I had a quick look at the wiring diagram to start troubleshooting.  On the W123 diesel is a pretty simple system and easy to test.  There is the switch on the A/C receiver/drier that triggers a relay to run the fan.  Unlike the petrol cars, there is no trigger for high coolant temperature, the fan is only for the A/C.

My first step was to jump this switch.  When I did so, I heard the relay click, but the fan did not come on.  Seemed apparent that my fan had died.

While I was ordering a new W123 grille insert from Niemoller I also ordered a new fan. It would seem the Bosch fans are no longer available.  Swapping the fan over is not particularly difficult.   It is secured in three places.  On the bottom, there is a small phillips head screw that holds a piece of plastic trim in place.  This trim is a filler piece between the grille and the bumper bar.  That phillips head screw also locates a bracket at the bottom of the fan.  The fan is removed with the bracket attached, as the plasic trim can flex enough to let it past.

The top left and right of the fan are held on with 8mm bolts with little brackets to the diagonal stay tubes.   Unplugging the fan is harder than removing it.  The plug is clipped onto the body of the car in a spot that is a bit hard to get to with the car on the ground.  My hoist is currently broken, but I eventually used a pick tool from the top to remove the clip and then I unplugged the fan from the bottom.

When I removed it, it was amazing how much debris was caught underneath the fan.   I cleaned this up as best as I could.  It was a simple matter to transfer the bottom bracket from the old fan to the new fan.  I was also hoping to re-use the plastic finger guard. However the body of this new fan is quite different and is not compatible.   Given the incompatibility, I think this fan should have come with a finger guard that fits.

Re-installation was a bit fiddly, The bottom mount is easy to fit, but it took some time to get the two side mounts to line up properly.  It was also a bit of a pain to get the plug clipped back in place.   In the end I did, and the fan whirred into life when I jumped the switch on the receiver/drier.

In our hot summers, a working W123 Auxiliary fan is essential to good A/C performance.

The post Replacing the W123 Auxiliary fan appeared first on Classic Jalopy.

I’m taking my 1990 Mercedes 300TE on this drive.  Now I could have taken my wife’s modern car – a Mercedes E350 Wagon.    However, I far prefer driving the 300TE.   The E350 is not as irritating as most modern cars, but I would still rather drive the 124.   I also think any issues are more likely to be dealt with easily.   An ECU or Airmatic problem is going to end the trip.

In order to reduce the odds of any issues, I had a few jobs to do to the car.    None of them were mandatory, but I think good preventative maintenance.   I have previously covered some other work I did on the car such as refurbishing the instrument cluster, attempting to change the centre vent and changing the speakers.

This trip should take me past 380,000km for the car.

Starter motor replacement

A few months ago, I noticed that when I started the 300TE, the starter motor did not seem to full disengage, and I could hear a bad noise like it was still just touching the ring gear.  It only did this a few times, but I really didn’t want to be stuck with a bad starter by the side of the road.   A Bosch remanufactured starter wasn’t all that expensive and seemed like good insurance.    I had this done at a workshop.

Tailgate soft close mechanism

The S124 has a soft close mechanism for the tailgate.   All you need to do is gently close it, and the motor will latch the tailgate.   Recently, mine has started play up.   The motor does not engage when it should, but there is a sound coming from the back like the motor is trying to work at other times.   This was mostly when I closed it firmly to bypass the soft close, or when I turned off the ignition.

I bought a second hand soft close mechanism, and gave it to the same workshop who did the starter.   They swapped the two mechanisms over, but it was still playing up.   They also did some troubleshooting.   Using a multi-meter the microswitches seemed to register when the mechanism was in a position, but they did not trigger the motor.   When the motor was triggered, it was at extremely low voltage, and the noise was coming from something else in the mechanism.

After troubleshooting for a bit, and getting nowhere, we agreed to simply disable the mechanism for now, so it doesn’t flatten my battery while I am away.   The car still works, without the soft close feature.

Oil and Filter change

As part of my trip preparation, I did a routine oil and filter change.  My hoist is currently broken, so I pumped the oil out manually.  I used Penrite HPR15 – 15W/60 Full Synthetic.

