I created a list of items I wanted to address, with the first being the critical one.

• Occasional coolant leak after long drives
• Fix a transmission leak
• Windscreen washer not working
• Oil pressure gauge odd readings
• Slight noise from alternator
• Poor A/C performance
• Fit battery monitor

My 560SEL has 342,000km on the clock, but I use it quite a lot so it is in good mechanical shape.   Any older car can have an issue, but sorting that list out would give me confidence for the trip.  I also packed some spares with me, such as radiator hoses, fuses, the old alternator and the like.

Poor A/C Performance, Alternator & Transmission leak

I started with the A/C performance, largely because I hadn’t noticed the coolant leak at that time.   Late last year, the freon leaked out of the system, so it felt like a good opportunity to not only address that issue, but fit the same uprated condenser I have on my 560SEC.   I started this upgrade at roughly the same time as I upgraded the condenser on my 450SLC.

As with before, I got the kit from Klima Design works, and my mechanic fitted it for me.   There wasn’t any real issue fitting the kit, but the leak was found to me my compressor.   The compressor had been replaced by the previous owner about 10-12 years prior.   Based on the leaky compressor, we didn’t re-gas the system and I sourced a new compressor to be fitted on my next visit.

The transmission leak turned out to be the secondary transmission pump.   The seals were replaced, as well as the transmission cooler hoses.   At the time my mechanic noted it looked like the radiator had been leaking coolant.

I had heard some noise from the alternator, so had him replace it with a Bosch rebuilt unit.   After my experience last time, I figured the swap meant I would also have the old one as a spare before it failed.

A few months later I had the compressor changed and now had working A/C again.   It didn’t seem as cold as the 560SEC is, but it is a good improvement on what I had before.

Coolant Leak

I was only able to see the coolant leak after a long drive, and after that I would have a small puddle of coolant under the car.    The puddle was always under the middle of the car, but I could not see any evidence of leaks from the coolant hoses.

To try and narrow it down to see if it was the radiator or something else, I ran the car while up on the hoist.  I couldn’t get it to leak coolant and I checked carefully around the radiator and heater hoses.   I changed the oil pressure sender unit while the car was up in the air.

After leaving the car overnight, I had a small pool of coolant on the floor underneath where the starter was.  At least the oil pressure gauge was working correctly.

Since the leak was not conclusive, I took the car back to my mechanic so he could pressure test it.   Turns out the radiator would leak from the seams when under pressure.  I guess the coolant was running down the undershield, or being blown back onto the engine before leaking onto the ground.   A new Radiator fixed the problem.

Windscreen washer and battery monitor

Having a working windscreen washer is quite useful for country driving.  The first and most obvious test was that I had fluid in the tank, which I did.  I was also able to test the headlight washers, which did spray when the headlights were switched on.    The pumps from my parts car were really crusty.  I simply swapped the headlight and windcreen pumps over.  I now have a working windscreen washer at the expense of the headlight washer.   The headlight washer is really for snowy environments.

I also fitted a BM2 battery monitor, which I use for most of my cars.  Since Mercedes-Benz didn’t provide a voltage gauge, the battery monitor allows my phone to act as a voltage gauge.

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The A/C worked well until I took the car off the road for a couple of months to fix the fuel system.  After that, the freon had leaked out again.  A further re-gas and having the valves changed basically just gave me my road trip to Brisbane.  Clearly there was a leak somewhere.

I looked with my blacklight, and the issue was apparent.   There was green dye all over the compressor.   This isn’t all that surprising.  A/C compressors need to be run regularly to prevent leaks.  As my car was likely laid up for a while before my ownership, the seals had obviously gone.

My 240D is new enough that it uses the GM ‘pancake’ style rotary compressor, not the York.  My 240D still had the AC Delco compressor with metric fittings these cars came with.  I do not believe these are available anymore.  I bought an Omega brand compressor to replace it with.  Naturally I had the drier replaced at the same time.

I could have stopped there but decided to upgrade the condenser too.   The original condensers designed for R12 don’t work all that well with R134A.   I’ve been very happy with the Klima Design works condensers in my 560SEC and 450SLC so decided to also put one in the 240D.

I noticed in the W123 instructions it mentions that you can paint the condenser black to match the factory look. I reached out to Klima Design Works to confirm that this would not impact cooling performance.   Their reply indicated that their testing hadn’t seen any measurable impact.  I decided to paint mine before I had it fitted.

It was a pretty easy job to paint both the condenser plus the various fittings satin black.  I only painted the front of the condenser.    The back is not visible.

I had the new compressor, condenser, drier etc fitted a couple of weeks ago.   Painting it black made a huge difference in how noticeable it is.   I’ll probably go back and see how much I can paint the condensers I have in the two 126s and the 107.

Its been pretty cold in Sydney since I got the car back.   The new upgraded A/C seems very good, but I’ve not had a hot day to test it with.  I’ll be doing a trip in January for the 50 years of the W123 event, so having nice cold A/C will be a plus for that event.   While I don’t miss most of the features of modern cars, I do very much appreciate cold A/C and these condensers really help.  I won’t know until it gets hotter, but so far I am happy with my W123 air conditioning upgrade.

