'81 300SD possible purchase
 

Hello folks,

I'm Dave and this would be my first post here.

I'm looking into purchasing an '81 300SD(OM617 engine) with 297K miles on it for around $800. The vehicle was originally from Louisiana, so the body is solid save for the front bumper(rotted in a few small spots and will need to replace).

I've given it a thorough look over on 2 occasions so far.

Noticed a few things that bother me, and others that i'm looking for answers on before buying the car.

This is not my first diesel, and i know diesels well, but not so much in the MB dept. I've rebuilt many of the old GM 6.5s and 6.2s, and own one of each myself.

First off it starts right up after the GP light goes out. Smokes a good bit on the first start, like the injectors are leaking into the cylinders after shutdown.

The fuel has a strong sulfur smell to it so it's either really old, or possibly home heating oil.

The primary fuel filter is almost black so it is filthy. I know it has to be changed as does the secondary before any real miles are put on it.

The engine smokes blue a bit when running. Smoke smells like diesel, not oil. Do the injectors in the vehicles wear out like the ones i'm used to dealing with and end up with poor spray patterns and leakdown issues? What is the change interval, if any, on injectors?

It has a pretty bad valve cover leak so that will need to be addressed along with i'd say the first valve adjustment it's had in probably forever.

I can't test drive the car due to a leaking transmission line, and that it's not registered. I'm guessing the trans line was struck by something at some point because the line is not rusted at all yet it leaks from right under the injection pump area where the lines run to the radiator.

The engine seems to run fine at a fast idle and throughout the RPM range(in-operative tachometer so i can't be sure where it's running).

If the engine is revved hard it will give a good cloud of blueish smoke and then it seems to clear up.

My other question has to do with the timing chain. Do these chains have to be replaced at a set mileage?

I don't think this one has ever been done, but i can't be too sure.

The car seems to be well cared for. The trans fluid is nice and red and smells fresh, so someone has tended to it before i think.

The gas pedal is also busted. Where it attaches to the steel bell crank rod it is no longer attached to the pedal. the pedal is still attached to the floor however. This can be repaired right?

Other basic things are just from the car sitting.

Ign switch is a little sticky. Sometimes the car won't shut down until i mess with the switch. Other times i have to mess with it to get the blower to kick on. The car did sit for several years unused so i'm hoping it's just a sticky contact/vac switch issue.

Any help you can give would be greatly appreciated.

I just want to make sure i'm not buying a disaster.

Thanks everyone.

- Dave

From your post, it sounds like a car that I would buy at that price.

The Mercedes-Benz diesel in question is one of the best they ever built. That in-line 5 cylinder is probably the best of the best in the time it was built.

I never changed out the injectors on my '83 300SD in 16-years and 305K miles. I never had the valves adjusted, nor did I check or have the timing chain checked or replaced. Although I drove it easy (60 mph) over-the-road for years, I just drove it - A LOT!

The accelerator pedal inside the car failed on my car too at about 250K miles.

My transmission never gave me a lick of trouble. I changed it's fluid every 50K miles.

The car in question needs to be run and used. Clean up your filters, and run it! This is the best forum on the 'Net to learn from previous tutorials posts under 'search feature' and expert DIYER testimonials.

Fact of the matter is, I should have kept the car, but had new car diesel fever when I bought my sig car in 1999.

Well you are really going to have to get that car out on the road to find out what you need to find out. It has to be a winner at $800.00. Can't go wrong there. Hope you are correct on the rust. It is a southern car, probably has not seen salt, though stopped up drains, leaky window seals and AC drains that don't work and the moisture runs into the rear seat pans can be major problems. Pull up the carpets in a place or two, see what that metal floor looks like. Not stopping the engine when you turn off the ignition is probably a slow vacuum problem. There is a vacuum operated section that runs through the switch and is easy to work with. We would caution you to be very mindful of the ignition switch key tumbler part. If that thing is acting jerky like, they can lock up and give you a devil of a fit. You can easily pull and replace the tumbler so long as you can get the key to the second dot on the exterior of the switch. But they go from "bad attitude" to inoperative in a heartbeat, and just about everyone on the forum has to go through that with those sweet old Mercedes. And there is really only one way to do it. Pull the tumbler and with title in hand order a new tumbler and key from the dealer. The key will match your old key system. Listed under Diesel Giant is an excellent write up on changing out the ignition.

