much cheaper (and certainly much easier) to replace. Alas, I have not communicated with the UT folks to see if that part is available separately.
-tom!
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Here is some info to help you diagnose and fix the issue yourself.
http://www.mercedesforum.com/m_39436/tm.htm
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I'm no 123 expert but John is - here's what he says:
    The part that is leaking is an Automatic Climate Control type II Servo. It is a common albeit somewhat expensive item. There are replacement servos made out of aluminum rather than the OEM plastic, available from several suppliers one of which is www.buymbparts.com. I have one from them in my 1979 300SD and it works fine.
    The other item in question is the reservoir for the hydraulic self- leveling rear suspension. This requires a special fluid available at MB dealers and the source listed above, among others. The aftermarket fluid made by Febi is considerably less pricy than the MB fluid and will work just fine. It takes roughly 3.5 liters to completely fill the system. The tank also has a filter in it and both fluid and filter should be changed every few years (consult the owner's or maintenance manual for for the proper interval).
Johnny B.
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Johnny B. wrote, via Richard Sexton:

Ah, crap.
Ok, so the car doesn't appear to sit funny, and the ride isn't awful, but the dipstick in the tank shows nothing. I'll crawl under there tonight to see if there are shocks and springs, but otherwise if this is dry does it mean the system is ruined, or could it be really low and work not right but not be damaged? If the inflatables are still in there I'll assume it's intended to work and swing by the dealer tomorrow...
thx, -tom!
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Johnny B. wrote:

I got the MB fluid today. One liter took it up to just above the 'min' line on the dipstick. Fingers crossed that this unit is still functioning. I got another liter but will sit on it 'til I know the system works, or 'til I bite the bullet and replace the oil and filter.
How high should the back end sit if the system is operational? Presumably I could see if it's working at all if I throw a bunch of stuff in the back and then turn on the car to see if it lifts. ...and see if it spurts $25/liter oil all over the place. ;)
-tom!
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Continuing to channel the spirit of Johnny B:
    You'll have to rely on your eyes for the correct height. If the rear height of the vehicle appears to be even with or slightly higher than the front (looking from either side on level ground) your SLS is most likely functioning properly.     Some folks tried to come up with a standard for measuring F/R vehicle height, measuring from the center of the wheel to the center of the wheel arch. There did not seem to be any vehicles for which this measurement was the same, so like I said use your eyes, if it looks OK then it probably is.     It is suggested to load approximately 300 lbs or 2 people in the back of the 300TD     You can save big bucks by using the FEBI brand-name fluid. It is approved by MB for use in SLS systems.
    Hope this helps.
Johnny B.
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Richard Sexton | Mercedes stuff: http://mbz.org
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It is easy enough to test... just measure from level ground to the bottom of the door. It should be close enough to each other. Then to test the system. Have someone jump onto the rear bumper and stay there... the system should bring it back to the same height as you measured before. This is done with engine running.
The critical test is when engine is off and car rest for a couple of days. if it really sink back down, you definitely have to replace those bags by the springs. They wear out due to rubber deterioration.
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Call your Mercedes dealer to ask how much they will charge you for one of these. Mine laughed out loud as he told me the price. :>
I got a replacement from a guy in Tennessee I think it was- he rebuilds them and replaces the plastic part that breaks with aluminum. This part was also used an Chrysler products about the same time, IIRC.
Performance Analysis Company, 1345 Oak Ridge Turnpike, Oak Ridge Tennessee 37830. Phone is (865) 482-9175.
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