When I do an oil change, I like to remove the fuel pump relay and use the starter until oil pressure registers on the gauge.  I don’t think its strictly necessary, but its something I like to do.

Bluetooth Module wiring

When installed the correct Becker 1402 in the car, I wired in a hidden Bluetooth FM injector.   This had mostly stopped working.  Occasionally it did work, which made me think the unit was bad.

The Bluetooth unit is under the dash wood in front of the shifter.  I removed the dash wood to get to it, assuming it would need replacement.  When I removed the radio, I immediately saw the problem.    In my install, I used a relay to trigger the blue tooth unit to turn on from the antenna trigger wire.  One of my crimp connections was loose.  When I moved the radio, it came out.  To fix the issue, all I had to do was put on a new connector.

New Battery

When I first purchased the car, my battery tester noted that the battery was a bit marginal.   From the service history, it had been installed in 2017.   It probably had another year or so in it, but in November, Supercheap had a big sale.   I got a new battery for 30% off and installed it for the trip.

Auxiliary fan cut in

I’ve never been happy with the temperature of the car in stop/go traffic with the A/C on.   It sits just above 100C.   Since I owned the car, I put in an 80C thermostat and replaced the viscous fan coupling.  Those made improvements, but I it was still hot in traffic.   Given the properties of R134A, I find that it works better if the radiator is not that hot.   I’ve planned to make a fan controller box with a variable resistor like I did for the 560SEC.   However, I’m terrible at soldering, so I have not had time.

For this trip, I just wrapped the resistor around the pins for the fan sensor, and put a new plastic housing around the pins for the wiring.   This is not perfect, but should bring the fan engagement point down to the mid 90s.

Key spare parts

One advantage of driving a very common car, like a Toyota Camry, is that there are parts available wherever you go.   This is not the case in a 30 year old Mercedes.   I packed a few parts that are probably not necessary, but may be helpful on the road.     The first is a new serpentine belt and tensioner.   As a rule, I don’t like serpentine belts.  If you lose an accessory, you can’t just remove that belt and continue.    However, that is what the M103 is equipped with.   This is not something I can do by the side of the road, but having the right belt and tensioner means I can be towed to any garage for a belt change.

I also brought a voltage regulator, and a distributor rotor and cap.   Plus a few standard Mercedes relays, fuses, some wiring, cable ties and basic tools.   I take more when I go on the road trips with my friends, but I have a whole boot available, and we are pushing the cars harder.

I managed to get all this stuff squeezed into the side storage areas in the cargo area.

The post Preparing my 300TE for a family road trip appeared first on Classic Jalopy.

The heart of the controller would be a potentiometer.    I had previously used a 1.1k ohm resistor which wasn’t quite enough.   A 0-2k potentiometer should give me all the range I needed to fine tune the cut in point.   My plan was then to build the potentiometer into a housing and leverage Mercedes-Benz connectors so it snaps right into the factory wiring harness.    That way, removing my M117 fan controller would be a simple matter of unplugging it.

The only downside of this plan for me is that it requires soldering. I hate soldering and use crimped connections where possible. The wiring above shows the rough layout of the controller. This then sites inside a metal hobby box with the plastic Mercedes connectors.

Once completed, I tried my M117 fan controller prototype in my 560SEC. I had checked the resistance with a multi-meter so I was surprised when I couldn’t get the fan to kick in even with the resistance at zero. Turns out the relay had died. Swapping the high speed relay with the low speed relay had the fan whirring into life.

Overall I am very happy with the M117 fan controller prototype. I have already identified two changes I would make to it. First one would be fitting the wiring to the housing before I soldered the Mercedes terminals so I only needed one hole at each end of the housing. Secondly would be to make the wires a bit longer to allow the box to fit into a better location. I have noticed that the knob is quite sensitive so minute adjustments are required. This isn’t really a problem as I will probably mark where the normal adjustment point I like is.

I’ll probably run the prototype for a few weeks and then build two more units as the permanent solution for both 560s.