While I don’t particularly notice it when driving, it is apparent when the compressor kicks on when the car is idling.   The compressor is probably using a decent chunk of the power the OM616 makes at idle.

It is a complete bolt in kit so I could go back to original at any time.  I don’t plan to though. I have kept the original one to go with the car.

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Back in 2022, I fitted an upgraded A/C condenser to my 560SEC.   The A/C in that car wasn’t too bad, but the parallel flow condenser made all the difference.  From what I read, this is car more effective when using R134A.

The company that supplied the W126 condenser, Klima Design Works, have just released the 107 version.   This presented an opportunity to finally give the 450SLC the A/C that it deserves.  The kit comes with the upgraded condenser, plus the brackets and lines that you need.   You need to supply your own drier.

I supplied the kit to my mechanic to do the work.   From what I gather it was a bit more involved than the W126 install, probably because space is tighter on the 107.   During the install we found a hard line was missing.  While the line was possibly lost during customs inspection, Klima sent me another at no charge with very fast shipping, which I appreciated.   The kit bolted together well, the only slight issue we had was an existing A/C hose was a tiny bit short, and we had it remade.  Not sure if this was a RHD thing.

In any case, the difference is really noticeable.   While it wasn’t a very hot day when I picked the car up, I was quickly able to make the cabin too cold.   Even on not particularly hot days I was never able to do that.   I’m looking forward to trying it out on a really hot day.    So far I really like this upgrade.

While the new condenser is unpainted and the old one is black, once the bonnet is closed you could hardly tell.   I don’t want to paint it as it would probably loose some efficiency.  It is probably not an upgrade for a show car.  For a car like mine with 315,000km on the clock and used regularly, it is great.

While the car was in the workshop, it had all the bushes in the control arms replaced, and the front brakes done.  Some of the control arm bushes looked pretty bad, and the brake rotors had quite a lip on them.

I’m about to take the 450SLC on a 3,700km road trip.  This 450SLC A/C upgrade should really make a difference to how the car goes on that trip.   I’m also in the process of having the upgraded W126 condenser put on the 560SEL.

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While I had to do a few things to the climate control system, the A/C worked pretty well after being charged up.   The main issue was a leak from the compressor.   For a while, I was able to get away with charging it up annually, but recently it was degrading pretty quickly only a couple of months after a charge.    It was obvious that the leak was coming from there by using a blacklight.

Since I was already having the compressor changed out, I also thought this was an opportunity to try and upgrade I had been considering for a while.   Klima Design Works offer an uprated W126 A/C condenser that is designed for R134A.   R134A is not as efficient as R12, and this uprated W126 A/C condenser is billed as 30% more efficient than the stock unit.    That help restore the A/C performance lost through R134A.

I did some research on the various US forums and found good feedback from W126 owners in climates like Texas and Florida.   Basically the consensus seemed to be to either use R12, or this upgrade.   The upgraded W126 A/C condenser comes with the requisite brackets and hoses to interface with the W126 A/C system.   They offer two types depending on year and model.

Obviously, since I was having the compressor changed as well, I supplied a new receiver drier and TX valve to be installed alongside the compressor.   Like with my 300SE, I went with a brand new Denso compressor.   I’ve not had a lot of luck with rebuilt A/C compressors in the past, and given the high labour cost to have it installed, its much better to go with new.

While the car was in the shop, the front brakes were attended to.   On a recent brake pad change, I noticed that one piston on the front drivers side was not moving at all.   I ordered the rebuild kits, plus pads and a new set of front rotors.   My rotors were pretty crusty and within 2mm of the wear limit.   A good time to change them.   The rebuild kits were advertised as Bendix, but my mechanic later told me they were actually ATE units.   This was really annoying as I paid quite a bit more for these kits.

In doing the install, my mechanic told me that the fit of the uprated W126 A/C condenser was really tight.   This probably added a bit to the cost, but in my mind is a good thing as its using all available space for cooling performance.     There was also a little bit of interference between the secondary air snorkel on the 560.

The other issue he ran into during the install was the missing aux fan guard caused a rag to get sucked into the fan and damage it.   This was a problem with the Meyle auxiliary fan I installed a couple of years ago.   Since then, they moved to an improved design that does fit the fan guard.  I have that one on my 560SEL.   I’ve ordered one of these fans to fit to the car.

So far the weather has not been hot enough to really test out this upgrade.   We’ve had one day where it was about 25c and fairly humid and the A/C worked very well.   Better than before.   However, It was previously able to handle days like that.   The real test is when the temperature gets up into the high 30s and humid.

I’ll use this summer to see how I go.  If I’m really happy, I’ll also fit this uprated W126 A/C condenser to my 560SEL.   On really hot days the A/C performance is sub par.  A new TX valve would improve things I am sure.  However if this upgrade works really well, I may do it too.

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