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C126 W126 Water Pump R & R and Vacuum System Restoration

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C126 W126 Water Pump R & R DIY and Vacuum System Restoration

Hello Class! Today's topic is going to be the Removal and Re-installation of the Water Pump and the rejuvenation of the Vacuum system.


This started for me as Summer approached. I saw the temp coming up more and more everyday. Then three weeks ago I went up to see my good friends Bondavi and AzimuthAviation. On the way home up the Grapevine (a 6% grade) the started to climb up in temp to over 110C. I started to freak and pulled over near the mid point to rest it and then continues up to the top where I rested it again at the truck stop there while I ate. The rest of the way home was either flat of down hill so it did not really overheat much the rest of the way. Only uphill it had problems. T-stat? Fan Clutch?

In my DIY's I try to give an explanation of the system in question as far as theory goes, and I will attempt the same here. If you want to skip ahead go to the END OF THEORY in red.

The Mercedes Cooling System is a closed loop heat exchanger type system using a Propylene Glycol based coolant. A cooling system is designed to collect, transport and dissipate heat from a device, in this case our engine. Heat is of course generated by the constant explosions within the cylinders and of course a certain amount from the friction of the engine itself.

There are inner channels that both oil (For lubrication) and coolant (For cooling) to flow within the block and heads. We all know that water boils at 212 Degrees Fahrenheit at sea level and that is far too low a temperature to be in a metal block which could be a hundred degrees more. The water would quickly boil off even in a closed system. So we at a Propylene Glycol based additive (Coolant) to raise that boiling point much higher lever to keep "Boil off" to a point that when it evaps back from steam to a liquid, there is no or very little loos. You are always going to lose some and hence why we need to top it off from time to time.

We use Distilled water to introduce no additives or sediments that are naturally occurring or introduced into it at the purification plant. Distilled water we know has nothing in it but H2O atoms and nothing else so no corrosion can occur from it.

Coolant, or "Anti-Freeze" also has one other property that is important that we match the right coolant to our MB cooling systems. This may not seem important at fist blush, but as you will see from a metallurgy standpoint, it is most important. The coolant we will use will be Zerex G05 or MB coolant itself. They are one in the same and Zerex makes the coolant for MB.

Zerex is formulated for the types of metals in our engine and radiator. And Green and Orange or Pink coolants are designed for other makes, NOT Mercedes. Zerex is a little harder to find. I had to go to a NON-chain auto parts store that knows me and they said they would stock it for me as well as the Chevron Delo 400LE Motor Oil which we will cover at a later date.

Okay, so the Engine heats up and we need to get the engine cooler so we pump the water/glycol mix though it and the water heats up of course and we pump that out to the radiator. Well not exactly all the time. That is where the Thermostat comes in. The T-stat in our cars if you use the right one is a two stage affair. Up to 80C it remains closed to keep water within the block to warm it up. Once the engine is at 80C or so, it opens partially and lets some water through to the Radiator to cool some of it. Under heavy load such as a steep grade (Remember that 6%?) or with the A/C on, the engine will heat to 90C or more, then the T-stat opens to a point where the "Bypass" is blocked off and all of the coolant flows through the radiator.

There is a fan mounted to the front of the water pump driven by belts from the crank pulley and it will engage or disengage based on engine RPM. The faster the motor spins the clutch will disengage and let the natural speed of the Engine take over from there.

There is a single Electric fan on the outside which will kick in at 92C or, if you add a 1.1K ohm resistor as Jono points out, that will lower the kick on point to 80C or so. This provides extra ait flow through the radiator no matter the speed of the vehicle or engine. Mike Ramay wisely installed dual rear Electric fans to replace the WP fan since he lives in the desert and I may go the same route.

