The very rough diagram below outlines how I adapted the kit for the W126.   Note the diagram is not to scale and in reality the vacuum lines do not have 90 degree bends.

There are a number of differences between the W126 and W123.  The two biggest are probably the inner firewall and multiple outputs for the heater core.   I have covered the coolants lines previously.   I also wanted to mount the vacuum solenoid inside the inner firewall.   In the end I installed it where the monovalve used to reside.   The movovalve elimination kit suggests putting a t-piece into the vacuum line for the climate control system.   The W126 is a big different in that it has one way valves in the firewall for the passenger compartment vacuum consumers.    Each vacuum valve provides 2-3 outputs for vacuum consumers.   Instead of cutting one of my lines, I just replaced a valve with two outputs with a new valve that has three outputs.     That way any vacuum leak should not affect other systems.

The photo below shows the new valve and the line I installed to the vacuum solenoid.   It is the new looking valve at the top.   The black vacuum hose connects to the solenoid located that the top centre of the photo.

Next step was to install the vacuum orifice line.   This line is essential according to the supplied instructions.    This is the clear line that can be seen in the bottom of the picture above.   One end of this line has a tiny hole that lets a small amount of vacuum bleed out.   This is poked through one of the firewall grommets.   It then links into a T-piece between the solenoid and the vacuum valve.    The diagram above shows how I have set it up.    It is shown in blue although the line is actually clear.

I decided to take the car for a test drive.    This had a surprising conclusion.   I assumed that when the vacuum lines were connected to the vacuum solenoid without power, the valve would be closed.   This is not the case.   The valve is actually open.   Still, it did prove that the valve works!   Once I disconnected the vacuum I could see the valve close.

The final step was to install the electrical connection.   The vacuum solenoid uses a more standard connection than the micro connection used by the monovalve.   The movovalve elimination kit provides the proper Mercedes electrical connections.   These require soldering.   The combination of the available space, only having two arms and my lack of soldering skill made this quite difficult.    I cheated and soldered the connections onto two short lengths of wire on the workbench and then crimped it to the wiring harness.

Back out for another test drive the car behaved exactly as it should.   Driving around normally with the climate control set around 20C, I had no intermittent heat.    Moving the temperature wheel to hot, and plenty of heat was available.    I omitted the auxilliary water pump so I have probably compromised my heat when the car is idling for prolonged periods of time.   However, I’ve never had any problem with any of the older models that do not have this feature in the warm Australian climate.

This installation has been more involved than I anticipated, but it would be much faster to do it again on another W126 V8.   I could have done it much faster by just mounting the valve on the outside of the firewall, but I wanted to make it a neater job since I plan to keep the car.   I also took the time to swap the radiator, coolant hoses, expansion tank, low pressure hoses, clean the cowl drains and install new seals and more.

Time will tell, but the Movovalve elimination kit seems like a good option for the W126.   Especially when the only monovalve available is the MTC unit.   I would also note that this installation was done in the way I decided to do it, and there are other simpler ways of doing  it.

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Looking further my design wasn’t going to quite line up.   Once I put the elbow piece on the end, it was too long and the hoses were bent too much.     I didn’t have the clearance to have another join between the heater valve and the engine block.

My solution was to use some hose offcuts to try and find a single hose that would join from the engine to the heater valve and replace the factory hose.    I created this, tested it and based on it working, I went to Supercheap Auto to find a hose that matched as closely as I could.

In the end a hose from a Toyota Hilux LN106R 2.8 I4 Diesel fit well.    I just had to trim off the ends to use the bend that I needed.  The fit is not perfect, but it is close enough that it is not putting too much pressure on the hose.

I didn’t want to use the joined up bends because the place where the join needed to go was where the hose went through the firewall.   The clamps may have chafed against the firewall.    The single piece should work much better.   Once I get a few more parts I will be able to re-install the radiator.   From there I can make sure I don’t have any coolant leaks.

From there, I was able to install the heater valve  and join it to the engine block.    Next step will be install the solenoid and vacuum connections.      The hoses will be eventually hidden by one of the control boxes.  I think it is for either the ABS or the CIS-E system.

The post W126 Monovalve eliminator – part 3 appeared first on Classic Jalopy.

