Mercedes-Benz 300SD One Year Report

After driving my Benz every day for about a year now, I’ve grown accustomed to its spaciousness, toughness, and reliability. Like no other vehicle I’ve driven, this car is truly an engineering success for the folks in Stuttgart. I feel it’s appropriate at this time to mention some of the highlights of my Mercedes-driving experience as well as important to-do items.
  • Listen to your Benz. Over time, you’ll learn to distinguish between the sound of a hot and a cold engine, a wet and a dry engine, an engine that needs oil, coolant, lube, purge, or a valve adjustment. Knowing how your car sounds is pivotal to determining what it needs or will need.
  • Take care of your Benz. Don’t ever skip scheduled maintenance, and the car will thank you by never dying. Well, that’s a stretch, but it will last a really long time. Wash it, lube it, and fix even minor problems. An oil change takes 20 minutes and can be done in Wal-Mart parking lot with some Shell Rotella, a wrench, and a filter; all can be bought at your local AutoZone.
There are certain quirks that can be attributed to this particular model. For instance,
  • The gas pedal might need to be depressed when cold starting. After a few seconds of hovering around 15 on the tachometer, the car will idle normally.
  • The automatic transmission has “sweet spots”. I’ve learned the best places on the tachometer to shift gears by playing with the gas pedal. I know it’s true because when an unaccustomed person drives it, the car shifts like hell – jerking, knocking, etc.
  • The smell of old, moldy ass inside the car can be attributed to rotting foam under the carpeting. Some tell me to grill the carpets in hot sun for a few days, but my mechanic suggested buying a Yankee Candle air freshener. Come one, the car’s over 20 years old, don’t be so picky.
  • The shag carpet will get dirty and you’ll have to steam-clean it on a nice hot day, allowing for plenty of drying time.
  • You will have to plug the car into the grid on cold winter nights. The benefit – almost instantaneous ignition. I wouldn’t keep cranking the starter for more than 10 seconds. If you press gas pedal too hard, you’ll flood the engine with cold diesel fuel. Of yeah, you’ll have to add cetane booster/anti-gel to your fuel.
  • The rear or side air filter housing mount will break due to a design flaw. The engine’s vibrations will always break one of the mounts, so one day your car might shake a bit more than usual.
  • The smell of diesel fuel inside the car can be caused by leaking return lines on valves. Don’t take it to the mechanic, buy some cloth-wrapped lines, pull old lines with needle-nosed pliers, and put new ones on. The last line is a dummy; it’s plugged with a metal pin.
  • The breather hose on top of the air filter housing and valve cover will leak. Don’t worry, it’s normal, just wipe it once in a while.
  • You’ll have to regularly inspect hoses and check for leaks.
  • You will have to adjust valves every 15,000 miles. The process is not complicated, but it takes time. If you get annoyed by doing the adjustment, SELL THE CAR TO SOMEONE WHO WILL APPRECIATE IT.
  • Rear window will probably develop a leak, causing water to sit between layers of glass, in turn causing “fogging”.
  • If your heater starts blowing ice-cold air, replace the monovalve assembly – the rubber membrane tends to break, causing coolant leaks.
  • The car has more power than you think. The "iron five" under its hood doesn’t make it a racer, but the turbo gives it some serious pep. I’ve never had trouble passing anyone on the road. That doesn’t mean a crappy Impala can't kick my ass speed-wise. You will not win any kind of speed trial with this Benz, but you took the reliability/longevity tradeoff when you bought it.
  • The car’s favorite cruising speed is 65 mph. I go 73 on a freeway no problem, but based on the sound and the feel of the car, I have a feeling it “likes” to go 63-65. You must not push it faster than 75. Firstly, there’s no need to go that fast. Secondly, it wasn’t built for speed, so don’t be a dumbass.
  • The electrical items in the interior will break. Over the course of owning this wonderful car, you’ll end up fixing windows, locks, switches, lamps, the odometer, the seats, etc. Those are items with intensive use, so it’s only natural they break.
  • Small mechanical parts will break. You will end up tearing into the doors and wondering why a company as awesome as Mercedes couldn’t make the window slider inside the door out metal. Don’t get pissed off when a $3 white plastic slider ruins your Saturday. But then again, are you man enough to just fix it yourself?
  • If the car is starting to slow down stall and eventually stops like it ran out of fuel, check 1) how much fuel you have 2) the inline fuel filter. Chances are, the little plastic inline filter is plugged up and the engine is not getting enough fuel to burn.
  • If your Benz has an aftermarket alarm installed, get ready for some fun - those alarms are known to go off for no aparent reason after, oh, I don't know, 15-20 years. Disable the alarm by taking out the floor mat on the front passenger's seat, then taking out the carpet, then unhooking the plastic panel way in the back, and finally, by unplugging the sensor.
  • Odometer will break sooner or later. It's weak spot is a pressed-rubber gear that will wear out and fall off, causing your odometer to click. Fix it immediately!