Hot water is also delivered to three other system in the vehicle to provide heat transfer on an "On Demand" basis and those are the Cabin heater of course, but also to the Windshield/Headlight washer bottle (That's the curly metel tubes in there) and the Windshield base heater. The Windshield/Headlight washer bottle is heater (People ask all the time "Why do you have headlight washer? Do they get that dirty?" The answer Roy or another pilot can easily answer: ICE They are to De-ice the headlights in the event of a severe storm. As any vehicle moves though a cold wet mass, ice will accumulate and decrease either visibility or lift. A bad thing in either case. (VERY BAD in the latter.. LOL))

So the Windshied is heated at the base with hot water from the engine and the Cabin heater and also the Waster bottle.

So the coolant flowing through the radiator is also adept at shedding the heat as well as the Radiator itself. The little fins this out the coolant and it flows down the tubes and the air passing through brings down the temperature and it flows back into the block and heats back up. Everything should work fine in a well designed system, but if any one component is out of whack, it throws the whole system off. If you have any leaks, coolant level dips, reducing the thermal efficiency of the remaining coolant and not transferring enough heat out of the block fast enough. The engine heats and starts to boil off the remaining coolant and you get steam into the system. Nice for a ships engine, not your car.

So clearly we need good hoses, clear of scale and no cracks of course. We need an un-blocked radiator with good flow. We need a working water pump to move the maximum amount of coolant through the entire engine to the Radiator. And we need a working thermostat to control that flow optimally.

If any of these components are bad, we could blow our motor.


So the next morning I order a new Thermostat and all new hoses and they arrived from MB and I installed them. Well I think that the pressure of the new t-stat put pressure on the main bearing and made it blow because as soon as I did that, a leak was evident out of the bottom weep hole. PUMP GOING, GOING, GONE SHORTLY!

So I looked up a pump online and it was about $100.00 to $150.00 for an Aftermarket Pump. I consulted Jono (WHAT AN OUTSTANDING RESOURCE AND HELP HE HAS BEEN THANK YOU JONATHON!!!) and he was fairly clear that a factory pump was the way to go. So I called my dealer and he quoted me $460.00!!! Holy [email protected] Batman! Then he said he would give it to me for $175! WAY TO GO MB of Valencia!

So I put the pump on order, quickly!... And I surveyed the rest of the Engine parts that I would replace. I knew I was having Vacuum issues like Charlie described, so taking a cue from him, I ordered all of the vacuum check valves and while I was at it I ordered the thermovalves on top of the engine from the EGR and the TB and I also ordered all of the color coded vacuum lines to match the factory. My Parts guy said that it is very hard to order because of limited availability. But I picked up 5 meters of each color so I will have plenty for both cars.

So the Plan:

R&R the Water Pump and all key components thereof;
Replacement of the Radiator with a Behr model with Reinforced necks;
Replacement of the Overflow tank and water level sensor.
R&R all of the key vacuum components and hard lines
Clean up as much of the Engine and bay as possible;
Possible replacement the hood pad first of the week;
Installation of a Mil-Spec 1.1K ohm resistor in the Fan Thermostat wiring to lower the "On" point to 80C from 90C (per Jono's recommendation);

Simple! Okay well if anyone has the proper documents, it's me! So I proceeded to study up on the procedures.

So here are pics of the related systems:

Here is the very front and you can see the front Electric Fan, the cheater Chinese Radiator and the top of the pump and Distributor at the top of the pic.

Moving back we can see the top of the pump, DIST, and the EGR Thermovalves and vacuum lines. 20 years of cooking next to the engine have left them completely brittle. If I even stare at one it breaks, let alone breath on one.

A closeup of the pump. If you are buying an OEM pump they will want an OEM pump back (MB is kinda funny about that!) and it MUST have the MB Tri-Star above the serial number like in this:

Look above the part number there and you will see the MB logo. It must have that logo:

I also, in the constant "restoration" on my car, wanted everything I replaced to look new so the old Brown OV Tank needed to go and I ran a new rubber hose through the fender when I did the side lights two weeks ago:

Also, I have a spare set of Valve Covers that when I was having the Air Cleaner top polished out, he said he could do my VC's so they are off being done. He quoted me $100.00 but it will take two weeks to get them back so they go on later. Also doing the PS pump top too. Should look pretty nice under there after:

All of this Vacuum stuff will be replaced.

