91 350 SDL Questions - PeachParts Mercedes-Benz Forum

beerme · #1 05-01-2003, 09:52 AM

I am very new to the Mercedes Automobile. I am a die hard Chevy guy that just traded his last Chevy for a Ford so you can see I know nothing about Benz. My wife had to have this 91 350SDL so we bought it. The car is beautiful but had many hidden "value add items". Currently the car has 128k on it and I thought was running well. It now is using a quart of little more than a quart of oil every 3k miles and runs very rough and smokes a lot when it is cold, is this normal behavior? The a/c isn't working (doesn't blow cold), the radio is now not working and finally my wife broke a headlight lense cover last night. So here are my list of questions, first I have heard that the 350 is known to have engine issues, can anyone elaborate on that? Secondly is the a/c using R12 or R134 and can a regular a/c shop charge the system as no resonable dealer in the area? Next is there an easy way to remove the stereo? Finally, what is the correct name for the cover that goes over the fog light (so I can search the internet for that part)? All help/advice is greatly appreciated. Thanks in advance, Sincerely Phil Lambert

sixto · #2 05-01-2003, 03:19 PM

Use the search function on terms like 350SDL, 603.971, bent connecting rods. Focus on posts by member JimSmith. In fact you might send him a direct message. You know where this is going.

The factory fill for your AC is R12. It has a conventional refrigeration system for AC. The vent controls are a different matter.

To remove the radio, pull out the ashtray, lift out the receptacle, remove the two screws, pull out the ashtray frame, get a hand on the back of the radio and pull it out.

It's not easy to fit an aftermarket radio because there are no speaker connections and no antenna lead in the dash. All that stuff is in the rear.

The headlamp or headlight door is the trim piece that includes the fog light lens.

Sixto
91 300SE
87 300SDL
83 300SD

300SE1993 · #3 05-01-2003, 03:28 PM

I once had a webpage that went into details abotu problems with these engines. Does anybody have it for this guy?

Basically from what I remember, these 3.5L engines were prone to failure due to engineering defects. Most fail under 100,000 miles but I have heard of one lasting as long as 160,000. High oil consumption and knocking are signs that the cylinders are becoming out of round due to one or more rods being bent.

stephenson · #4 05-28-2003, 06:52 PM

Hi beerme,

Welcome. There are several posters with 3.5L diesels ... some have had problems and replaced/rebuilt engines and some have been lucky (me).

Mine has 142K on it and runs very well. Nice car in every regard - as long as I can fix it .... very expensive at times if you are having the work done.

Change oil to Mobil or Delvac 1 and see if it changes anything. My understanding is that the oil burning gets very, very bad ... a quart a day! Do a search and you will find a lot. I removed intake manifold and found huge amounts of gunk ... clean yours all up and see what happens.

While I have not swapped my radio, yet, my understanding from the many posts (do a search) is that you can replace radio with aftermarket by running speaker wire from radio to behind back seat (where amps are) and splice into the radio wires there going from the amps to the speakers. Takes 4 pair, I think.

Good luck - keep us posted.

fz500sel · #5 05-28-2003, 08:26 PM

and it runs great (knock on wood). I have only had it for the last 6 months but it has run great so far. it doesn't appear to use alot of oil either. I have been fixing problems but they are not engine related. I just had all of the o-rings and gaskets replaced for the injection pump cuz it was leaking. Also I had to replace the sepentine belt tensioner shock, but I have heard this is a common part that needs to be replaced as the bushing wears out in it.

I have to fix a camber problem in the rear and I was told that it is gonna be real expensive.

Any ideas on how expensive this could be?

sixto · #6 05-28-2003, 08:35 PM

Trailing arms are almost $1200 each from FastLane. I'd look into a used one. I can't imagine what a new subframe would cost. But I'd also check for a used one.

