How to convert a GAS W126 to diesel, the definitive thread hopefully.
 

Hello Mercedesshop, I don't post much, as you can see by my post count however if you see the number of diesels i have owned, I do know a thing or two about these cars.

Every year there is a couple of questions can I put a 617 into a 560SEL or whatnot. Hopefully this thread will answer those questions. I have done an 83 300 SD drivetrain into a 85 500 SEL, and another 83 300 SD drivetrain into a 82 380 SEL, and I am currently finishing my definitive swap, a 85 300 SD with a 4spd manual into a 84 500 SEC euro.

Its a big post so im not 100% sure where to begin, but I'll start by saying, you need to have both cars, Doing it with parts is gonna be a nightmare.

Lets start with the vacuum system.
You need to swap ignition switch because the diesel has a vacuum shutoff on it, it is pretty easy to do, but if its your first time its alittle tricky.
Along with that you run 2 vacuum lines into the passenger compartment. both go to the vacuum shutoff, one goes to a vac source the other goes to the IP.
The rest of the vacuum system from the diesel swaps over easily.

No if you are doing a 500 SEL or 500 SEC you do not need to worry about SLS, however the 560 SEL/C does so you will need to use a 617 from a 300TD or source an alternate pump.

Now the cooling system, Everything from the diesel bolts up, no problems here at all.

Transmission, you have to use the diesel trans, and its wiring is the same, you need to use the driveshaft from the gas car, and change the rear output yolk from the gasser to diesel. its pretty easy but requires a special socket, (30 or 31 mm longshaft 12 point socket)

Differential, no need to change anything here, the 2.47 in the gasser works very well with the diesels powerband.

Fuel system, Remove the electric fuel pump and filter and run the lines up to the front, (one for supply and one for return) no need to change tanks or anything, (you may go threw filters pretty quickly while the gasser tank gets degumed from the diesel). Make sure you swap over the diesel vent line.

Engine mounts, Everything lines up correctly here except for 1 engine shock, either live without it or weld a small braket on the kmember.

Now for the electrical.
Swap the alternator from the gasser to the diesel remembering to change the pulley from the one belt to the 2 belt pulley, (gasser is 85 amps diesel is 65 )

Note on the gasser which wire is for oil pressure and which wires control the coolent temp sender for the gauge and for the fans.

Connect those wires to the senders on the diesel engine.

Glow plug wiring, there are a few ways to do this, I choose to run my gp relay with a switch rather than the key, but thats just me, the gp relay has 4 wires to control it, Supply 12V to the red wire, and ground the brown and it will trigger the plugs.

Throttle, need to use the throttle from the diesel, everything bolts up.

That is basically it, its very easy, because everthing bolts up with very little custom fabbing. you will need the odd connector here and there.

You will not notice a big difference in the weight of the car, so you should not need to do springs. The diesel with a 4spd standard is considerbly lighter than a 500 SEC motor with auto.

Great write up. I guess this also means the easiest alt swap is to use the gasser's alternator instead of having to modify the system for one out of a SAAB.

Agreed. I almost bought the 85A unit for a 380 when I needed to replace mine, but it was a lot more expensive than a 65A....so I just went with 65. My original was a 55 though, so I did gain some improvement in having a strong 65 over a dying 55A.

Cool! Thanks!

Great!

Now, when can You come to Chicago? :)

need a donor car....
 

Okay. So, I have the perfect GASSER, just need a diesel donor car. Am I the only one that would need wife's permission before beginning such a project?:D

Nope. ;)

I am no longer married.
 

I swear, I'm on the verge of putting my precious (om617) in a gasser body. I'm seeking a 'friend,' who will loan/rent a space where I can do this.

I intend to clear all the attachments to the 380 engine and transmission before I move the gasser from it's storage so that pulling the engine and transmission will be a matter of unbolting the transmission cross member and motor mounts.

I will drive the diesel to the site and detach the engine and transmission, lift it out and bolt it in the gasser body. I will immediately move both cars and all parts to another locations. One car for storage, dismantling and parting out and the other to make a complete car.

I hope to move the diesel engine and transmission in a single day. I would give the low mileage (100K) 1985 380 engine to anyone who would furnish a space and help me make the change. It needs a(nother) fuel distributor. It has a new chain and the latest metal chain guides. I have a ton of relays, idle boxes ignition parts that go with the 380 engine.

I lucked out. I found a guy with a big garage who is a widower so no women will get involved. Turns out I have a tiller engine he needs badly enough to cooperate with me on the diesel swap.

What is the market like for a 380 engine and whatever transmission came in the 1985 380SE?

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What is the market like for a 380 engine and whatever transmission came in the 1985 380SE?[/QUOTE]

Not much, but you will probably sell the transmission

Too bad. I did a valve job, installed a new timing chain and all guides including the lower guide. I put a new tensioner and the tensioner guide on it too. I drove it for less than a year after the work until I bought the 84 SD. After that maybe I've put 500 miles on it.

I considered keeping the transmission. Seems it will fit the rear of that 617 nicely.