Injectors
 

As far as injectors go, if the vehicle previously ran on anything other than #2 Diesel for an extended period –– home heating oil as you say or WVO or WMO –– then the life of the injectors is considerably shorter, which, being a diesel guy, you probably already know. If this thing hasn't ran in over a decade, I would probably replace the nozzles and rebuild them anyway.

But first, do a diesel purge using some Liquimoly and change the fuel filters. Before doing this, however, you may want to see what style primer pump you have on the IP –– white mushroom knob, or black button –– because the older one (white knob) is known to leak fuel and air. You should replace it with the newer style black pump while you're purging and changing the filters. All those parts are on this website, which is also considerable help on myriad of issues.

good luck!

The blue smoke might be from bad turbo seals... a common issue, especially on 'Benzes that have sat for extended periods of time.

+1 on the turbo seals. very common. it could also be from timing issues, but that tends to be gray smoke.
in deference to Skid Row... I'd pull the valve cover, and check a few things. first, get a 27mm socket, and a 6" extension, and put a ratchet on the crank bolt, and rotate the crank clockwise facing the engine, until the cam mark on the front tower is EXACTLY lined up with the notch in the washer, and then look at the balancer marks and report where they line up.
next I'd get a set of bent wrenches and a set of feeler gauges, and adjust the valves. then if the marks line up, put a new gasket on the valve cover, and button it up lightly. *you don't want to tighten those nuts much**
next I'd take the air filter assembly apart, and replace any of the rubber mounts that are broken, then gently bend the tabs holding the oil seperator in the center of the air cleaner and clean it very well with brake spray, and then seal it back up with fresh ULTRA BLACK RTV. let that cure for a day. next look at the turbo inlet. is it SOAKED in oil? grab the turbine wheel, and lift up and down. it should have some play, but not enough for the blades to touch the housing. next push it in and out... it should NOT move at all.
if it fails either of these tests, it needs to be rebuilt or replaced.

oh... that trans line leak is also very common. there is a metal bracket that holds the lines in that spot... the rubber is likely LONG gone and the steel lines have likely rubbed through.
head to the parts yard, and snag another set from a junker. some have successfully coated them in JB weld, and covered that with a strip of metal. your call there. also, the dealer can get you new lines, and new rubber protection for the mounts.

another southern very little rust 250k+miles 300sd for $800 owner here. :waves:

oh, i run one of those glass inline fuel filters from the fancy hotrod section of the autoparts store and i keep a 3 pack of replacement filter elements in the trunk with a screwdriver. that way, i can see what's going on with the primary filter and i can pull over and swap it out in about 10 minutes if needed. you'll be doing that regularly for a while probably with that old fuel.

I would buy it in a heartbeat. even if it turns out to be rusty, you have way more than $800 in parts!
Do a Diesel Purge clean out and see if it helps. Run hoses from the injection pump and from the return line into a bottle filled with Diesel Purge and run the engine. You will be surprised at what ends up in the bottle...
I used to fill the bottle, plug the lines going to the tank, and then drive the car. I got about 20 minutes of running time from two cans of DP.

There is a vacuum switch attached to the key lock. If it starts leaking you will have a hard time shutting off the car. The shutdown is vacuum operated and the solenoid is on the rear end of the injection pump. There are posts on how to change it, the lock tumbler, do the Diesel Purge, etc on this site.

The 617 is a pretty bulletproof engine, not the smoothest or quietest Diesel out there but reliable...