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I’ve noticed that once the coolant temperature gets up towards 100C, it has a big impact on the A/C.    I’m assuming the condenser, already marginal, is just not able to pull enough heat out of the system in hot weather with a 100C radiator next to it.    My thinking is by modifying the auxiliary fan cut-in point, I can keep the temperatures a bit lower, and provide more air over the condenser.

My 300SE has gone beyond auxiliary fan cut-in modifications to hard wire the fan to run any time the compressor is engaged.  This does help with A/C performance, as you get constant air cover the condenser.  But it has some drawbacks I am hoping to avoid on the 560SEC.    Firstly, the auxiliary fan only runs when the A/C is on.   This isn’t the end of the world, as the A/C will generally be running on hot days.  Its not ideal though.   Secondly, as the fan is always running, it even runs at freeway speeds which is not a good idea.

Instead of hacking the system like that, with a lower cut in point, I should have the best of both worlds.  More air flow during stop and go traffic, protection even without the A/C and no unnecessary running of the fan.   My 450SLC already has this modification and it works quite well.   The 107 A/C system is even more marginal than the 126 with R134A so it needs all the help it can get.

To perform the auxiliary fan cut-in modification, a resistor is placed between the two wires that come from the temperature sensor unit on the thermostat housing.   From reading various forum posts, a 1100 ohm resistor should result in a cut in point of around 94C.   This seemed ideal, as with an 80C thermostat, it should be fully open around 92-93C.   Having the fan running before the thermostat is open is just going to have them running cross purposes.

The picture below shows the temperature sensor (the green sender unit).  The harness with the two wires is the one where the resistor must be placed.    Jaycar had the resistors I needed in stock.

Most people simply solder the resistor between the two posts and call it a day.   I tried this, but the modification didn’t work.   I’m terrible at soldering and avoid it where I can.   After that, I came up with a better solution anyway.  I could build something small and removable on the bench, so the car can go back to stock at any time.

Lukcily, I had a set of bullet connectors that fitted the factory connector.  I crimped them together and tested my work using a multi-meter.   My handiwork can be seen below.   A little messy, but no permanent modification to the car.  I may try and make a neater version and replace this one.

This was actually V2.   On V1, I used shrink wrap to make it look neater.   Even though I only used the heat gun for a couple of seconds, it warped my connectors to the point I could no longer push them onto the sender unit poles.   Back to the drawing board and using electrical tape this time.

After I installed my auxiliary fan cut-in modification, I took the car for a brisk test drive and then let it idle for a bit.   It worked, but not quite as I expected.   The cut in point seemed more like the high 90s rather than mid 90s.   I don’t know if this is just because my gauge is not particularly accurate.    I may swap the modification over to the SEC for a side-by-side test.   That will have to wait as the SEC needs new brake hoses.

The picture below shows the temperature not long after the fan kicked in.   Before that I will see how the car performs in the real world.

Obviously, the auxiliary fan needs to work properly before this modification is performed.   I have just replaced the fan on the car, and have tested it working fine.

The post M117 Auxiliary fan cut-in modification appeared first on Classic Jalopy.

The first test is to jump the wires at the coolant temperature probe.  This should trigger high speed running.   The next is the sensor on the A/C receiver/drier which should trigger low speed running.   In my case, neither of these tests triggered the fan.

The last test is to apply 12v directly to the fan.   This will eliminate the relays and temperature sensors.   In my case, the fan didn’t work here either.   Time to replace the fan.

I’ve done this job before on my 1987 560SEC and had the same symptoms.   The W126 auxiliary fan replacement procedure is identical on the saloon as compared with the coupe.   The only difference is that there is more room to work on a saloon.

Like when I did this job a year or so ago, I went with a Meyle fan.  I’m really not a fan of the Meyle brand and avoid it where I can.   The trouble is, that the Meyle fan is about USD$120, and the genuine fan is about USD$500.   By the time you add in shipping and GST, the cost of the genuine fan is over $1,000.   I wish there was a manufacturer that made a higher quality product somewhere in the middle.  As the fan is so easy to replace, the Meyle one made sense.

The picture above shows the fan removed.  The little bit of extra room makes a big difference and you can have the fan out in 10 minutes.   I found it easier to leave the brackets on the fan and remove the whole assembly, then transfer the brackets to the new fan.