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First we need to drain the system.
On the bottom of the RAD here you see the new drain plug under the lower water pips. The larger one goes to the lower WP where the T-stat is housed, and the smaller one goes to the OV tank. That blue fitting will be accessable through a hole in the rubber mounts on the pass side. Get a big flat SD and give it a twist and have a 5 gallon tub under it. The entire cooling system is between 3.6-3.8 of properly filled so a 5 gallon flat pan is needed. COOLANT IS HIGHLY TOXIC AND ANIMALS, ESP CATS ARE DRAWN TO THE GREEN OR PINK KIND AND IT WILL KILL THEM... So please take care!

While the system is draining (safely) get some baggies and rubber bands or small wire ties, you will need them in a minute.

Next remove the upper RAD hose and after the system drains, remove the two lower hoses too.

Next, Remove the two upper clips that hold the fan shroud on:

And then remove the 4 - 10MM bolts that hold on the front of the fan itself.

Here you can see all but the last one removed.

Next, remove the fan shroud and fan and set aside. Remove the two clips that hold the RAD as pictured HERE:

Now the Rad should be loose but not free. Safely dispose of the coolant and replace the pan under the tranny cooling hoses and disconn them and let them drain then bag them with a baggie and band.

Shown Here:

And Here:

You can now remove the Radiator and it should now look like this:

The hole on the left is the drain plug hole as you can see it better now.

Next stop is the distributor. Remove the wires and cap and disk and rotor and store or replace.Before you take a picture like this:

That will show you the position of the distributor housing relative to the engine for timing later.
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It is strongly advised that you use a 27MM 1/2" drive socket on a breaker bar and rotate the engine so that the Harmonic Balancer (HB) lines up with the timing mark on the WP so that the motor is at TDC (Top Dead Center). Do your best to keep the motor there.

Once the motor is at TDC, the Rotor wiill be at approx 100 o'clock position. NOT as it appears in my pics. I did not take a pic of that, sorry.

Loosen the bolt or Allen and pull up on the distributor and the rotor will turn about 90 degrees. Take a pic of it in that position if you can too.

Here is the pic of it JUST coming out of the socket:

That is now much it twists.

I am also replacing all of the belts with new Continentals so I just cut these off. I will buy a second new set as trunk spares, however these should be fine for the foreseeable future.

Here is after Dist and Belt removal:

Remove the sensor wires from the top of the pump and then the three bolts. Be CAREFUL as they can snap. If they do, you will just have to replace the bolt. I DID have one snap off so I replaced all three and the 8 on the pump iitself (though no bolts broke there thank God!).

Next you need to remove the fan pulley's and the HB. Inside the front of the main fan pulley mounted to the crank are 6 13MM bolts pictured HERE:


Careful not to break those either or you will have a very bad day though not as bad as if you snap one of the WP ones off. Once those are off you can slide the main pulley off and also the WP Pulley which I hope you did not force off before now!

Here you can see the HB and the timing marks. BEFORE you remove the HB make sure you use a pencil or Sharpie and mark the position of the HB and the hub. I used my impact driver as per Jono to jar the HB loose which worked perfectly. Just do not let it "Stray" too much from TDC. ALSO IMPORTANT... If you closely examine the bolt pattern you will see it is a 6 bolt hex pattern. When you line up TDC that one bolt hole will also be at TDC. That is your reference point later. That and your marks.

Okay, here you can see the crank flange for the HB mount and you can see hole #1 aligned in the approx 1 o'clock position. YES Dirty engine... Simple... Simple Green!