If you're sure the only problem is camber, install a shorter spring on that side

Sixto
91 300SE
87 300SDL
83 300SD

beerme · #7 05-30-2003, 10:21 AM

Update to my first post. First thanks to all that have responded your advice and insight is greatly appreciated. I had the a/c charged by a local a/c shop. That seems to work well but the def/dash vents work intermittently. What I mean is it will bounce from the def to blowing out the dash vents and then back. I am guessing there is a vacuum problem somewhere but not sure where. I don't think it is in my dash though otherwise I would think the dash would never blow. Secondly I have an oil leak somewhere up front. I am unable to find it but at the moment, this weekend hopefully I will locate the source. I have heard that these engines are known to "weap" around the sending unit, can anyone verify that? On to the stereo, I replaced my factory unit and had a fun time finding the amps and tuner. My new head unit is a sony and was a direct fit into the dash. Wiring was another story but I figured it out. biggest problem here is I couldn't figure out how to get the cables under the carpet so for the moment it looks very amaturish from the back seat. Finally I have a massive virbration in the front end when I brake, I think it is a warped rotor. So I bought rotors and pads, the question here is how do you get the rotor off? I took the wheel off and couldn't get the caliper off though that I can figure out. Muscle power is the answer there I think, but the rotor has a reverse bolted plate on it. No clue where the bolts are or where the are accessed. Any clue here is much appreciated. All in All I am quickly becoming a W126 fan, the car runs great and is very comfortable to drive. Thanks again..........

sixto · #8 05-30-2003, 07:15 PM

AC - the center vent actuator is probably starting to go. You can get a replacement diaphragm and replace it without pulling the actuator. Pulling the actuator is quite a chore because outside of the very recessed attachment screws, the far end of the actuator arm that attaches to the lever that controls the flow of air to the vents is really deep in the heard of the dash. I could barely see it let along figure out how to disengage and re-engage it.

Brakes - there are two bolts that hold the caliper to the knuckle. If those bolts are off and you can pull the caliper, your rotors are probably worn to the point that there is a ridge holding the pads in place. I'd rip the pads out of there by any means. The caliper should coe off easily with the pads out.

The rotor comes off attached to the hub. The bolt heads are on the back side of the rotor so there's no cheating - you can't pull the rotor and leave the hub in place. You'll have to decide whether to top up the grease or clean and regrease the bearings before putting it back together.

Sixto
91 300SE
87 300SDL
83 300SD

beerme · #9 06-01-2003, 08:35 AM

Is there any special you need to do when replacing the fuel filter? I am guessing the introducing air into the fuel system is going to cause a problem. Just curious if there are any procedures I should follow when replacing the secondary? Thanks in advance for any responses

tjohn · #10 06-01-2003, 09:24 AM

Brakes - see forum member Thomaspin's web site.

He's a got pictorial walkthru's of a lot of common 126 jobs; you'll need to do 'em sooner or later if you're a DIY guy.

On the fuel filter, I believe that unlike my car, the OM603 is self priming, just fill the cannister up w/ diesel or a fuel additive before replacing it.

t walgamuth · #11 04-19-2005, 06:46 PM

the rear a frame may be bent. i think that they may be the same as on the 123. if so i bought my last two from a small local yard for i think $75 ea. they took it off with the hot wrench. my local shop charged i think about $300 to install. on my cars one got bent by my daughter sliding on ice against a curb. the other rusted until it began to collapse. the wheel was in about 3" at the top and the whole shebang was about to fall off. this one was on the 83 240 that i sold to my son and his wife. she was driving and noticed that the hubcap fell off and didn't notice the wheel leaning over! on your car, as new as it is, i doubt it is rusty, hence suspect it is bent. good luck.

there may be no reason to panic on the engine. rough running can be caused on start up by one or more bad glow plugs. a little difficult to get at but not a huge expense. the bent rod scenario will make drastic noise and severe oil consumption. it doesnt sound like yours is that drastic.

t walgamuth · #12 04-19-2005, 06:55 PM

ps
the oil may use up faster if you arent changing it often enough... also be sure to use diesel rated oil. i like the rotella but some guys are using mobil one. be sure to check the manual for weight recommended. i always err on the side of using heavier oil especially in an engine with some miles on it. i use 15w40. i find if i run the oil over the 3,000 mile mark very much the engine will go through it faster. oil air and fuel filters are more critical on diesels in general. dirty air filter will damage diesels much faster than gas engines, ditto dirty oil. a plugged fuel filter will cause loss of power gradually. if you get water in the fuel you might grow algae. this will show up as small black dots in your primary (the smaller ) fuel filter. it will plug up the works. but you can buy algae killer at a truck or tractor supply and it will kill it and un plug at least the sock in the tank pickup.

too much info? if so sorry. good luck.

diesels forever!