1986 Mercedes S123 230TE

I’ve had 3 cars with K-jet. All mid 80s VAG.

I like it. It just works and is actually really simple in principle. It does have a few foibles, which are mostly pretty easy to deal with. Does love the occasional pot of injector cleaner.

Saw a great vid on dismantling of it recently. Not suggesting you should do it, but gives great insight into how it works. Will put a link up when I’m at the PC.

The bypass valve can usually be washed out with carb cleaner or similar to remove the gak inside that is stopping the the sliding disc from sliding. Have one from a Mk1 GTi on my Vitesse and is still works great. Although they all look the same there are in fact many of them with different parts numbers and different characteristics.

Nick

Definitely useful data in there, I'll need to compare the specs to the Saab data one day out of pure curiousity.

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Not a huge amount to report today really but we've made some incremental steps forward since yesterday. Firstly I did some research and figured out where the idle speed adjustment screw was - exactly as I expected, this one:



Worth remembering that this was transferred over with the head, so not surprising it needed a slight tweak. I did make a very careful note of how far I moved it in case I needed to put it back where it started.

A bit of vacuum hose shuffling has restored the fast idle function when engaging gears too, which is nice as it makes me less paranoid that the car is going to stall every time I stop.

I'm pretty sure things aren't actually hooked up correctly, but I'll address that once I find a proper diagram. Finding a decent one that's not for a diesel has proven annoyingly tricky so far.

Horrible attempt at video footage from a test run...I basically decided to do this on a whim and just wedged the camera under the passenger headrest. This really needed to be a good 6" higher up as it kind of feels like you're a five year old trying to see out without a booster seat. Figured you can watch or not as you wish!



I will try to get something better at some point.

The horrible metallic "clank" from the back now and then is a five litre bottle of brake cleaner in the boot. I thought being wedged in place it would stay quiet...I was wrong.

Gives a decent snapshot of how the car is currently running - though the mic really doesn't catch the harsh engine note at the top end of the rev band. It starts sounding rough around 4k and gets progressively worse above that, so generally I am just trying to keep the revs down when I can.

Second (which the car moves off in unless you boot it) into third is a little harsh about 80% of the time, far worse when cold. Third to fourth though is generally beautifully smooth, only really noticeable from the change in engine note. That's what I remember generally being the case with Merc autos when they're behaving...lazy but very refined gearbox where you hear rather than feel shifts.

Had a decent poke around today and can't see any evidence of any fresh leaks of anything. Think at this point I need to get the next oil change done then give the engine bay another clean. Especially the front of it which I largely missed last time, so any future escape of oil is visible.





Also sorted the windscreen washer pipe hanging off the bonnet. That was bugging me.

Oh, and reattached this bit of trim that was shaken loose by the brutal gearchanges during the earlier test runs.



I wasn't kidding about how harsh the jolts were!

Oil change tomorrow, then we'll just cross our fingers and try to use the car as normal this coming week I think, and see what happens.

Next up will be pulling the alternator from the Jag to see if I can sort it...I was loathe to do that until the Merc was mobile again though for obvious reasons! Was really hoping I'd have a replacement here to just swap out...however Hermes appear to have managed to lose it, so we'll be checking the condition of the brushes first. Fingers crossed it just needs a brush pack - the symptoms definitely fit at least.

Cleaned up the area immediately around the SLS hydraulic reservoir, hopefully now the hose isn't sweating it will stay dry now.



Somewhere that *wasn't* dry I spotted while walking past the car when taking the dog out for a walk earlier was the offside rear corner.



I was initially slightly concerned that might be fuel (I know the tank does leak when absolutely full), but it turned out to be water.

Looking down into the area where the jack etc is stowed showed the source.



There was about 4" of standing water down there. Not screenwash either, so the rear washer bottle isn't to blame.

A bit of flailing around blindly I found what felt like a drain hole, and after fishing out some pond scum several pints (I'm not kidding, there was quite a lot) of water came pouring out.



Not entirely sure where that water had come from, but I'll definitely keep an eye on that. There's enough rust on this car as it is without it actively trying to dissolve from the inside out.

I'd hoped to get an oil change done today but just ran out of time, it'll be done tomorrow. Fluid check revealed everything still seems to be where I'd left it, despite the weep from the radiator.



I really do need to look at wiring in an override for the thermoswitch for the cooling fan, getting this far up the gauge before it cuts in just makes me way too anxious.



I think this basically stems back from days driving cars where seeing the gauge going anywhere north of half was bad news...a large portion of the gauge being the normal range just makes me nervous.

Agree with Rich. Most moderns are programmed to sit bang on the middle under normal operation, whereas the live data will be considerably different. I understand that being used to that, then jumping back into something retro can massively trigger anxiety, though!

Just to answer one of your questions, there is nothing wrong with it starting in second - a Mercedes quirk for comfort not speed!

Have you tried a fluid and filter change on the box? They're robust units and very very cheap to do a service on these days.

They are indeed lovely looking machines...

It looks like things are just getting better and better with your glorious machine!!

Superb!

Definitely on my list of "things you don't want to discover don't work half way through a journey" are windscreen wipers. Which I discovered today when I went to wash the windscreen on the S123 were indeed completely dead.

As they worked fine yesterday my first suspect was a dodgy contact in the fusebox. Which on these cars is on the bulkhead in the engine compartment behind this little plastic cover.



There's a knack to getting it in and out of the space around the brake servo but you soon learn it.





I've plenty of prior experience with this type of fuse as Lada used them right up to the late 90s, and about 95% of electrical issues on those can usually be resolved by wiggling fuses. This seems rather less temperamental as the fuse holders are of several orders of magnitude better quality (brass rather than rusty pressed steel for one thing!), but they can still be a bit twitchy. Sure enough as soon as I touched the relevant fuse the wipers sprang to life. To took that one out, cleaned the contacts and the fuse and put it back in. Hopefully problem solved.

Picked up a replacement for the mangled throttle return spring and a new PAS belt from the dealer today (previously picked up belt for that is the wrong size), and have also ordered a new heater control valve - meant to order that with the last batch but totally forgot. Dealer was a tenner cheaper than eBay there too.

Something else I think I need is the seal for below the cap on the SLS reservoir cap (the return line runs into the cap) as we apparently have fluid seeping out of there still, evidenced by the film on the lid of the reservoir.

My dads 240TD had dodgy wipers (just stopped midway through a swipe of the screen) and it was only about 4/5 years old when we had it in the late 1980's...

Made journeys in the rain fun!!

I think it was solved but I was quite young then so can't quite remember the ultimate outcome (probably just wiggling the fuses)!

That looks incredibly clean! Lovely colour too, definitely up there as one of my faves, though I still feel the white drew me to mine.

I did get the rear headliner trim sorted, my solution was to rough the back of the board up and to go over it with resin, as I had a heap on hand from the Invacar bodywork.

Seems to have worked as it's still holding it's shape.

This car is never going to be anywhere near as tidy as yours. Not even close...unless I win the lottery and can throw unreasonable amounts of money at a body shop anyway!

Being on a Y plate I imagine you still have the older style instrument cluster? That and the gear lever are the two things which look oddly modern in the cabin of mine being a 1986 car.

Do wonder how close to the end of the line mine was given they stopped making the S123 in 86. Is there any way to figure that out from the VIN or anything?