Hi guys, thanks for the complements!

Warren - the part number you'd order from the dealer is different than what's cast into the head. Look on the head, above the #2 and #3 injectors. You will see a number that is something like 603-016-xx-01. Only the 7th and 8th digits are important. If "xx" is number 15 or lower, it is the old head that is prone to cracking. If the number is 17 or higher, it is the updated head which is pretty close to crack-proof, at least I haven't heard of one failing (yet). Number 17 is what should be on all 3.5L engines. The latest version, what you would get new for ~$1800, is number 22 I think. The heads with the problem were on 1986/87 300SDL, 300D, and 300TD's (all 3.0L). Mine is the 300D. All the 350SDL's and S350's had good heads, but bad connecting rods - different story there.


Steve - I'm not 100% sure. I believe if you check out some A/C supply places, you can buy a can of spray that's designed to clean the evaporator. Normall you pull the blower motor out, or something, so you can get as close as possible to the evap to spray it in (follow directions on the can). I have never done this on my cars though (but I need to on one of them). So I don't know if this will work for you or not, but it's worth a try!



Best regards,

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

OK, GSXR, now I'm confused. I have read about the bent 350SD conn rods. I have also read that it was caused by cracks in the cyl head letting coolant into cyl 1 and causing a hydrostatic lock, ergo a bent conn rod. I have also read about the expensive re-engineering done to the engine. Is this incorrect? What is the correct story on rough running 350SD's?

Thanks a bunch

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Warren, the bent rods are correct, but the cause is not the cylinder head. The 3.5L heads are great. The cause appears to be weak connecting rods. There was no major engine re-design, just new rods, AFAIK. There was a great page on MBZ.org with this info but it's now gone, possibly lost in the server crash last fall. Here's what I dug out of my archives. Also search the ShopForum archives:

From: alt.auto.mercedes #46707
NEWSLETTER: 3.5 Liter Turbodiesel
Posting-Date: 6 Jul 1999 19:33:14 GMT

INTRODUCTION

This newsletter is being made available via the world wide web to all those
interested in the problems with the 3.5 liter turbodiesel engine used in
S-Class Mercedes between 1990 and 1995. It incorporates significant new
research and information and the input of several list members since my last
communication some time ago.

Briefly, this engine has problems. With distressing frequency these engines
show significant, grossly premature wear, requiring expensive rebuilding.
Symptoms are excessive oil consumption, mechanical noise, smoke, and a
throbbing idle. Diagnostic procedures usually reveal that one or more
cylinders have compression that is below specification, with excessive
variation in the compression among all cylinders. Mechanical teardown
frequently reveals cylinders that are out of round and connecting rods that
are bent. Catastrophic engine failure has occurred quite often. These
problems are clearly due to a design defect that Mercedes refuses to
acknowledge. These problems can not be prevented with any sort of routine
maintenance, nor can they be forestalled with changes in driving behavior.
In essence, the engine self-destructs during normal operation. Symptoms have
appeared as early as 50,000 miles. Due to the expense of individual
repairs, Mercedes honors warranty repairs only after considerable pressure
is applied. Out-of-warranty claims are summarily rejected.

The newsletter can be downloaded at: http://home.att.net/~thcg/mbnl.pdf
(this link is dead now. Anybody have a new one ?)


(this is an Adobe Acrobat file and you will need Acrobat to read the
newsletter)

Copyright 1999 John A. Blazer. May be liberally quoted or copied, provided
attribution is given.


This is the first substantive bulletin to those interested in this engine.
Hopefully the mailing list is relatively clean. If you know of someone that
should be added, please advise.

Why this Group? Because this engine contains a design defect. It
demonstrates significant wear quite early. It is expensive to repair.
Mercedes will disclaim responsibility whenever possible.

Which Cars? S-Class TurboDiesel Mercedes model years 1990 through 1995.
Includes W-126 with engine 603.970 (1990 350SDL, 1991 350SD, 1991 350SDL)
and W-140 with engine 603.971 (1992 300SD, 1993 300SD, 1994 S350, 1995
S350.)

Symptoms? The most common symptom is excessive oil consumption - 1 quart in
as few as 100 miles is not unheard of. Other symptoms include throbbing
idle, smoke, mechanical noise. Many owners report an episode of the engine
'bogging down,' 'grunting,' or similar such description, followed by a puff
of smoke.

Diagnostic Steps? Monitor oil consumption very carefully. Opinions vary on
what is 'normal,' but certainly an increase in consumption needs to be
investigated. Most people consider 1 quart per 1,000 miles to be acceptable;
1 quart per 500 miles is probably not.

Next step is a compression test. A wet and dry leakage test will help
determine whether problems are related to rings, or to valves. Engine warm,
all injectors removed. Design specifications call for compression of x-x
psi, with a range between highest and lowest of no more than x.x psi.
(Source: )

Assuming further investigation is indicated, the head will be removed. May
reveal carbon buildup in combustion chamber; worn valve guides or seals;
scored cylinder walls. Most critical: deck height, i.e., whether all pistons
rise to the same level. Differences indicate bent connecting rods and/or
pistons. Further disassembly may reveal worn or broken rings, deformed
pistons and/or out-of-round cylinders.

------------------------------

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Dave, super write up and pictures on your site for those with ACC problems on the w124's. Sounds like there most likely will be problems developing with some of these pods on the majority of cars with more than 100+k miles.

I'm wondering if access to the 7-port manifold for testing of good holding vacuum for each pod is dependent on the car NOT having a passenger side airbag? In other words, you seem to indicate that the 7-port manifold is somewhere behind/below the glove box area. So does having the passenger air bag make any difference in being able to do your recommended test ?