I’ll just keep adding to this list when I think of something new.


Blogger reckless rogue said...

Mercedes Diesels of the 1980's were probably the best production vehicle ever made. Of course, you already know that. I have an '83 300SD, 213K mi. Of course, good preventative maintenance means that these 617 diesels can make it to 400K mi. before a rebuild. That is just remarkable!

I, too, love my Benz. When I get under the hood, I marvel at some of the complexities like the vaccuum system, yet some of the great simplicities of the 617 diesel motor. It truly is a great car. I'm glad I found your blog. I will check in often and see how you're doing.

1/06/2006 09:33:00 AM  
Anonymous Maxes said...

Thanks. Please spread the word about the blog, I'd like to turn it into a resource any 300SD owner could update.

1/06/2006 09:38:00 AM  
Anonymous Anonymous said...


You are brilliant man in getting this domain name! I wish this site would have a parts exchange section. It's been said that "one man's waste is another man's treasure" and we can apply it with our beloved MBs. I'm from the Philippines and most of the time, parts are so hard find specially for old MB models. But I think it should not deter us from keeping our 300SD's on the road (and other old MB models perhaps). I know there are a lot of people who are simply fascinated and in love by this particular model that we can start by helping fellow enthusiasts keep their SD's roadworthy. For example, recently my 82 300SD's wiper linkage broke. It cannot be welded (at least here) because it's an aluminum. Because of limited resources, I have tried looking for surplus but they wanted $300 for an assembly. My motor is working fine and I only need the linkage and will not pay $300 for it. My idea is if other people in other part of the world has this assembly with a broken motor and a good linkage, then they may be able to send it to this part of the world for the benefit of another 300SD in need of the part. If we can develop this kind of practice, maybe keeping our beloved 300SDs on the road AROUND THE WORLD will be much easier. Kudos and more power to your site.

1/15/2006 12:21:00 PM  
Anonymous Mercedes 300sd said...

Thank you for kind words. I think part swapping is a good idea. I'll definitely consider writing some code to facilitate that.

1/15/2006 12:28:00 PM  
Anonymous Anonymous said...

I'm new to the world of Benz - just bought an '84 300 SD and love it, but there are some issues to work out. The fuel guage and the odometer (main and trip) have both stopped. Nerve wracking not knowing how much fuel is left in the tank. Driver and passenger front windows don't move - tested the switches and they are fine. The trunk gasket leaks on the top corners and it is mildewy. Any suggestions for driveway repair?

Thanks much

1/19/2006 10:51:00 PM  
Anonymous 300SD said...

Listen to the odometer for clicking. If it is, chances are the little pressed rubber gear wore off. Speedometer.com for repair, about $200. Keep a little gallon canister with diesel in the trunk. Your mileage is safely 23-35 mpg, your tank is 20 US gallons, you can safely go 400 mi on a tank. GoogleMap your commute and divide into 400. Full up accordingly.

Windows - if switches are fine, it's the motors, have them tested and rebuilt. If motors are fine, it's the stupid little plastic slider. You'll have to disassemble the door for sure. A few hours, no biggie.

Trunk gasket - can't advice too much, use common sense. If it's worn out, replace, can't be more than a hundred bucks.

Sounds like we have identical cars. If you got more specific questions, I'll be glad to help.

1/20/2006 12:16:00 AM  
Anonymous erikc said...

Just bought 84 and love it. I have owned several new cars over the last 15 years and was overjoyed when I opened the massive hood and was able to identify the main components and actually reach them. Hose question and in need of help; 2" or more diameter hose that sticks out the front and loops back over itself into the base of the air intake/filter assembly. It appears the top section of hose is too short. I cannot get the hose and clamp over the ridge to properly clamp it down. I would like to find a web site with engine photos and designations or maybe get help from a reader who knows the name of that hose? Thanks for the great web site.

1/20/2006 10:18:00 PM  
Anonymous 300sd said...

Blogger stopped sending me comments for some reason, so I have no idea who is posting what and when.

Yeah, I'll snap some pics of the engine compartment one of these days.

1/30/2006 07:08:00 PM  
Blogger ExamMan said...

I am happy to find your blogs.
I just bought an 84 300SD
with unexpected problems.

The passenger seat belt buckle is not working. The right windows don't open. Someone tried to fix the left ones and did a bad job to the driver's window. It does open, but cannot close completely, leaving an inch. The plastics on the door open lever are broken. The wood trim on the left are broken. Someone didn't know how to remove the door panels. The rear left door panel was reinstalled incorrectly.

The car runs and the transmission seems ok. That's the consolation.
I ordered a buckle from ebay. And have to order the wood panels, and learn what's wrong with the windows.

The rear seats needed repair on the leather. That's a problem. I have to learn how to sew ?


4/27/2006 10:24:00 AM  

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