In the first part I removed the W126 monovalve, auxiliary water pump and other hoses.   This gave me the room to give the area underneath the heater hoses a good clean.   There were some leaves and other detritus.   Its important to remove this stuff it can cause rust.  The mud stays wet far longer than if the area was clean.

The picture above shows the cleaned area.   It also shows the space I am going to fit the new components.   The two outputs from the heater core are seen on the right, and the hose back to the engine in the middle.    The bracket where the W126 monovalve used to go is on the left.

My plan is to use a T-piece to join the two outputs, run the coolant through the heater valve, and then place the vacuum solenoid where the W126 Monovalve used to go.

The picture above shows the setup I plan.   I have a few more hose clamps on order before I can fit this.   The clamps that went on the W126 monovalve side were too large.

A vacuum line will go from the end of the valve back to the solenoid and the whole thing will be covered up my the control box that was there before.   I used new heater hose except for the bend, which was in good shape.

Once the new hose clamps arrive, I will finalize this assembly and then move on to changing the radiator.   The new assembly is slightly too long but the flexibility of the hoses should hopefully allow it to work.

The post W126 Monovalve eliminator – part 2 appeared first on Classic Jalopy.

It used to be possible to purchase a monovalve repair kit from Mercedes or Bosch.  The supply of these has now dried up.   There is a kit from a company called MTC but all the Mercedes Forums and facebook groups are litted with stories about how this part never works properly.   A friend of mine put me onto a company called Klima Design Works that offer cooling system upgrades for W123 and W126 cars.    They have a monovalve elimination kit for sale.   Their kit is focused more at the W123, but can be adapted to the W126 as well.

The kit uses a vacuum solenoid to turn off the coolant flow instead of the electromagnetic monovalve.   I especially like that the valve is closed if something goes wrong.  Here in Australia it gets very hot, and A/C is used far more than heat.

The W126 system is a bit more complex than on a W123.   For starters, the heating components are behind the first firewall and the heater core has two outputs that go into the monovalve instead of one.   Klima Design Works suggest leaving the W123 monovalve in place and putting their heater valve upstream of the monovalve.    They do suggest removing some of the components to increase flow.

The picture above shows the coolant flow for the heater.  Its not 100% correct as this picture shows the duo valve for the manual climate control, but other than that, its the same.  The coolant enters the heater core via hose 68, and exits through hoses 50 and 53 where it enters the monovalve.   The monovalve controls the flow of coolant.   There is an auxiliary water pump (26) that helps flow coolant at idle to generate more heat.

The hoses are exposed when one of the control boxes (that sits in the metal frame) is removed.   The monovalve is on the left, hoses in the centre and the auxiliary water pump underneath.

The simplest way to install the kit would be to cut the hose on the engine side of the auxiliary firewall (hose 68) and install the heater valve there.   That seems like a bit of a hack job to me.   I want to keep the components on the other side of the firewall as the factory did.

The advantage of leaving the monovalve in place is that the car will look more original.   Having said that, removing it can easily be reversed, and I am planning to remove it and the auxiliary water pump.   The auxiliary water pump is only necessary in very cold climates, and it is one more thing to leak and cause problems.   On the Series 1 cars it can cause major problems as it is unfused.   Best case it takes out the climate control unit.  Worst case it causes a small fire.   The Series 2 cars don’t suffer from that problem and disable it if too much current is drawn.

I am thinking of combining hoses 50 and 53 with a T-piece.    I would then mount the heater valve on this combined hose and join it to hose 59.   This would be the simplest solution.   The heater valve would sit where the auxiliary water pump used to be and the solenoid would sit where the monovalve used to be.   Other than cutting hoses (which are consumables) I won’t be permanently modifying the car in any way.

The picture above shows the removed monovalve, auxiliary water pump and various bracketry.  It is a very fiddly job removing all this stuff is there is very little room to work between the two firewalls.   Still, with these components removed there is now plenty of room for the new heater valve and solenoid.    The picture below shows an elbow piece as an example of how the hoses will flow.

Removing all these hoses is a good opportunity to clean out the leaves that have accumulated underneath the hoses.   I’ve also removed the cowl coverings to give things a good clean in there.   It was necessary to remove the control box bracketry.

The post W126 Monovalve eliminator – part 1 appeared first on Classic Jalopy.