__________________
JD

Hi JD,

Oooo! Good point. I believe the 7-port manifold is located in the same spot, but the airbag resides in the usual glove box area. I'm not sure if you'd need to pull the passenger airbag to test the lines, or if you could pull the lower (interior colored) trim panel & still access them. If someone does this, let us know for future reference...


Thanks!

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

This thread on 124 series ACC repairs is very useful.

With some great advice from George Murphy of Performance Analysis, I've gotten far enough into diagnosing my own ACC system on a 124 series 1988 300TE to determine that the defroster actuator #38, the center nozzle flap # 40 and the two for fresh/recirculated air #42 are all leaking.

I have a couple of questions on this topic.

Anybody have any experience with ACC Actuator repair kits from Autolux? www.autoluxmbz.com

I'm concerned that their kits may result in the same limited motion Dave describes as a drawback to the actuator rebuild diaghragm kits sold by Performance Analysis.

Here's where I need some strategic advice from you folks who have been down this road. This car has 193Kmi and needs plenty of other work, my budget is tight and my time limited. I'm looking to get two more years out of it for daughter #2 to drive to college.

If I replace only the easy one - the defroster actuator #38 can be reached through the glove box opening, will I get any improvement in operation?

How do the various circuits default with no vacuum?

I never bother with the recirculator switch, so that's not really essential unless as I suspect, the ACC unit uses it to optimize speedy cool down or warm up depending on outside temp. Similarly, we can probably live with cold air coming out the side vents only and skip replacing the center vent actuator #40.

If I go this route, should I cap the now abandoned circuits at the vacuum block?

Thanks for any and all advice.

Jerry Murphy

'88 300TE
'97 E420
'97 Audi A6Q wagon
'67 Morgan +4
'37 Cadillac 7553 V8 Fleetwood Town Car

Hi Jerry,

The Autolux kits are the same as PA's - don't use them. Buy new pods from your favorite e-tailer (FastLane, Rusty, EPS Parts, etc). The system defaults to full defrost with zero vacuum signal. Replacing the defrost pod will allow the defrost vents to fully close and prevent cool air from going to the windshield in the summer. I'd definitely replace that one if it's bad. And you can live with the recirc pods, as mentioned. A band-aid fix for the center vents is to swap signal lines on the diverter and center vent pods. A signal from the center vent port, when directed to the diverter pod, will allow cool air out the center vents. It's not the "proper" airflow pattern inside the box but hey, it will limp the system along until you can yank the dash and fix them all correctly. And no, you don't need to cap off bad circuits, I think the manifold has built in restrictors that prevent any leaks from causing other pods to not work.



HTH,

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

I have a 92 300E. Where the glove box should be there is an airbag instead. Is there I glove box I don't know about?

While I'm getting this job done, and the whole dash apart, is there anything else that I should have changed while I'm at it ? it's for my 87 260E.
I've heard of the A/C related item, evaporator I guess that sits behind the dash. I'm not sure if it was the evaporator, but something A/C related... what else should be changed while the dash is open ?
thanks guys.

__________________
Whether you think you can or cannot, Either way you're right!. by Henry Ford.

Does anyone know if the climate control vacuum manifold can go TU on the 124's? The footwell vents on my '87 300 td won't open unless I use my mityvac directly on the vacuum pod. The defrost pod works fine and is actuated by the pushbutton unit.

Is there a way to diagnose why my footwell vents don't operate correctly, and is this most likely a failed pushbutton unit? It's been rebuilt by the PO at some point.

BTW: Thanks for the great pics Dave--I find your website very helpful for us 124 owners.

Thanks

So far, I haven't heard of a bad 7-port manifold. Usually it's the pushbutton unit failing to provide the proper signal. But, there's always a first time! Perhaps check in the factory CD-ROM service manual, in the ACC section, there is some good troubleshooting info in there. If all 7 of your lines hold vacuum, consider yourself lucky - for now!

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Benz300,

Ooops! I missed your post. While the dash is out, replace ALL and I mean EVERY ONE of the climate control vacuum pods with new ones from FastLane or Rusty. Replacing the evaporator is an even more extensive job, and while 124 evaps are prone to failure, I would not change one out that was good and showed no evidence of possible failure. It is NOT cheap and NOT fun to do. And, you'd need complete A/C tools to evacuate the system, pull vacuum afterwards, and recharge. It's worse if you have a R-134a system, as you need to work fast and get the system sealed & under vacuum ASAP, since the PAG/POE oils soak moisture out of the atmosphere rapidly when the system is open. This isn't a big deal for R-12 systems with mineral oil, but those are becoming more rare (sadly). Bottom line, do all the vac pods, and replace any brittle vac tubing & rubber fittings (they're usually OK though).

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

gsxr:

Was your center pod hooked up and working right? I've just extracted mine out of the heater box, and was a little surprised to find it ... not hooked up at all. There's a short length of hose running off the center hookup on the switchover valve, but it's capped off. Wondering if it came from the factory like this ('87) or if it was a quickie fix for something else somewhere down the line.

No, that's not normal, it should all be connected. Sounds to me like it was leaking and someone capped it off to prevent the leak from affecting other pods. Test everything with a MityVac, replace the leaking pods, and connect up all the hoses...

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Hi Dave.

Thanks for your posting on the vacuum pod replacement, and especially the clues about Y7 being in the glove box. The pictures from the CD are so poor that it is not possible to see that they are inside the dash.

After spending a day and a half digging around my ACC to see what the problem was, I've decided that most if not all of the pods are indeed bad. I'll be ordering some sooon.

I wonder if you have references to the 124 manual procedures for removing the dash. I'm not looking forward to it as I don't have much experience with this level of repair. I figure if I can review the factory procedure I might be better off.

Sean