Here is the culprit:

All of the other bolts can be removed easily without fuss, but this little bugger is hidden behind it woth no clearance. So remove all 8 bolts in a clockwise pattern and mark them accordingly, because they are in 4 different sizes:

4 ea - N304017 008053
2 ea - N304014 008002
1 ea - N000931 008401
1 ea - N000931 008189

Don't know which is which, will find out tomorrow when the new ones get here.
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A closer look above the part number, shows the MB Tri-Star, which reveals that this IS an OEM pump, maybe the original one:

Okay, so you should have all 8 bolts out and here is the rotor of my pump:

The flanges:

AND the front of the timing case cover:

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And it a little cleaned up:

And some Simple Green to the front of the engine area and everything cleans up nicely: (Note the Hydraulic pump for the SLS. With this removed, you need the Notorious "Block Off Plate" you hear so much about. That is where is goes:


You MUST take a razor blade and completely clean off the front of the Timing case cover where the new WP will mount. This is of course critical to getting a good and proper seal. Take your time here Gents, this is where it matters. I took some simple green and some brand new wire brushes and still did not get all of the scale.

Jono recommends a Citric Acid Douche, which I will administer to the block in the morning and also flush out the radiator as well. I have a nearly brand new Behr Rad and will flush that out again with the CA. I have a new mount kit and I also replaced the drain plugs and seals with new.

This is where it matters so do a good and thorough job here. Take your time. I split it up into two days.

This much took me about four hours. I did need (Of course) to go to Sears once to get a 17MM wrench what I seemed to be missing. But not much more than that.

I plan on cleaning the entire engine bay if I can. Certainly the pass side when I replace the new OV tank.

Well that is the end of Part 1 (Theory and removal). Next will be re-installation and fluids.

Tomorrow I will be getting in most of the parts from MB and I will also be doing the clean up. So look for more Saturday!
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Priceless, Mike...priceless. A lot of people are going to be coming back to reference this stuff. Keep it up! :D
Love it - thanks man!:thumbsup:
Excellent!! Thanks for taking the time to do this for all of us on here.

is caring :D
Seriously - nice contribution!
I am Remiss - I forgot to, in Part One, give a BIG THANKS to Bondavi for talking me down off the ledge about the whole Distributor removal/TDC issue. He had the flu for days I kept asking him a million questions about this job. He kept reassuring me the distributor would not be an issue.

Jono also spent a very good deal of time guiding me as well so I share equally the credit of this post with them. For without their unselfish generosity of their time and most of all, knowledge. I am just passing to you all here, what these two Gentleman have bestowed upon me.

Gentlemen, I thank you BOTH, and raise my glass to you!

I also need to give a MONSTER Shout out to Eric Larzelere Parts Manager of Mercedes Benz of Valencia for Near aftermarket pricing on almost everything. Add to that that he delivered to my door like a wholesale account. And to be clear here MBV is like 60 miles from my house! I know they have "Real" accounts up here, but it is nice to be included in the "real" clients. How is that for MB Service!

A Tip of the Hat to Lenny Sage and his great Staff and Mercedes Benz of Valencia. Keep it up!
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Good stuff! I was wondering what the heck that pump thing was in front of the dist. when you pointed out that it is the hydraulic pump for the SLS.

The dual stage t-stat is cool. I didn't know they did that.

I agree that while there are plenty of talented, knowledgeable, and resourceful people here who are quick to help, there are a few ridiculously knowledgable people who deserve our support whenever possible. Such knowledge rarely comes for free as it does here.

Also, I want to point out that if you had a 500 you would be done by now (I had to add that to make me feel better about the 500's power deficit to the 560)! :p
Tip'o'dahat, Mike.

Excellent documentation. Explained the distributor removal completely.

Well thanks for that Alan, but let's not get too excited until we get it back in and it starts.

But I REALLY appreciate the vote of confidence. If I sounded confident, it because Bondavi and Jono kept saying "You can do it little buck-er-roo.." lol...

All I can say is take LOTS of pictures from all angles with a good Macro camera.