As for the W126 body, it is one of the best Mercedes ever made. Parts are still available at reasonable prices.
Have fun and welcome to the S class Diesel family :D

for the dark filter, DON"T CHANGE IT!
put a bottle of Diesel Power CLEAR in the tank. let it slosh around for a bit, then run the tank out. it'll clear your tank, and filters.

The turbo has a little up and down play, but i've seen way worse. THe inlet of the turbo was not soaked with oil. The engine was down to the "add" notch on the dipstick, but the valve cover looks to be a really bad leak judging by all the dirt stuck to the oil on the head and down the block.

Oil pressure goes right to 3 bar when cold, and dropped to right around 1 3/4 to 2 bar at idle when at ~ 60*C on the temp gauge.

The smoke smells like un-burnt diesel. It burns the eyes if you get too close to the tail pipe, and i'm talking real close to get a wiff of it.

The engine starts very well, but will cough and puke smoke while shaking pretty violently. If i rev it while this is going on it clears up and runs better.

I'm wondering if i have a glow plug or two out as well as poor injectors.

I"ll have to check them next time i go look at the car.

Plan to pressure test the cooling system too. Most hoses appear to be original, so that's a bit scary.

I plan to try the diesel Purge treatment. Not really worried about the heating oil/old fuel in the tank. Home heating oil and older diesel fuels had much more sulfur in them, so they stank like rotten eggs more so than todays ULSD fuels.


Do the injection pumps on these engines go bad from sitting? My 6.2 K-5 Blazer needed an IP after sitting over a decade. The pump had water damage internally and the engine smoked like an SOB. However the internals of the 6.2 pumps are not engine oil lubricated like the OM617 pumps are. The 6.2 pumps are fuel lubricated, so water in the fuel presents a very serious IP health hazard.

Speaking of water in fuel, i've noticed this car doesn't have a WIF warning light or any kind. I find that strange seeing how water in the fuel can ruin an injection system.


So far i don't think i've got much to loose with this car.

I know it needs a driver front ABS sensor. The wires are cut for some reason.

The Brake light is on, but the pedal is fine. if i hit the pedal the light flickers. Front fluid level appears very low so that's my light i figure. Hope it doesn't have some huge leak.

The light to the left of the Brake light is on as well. I"m guessing it's an ABS light? It's an amber light with a circle surrounded by what could pass for brake shoes.

High beam switch seems to be a little sticky. If i put the high beams on all the headlights shut off until i wiggle the switch, then the high beams will come on until i touch the switch again. Guessing either worn contacts or it's sticky from age.

Thanks for all the help so far folks.

These cars of '81 don't have ABS. My '83 didn't. I could lock-up the front wheels at-will, esp. if someone pulled in front on me. That light may be the parking brake ON light indicator - or the front brake pad worn sensor, as I recall from my '83 300SD. New front brake pad sensor wires are pretty cheap at the MB dealer. They just plug-in very easily. I sus pect your brake light issues may all be related to the sensors. It sounds like you have one or two glow plugs out.


.

Brake pad sensors.

abs light will say ABS... unless you have a giant spider of brake lines in front of your master cylinder, you don't have ABS. the fluid level being low will trigger a red BRAKE light. keep in mind, you have two sections to the master cylinder, and it's sometimes difficult to see the rear one's level.
as mentioned, the yellow light with the broken circle is for the front pad sensor that is apparently cut on your vehicle.

You can see the ABS when you open the hood. It is on the driver's side above and behind the glow controller. 85 was the 1st year with ABS for the SD.

Get ready to spend some money. There will be lots you don't see. $800 is cheap enough but I'd try for $500 because of cost to repair. Brakes, rotors, calipers, suspension, shocks, seat refurbish, injectors, turbo all take either money or time or both.

I have what will be a parts car because better can be had for less than the cost of parts. I'd sell it if someone gave me $600 which is what I have in it.