With the fan removed, it is worth cleaning the condenser.  The W126 A/C is marginal on very hot days running R134A.  It needs all the help it can get.  I used compressed air to blow a lot of junk out of the fins.

The new Meyle fan came in a different box than the last one.  While it looked the same, there was an improvement.   The mounting holes for the finger guard were now in the right spot so I was able to mount it.

Jumping the temperature sensor had the new fan whirring into life.    The resistor that controls the slow speed running looked quite crusty and I tested it with a multimeter.   Looks like the wire is broken inside so I have one of those on order.   This resistor looks the same as the ballast resistors Mercedes use in the ignition system, just with a different resistance.  I have one on order and will fit it as soon as it arrives.   I got a genuine one and now they are showing as no longer available so maybe I got the last one?

I’ve had to do quite a bit of work on the cooling system of my 560SEL.   When I purchased the car, the thermostat was stuck open, the fan clutch was not operating correctly and neither was the Auxiliary fan.  I feel much better about driving it on hot summer days with these systems all fixed.    I also plan to adjust the cut in point for the Auxiliary fan, which will be covered in a later article.

The post W126 auxiliary fan replacement appeared first on Classic Jalopy.

My fan would not work even when fed 12v directly.   I struggled to find a replacement fan from a brand I trust.   I wasn’t that keen on a used fan as they are all now quite old and in the hot Australian climate run quite a lot.   In the end all I could find for a reasonable price was Meyle fan.   Meyle is a brand I normally try to avoid as I have found the parts are not a great fit.

The W126 SEC auxiliary fan is not as easy to remove as on a four door car as there is less room to maneuver the fan.   The fan itself is held on by three 8mm bolts.   Two of them can be seen in the picture below.    They are at 2, 6 and 10 o’clock on the fan.   The fan is not bolted on directly, in all three cases there is a mounting bracket.   For the 6 o’clock mount, it is easier to remove the mounting bracket with the fan.   This is a 10mm bolt that is obscured by the bumper.

Once the fan is loose, it is a bit of a chore to actually remove it.   I found the easiest way was to move the strut out of the way that mounts the horns and loosen the panels that go under the headlights.   The strut has two bolts holding it on and there are three to remove to loosen the panel.   It was quite dirty underneath the old fan so I gave it a quick clean out with compressed air.

Once I had removed the old fan I was able to compare it to the new Meyle fan.   The central ‘hub’ unit on the Meyle fan is a little smaller which makes removal a bit easier.   The Meyle fan also has a balancing attachment which the factory fan did not need.  Both fans do not space the blades evenly around the hub.   The factory fan also had some little felt pads to protect the condenser.

The original fan has a finger guard, which is removable and I had planned to re use it.  As usual the I had fitment issues with Meyle parts – I could only ever get two of the mounting points for the guard to line up at any given time.   When not mounted properly there is too much risk of the fan fouling on the guard so in the end I had to fit the fan without.

Installation is generally the reverse of removal.   I found it easier to start with the 2 o’clock mount loosely, then the 6 o’clock mount.   I loosely re-installed the horn strut before loosely fitting that mount before finally tightening it all up and replacing the bolts on the under light panel.    it is quite easy to push the electrical cable through to where it plugs near the receiver drier.

It’s a shame I could not fit the finger guard.   It would be hardly noticeable I have an aftermarket fan if that was the case.    The next step was to test the fan.  I went for a 20 minute drive in very heavy traffic with the A/C on full.   I brought the car back and left it to idle for a few minutes.   Sure enough, the fan kicked on and slowly lowered the temperature.   Before I replaced the fan it got so hot I would have needed to either drive or shut off the car.

I was expecting to need to do more electrical troubleshooting once the new fan was fitted.  I was pleasantly surprised to see it whir into life after the car got nice and hot.   My next step will be replace some of the climate control vacuum elements which are preventing my centre vent from working.     I’ve kept the original one to see if it can be repaired.   The auxiliary fan in my 300SE occasionally pops the fuse so it will probably need replacement at some point

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