I once too apart a Turbo 400 Tranny and I had my Ex-wife video tape me take it all apart. Then when I went to put it back together, I just played it in revers slowly and studied each part, then went and did it.

I have always had the gift of being able to take something apart and instantly know how it works and goes back together. Now all I need is a exploded view diagram and I got it.

But still, there is always that nervousness and doubt. "Will it work when I Put it back together?"
Especial thank for mclare and for others as well.

What a nice,excellent, helpfull documentation that explains first the removal of the power distributor and second the removal of the water pump completely with these nice pictures.:thumbsup:
I appreciate your generous help and really if I look for such information in any web site, I will not get it. Of course, this is an indication of these guys here, what they are doing and thier participations and thier willing to help.

Again, I do thank all of you and wish you goodluck.
Thank You Abdullah2009.



I got it Sam and THANKS! Will post a thread when I get home from the Club.
you have out done yourself, hey is that jerk neighbour still giving you a hard time? I was just thinking you should install an electric fan, I did on my 420 SEL and it freed up HP and less noise. Made me nervous at first but it works fine.


I got it Sam and THANKS! Will post a thread when I get home from the Club.
No Prob! You've been a great help to me, and generous to boot!

If you've never actually read the Bond books before, you're in for a treat. They're intelligently written, though they can be burned through quickly. Less gadgets than in the movies (I love the gadgets, though), and less of the Walther PPK as well. I think Bond only used the PPK in one of the books. He also has a thing for Bentleys that the movies gloss over.

I would've responded to your gratitude in the other more recent thread, but was not allowed to. I won't complain, however. I'm glad that everyone else here was spared my terribly off-topic "you're welcome." :rolleyes:

My 3.5yr-old son likes going places with me in my car (he often chooses to stay at home if I need the space of my wife's wagon). The cooling system in my car functions flawlessly, thanks to the large wads of cash the PO tossed at his mechanic. There, now I'm on topic (though another 'thanks' was snuck in - oh dear! :eek:)! :D
Nice write up mike..:) FYI, your rotor is 180 degrees out:) No Big deal as long as you put it back in the same position.

Yes, Jono,

I remember that we talked about the 0/180 phase point and I will address this in detail when I finish this article up.

What Jono is pointing out here is that I may have the engine 180 degrees out of "Phase" with the compression (ignition) stroke. Even though the #1 piston is at TDC (Top Dead Center) it may be at the top of the Exhaust stroke and not and the top of the compression stroke. When I go to start the car, if it does not start, then I will loosen the Distributor and rotate it 180 degrees and then it will be back in phase or sync.

If you are EXTREAMLY CAREFUL when disassembling, to always keep the engine at TDC and remove the Distributor at TDC, and then Replace it back at TDC, you will not need to Re-Sync it. I did not do this.

THANKS Again for all of the help.

Part II - The Reassembly

Hello Class -

Today we will be re-assembling the water pump, distributor, radiator, and cleaning up some more vacuum lines.

To start off with here are all of the parts that came in late Friday from MB and from my local parts store:

As you can see quite a haul. First off the Fluids we will be using:

Zerex G06 Anti-Freeze ONLY. You can see here on the label "Approved for Mercedes". Redline "Water Wetter" You can read about it HERE and I am going to do a twin flush. I have Mercedes Citric Acid flush and I am also going to use McKays Triple action.

Here is the vac line (Red and Yellow)

Black and Blue:

The replacement Sensors. The Blue two pole is for the fans and the single pole goes to the temp gauge on the dash:

Gasket sealer and a wire brush to power off the scale out of the intake and outlet pipes. (White Litium grease I always have on hand.

Here are the Vacuum check valves that control the interior devices such as the A/C flaps and the door lock system. These are the ones on the secondary firewall: (Note that I even replaced the "Spider" the crossed vac fitting.)

The replacement bolts, new bushings for the Air Cleaner:

New upper hose:

The new factory pump and gaskets:

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