The SDL showed up as an SD! - PeachParts Mercedes-Benz Forum

ahuggard · #1 09-21-2007, 01:10 PM

I was recently given a 1985 300SD (my father-in-law had told me it was an SDL, which is why I was confused when he called it a 1985 model . . .) and it was just shipped out to my house. I plan on getting PPI--although technically it will be a Post Given Inspection--just to get a baseline on what is needed for the car. It has some rough spots and some bright ones and my goal is just to have a daily driver with some character (no, I don't want a Honda Accord).

Right now, my main question revolves around oil pressure (yes, I did a search but couldn't find anything apropos). When the car is started the gauge goes right to 3 and stays there at idle. It also sounds like it is knocking a bit. From my old VW experience (67 bus, 68 ghia), my first thought is a desperately needed valve adjustment. What do you experts think?

Thanks in advance,
Alex

1985 300SD

TX76513 · #2 09-21-2007, 01:19 PM

First off if its a SD (5 cyl) a valve adjustment maybe a good idea - if it's an 86/87 and is a SDL skip the valve adjustment idea.
Diesels can sound odd to a person whom has not been around them. You make mention of the Vee Dub - have you been around diesels?

vstech · #3 09-21-2007, 01:25 PM

the sound of a 617 (that is the model of the engine in your car, 617.952 actually) at idle should be described as a low frequency rattle... if you hear any hard banging like a hammer hitting a steel pipe, you may have a problem, otherwise, normal tuneup should be fine. look for leaks in the cloth hoses that run between the injectors. look for oil leaks on the valve cover and around it's perimeter.
lets get some pictures up of your new 85SD
as far as oil pressure, does the gauge go to 3 before you start the car? if not then you are ok, these motors have outstanding oil pressure. what you want to look at is AFTER you have been on a good long drive when the motor is good and hot, what is the oil pressure at idle? 2? fantastic!, 1.5 average, less than 1, you may be looking at problems.

ahuggard · #4 09-21-2007, 02:32 PM

This is my first diesel, but I'm pretty sure it is not a "normal" diesel noise. It sounds more like a banging (really loud knock). Thanks for the quick replies! I'll try and get pictures up as soon as I can.

Alex
85 300SD

Mike D · #5 09-22-2007, 07:39 AM

To eliminate the possibility of "fuel knock" when the car is running, loosen the injector lines one at a time to see if the knock goes away or greatly lessens. Be warned, this can also make the sound of a rod knock go away (the lack of the fuel compression reduces the vertical stress on the rod bearing). Either way it will help you diagnose which cylinder is causing the noise.

vstech · #6 09-22-2007, 05:52 PM

also, if you find the noise isolated to one cylinder, swap that injector to another pot. see if it moves or not. if not, plan for a rebuild...

ahuggard · #7 09-22-2007, 08:24 PM

Thanks for all the insight. I will check those options out hopefully this weekend or the next. I'll get some pics posted as soon as I can find my camera.

Alex
85 300SD