newbie with questions
 

I just purchased my first benz last week. A 1985 300D 5cyl turbo diesel. What is the redline on this engine? The only way I can get up to speed on the metered on ramps in milwaukee is to manually shift it and I really dont know how high this engine is supposed to rev. I bought the car on E-bay for $1800. The interior is very clean, even the driver seat is good. The power antenna even works. The car frequently blows the fuse that works the radio, interior lights, antenna and hazzard lights. Is this common? Anything I should look at? Maintanance wise I changed the oil, filter, both fuel filters and air filter. Anything else I should do right away? I converted the air to 134A and after about 10 minutes of being on i here a scraping noise under the hood, it still blows cold, any ideas? Taking to a dealer is not an option for me $$$. I buy older rear wheel drive cars i can work on.
Thanks for any help,
Ken

Ken,

Welcome to the site. How many miles on your new Benz? When you do this acceleration event, does the car smoke a lot?

It seems you are taking care of the routine things. You should also check the valve lash or gap as these engines are sensitive to this dimension. As the engine runs the valve kind of pounds its way up into the head and the gap closes. This can lead to hard starting and poor power. Also, there is a turbo charger on the car that has an output pressure regulator with a connection to the fuel injection pump. A Diesel needs more fuel to make more power as it always gets a full charge of air (no intentional throttling of the intake volume). So, there is a means to sense intake manifold pressure and let the injection pump know it should add fuel per injection squirt the higher the pressure goes. This system is susceptible to being clogged with the exhaust particulate and other stuff, mostly due to the exhaust gas recirculation system and the blowby gas induction system.

The car should smoke somewhat on hard acceleration, and the engine performance should be noticeably stronger as rpms climb above 1,000 or so. If you get no smoke, the chances are the injection pump is not getting the signal the turbo is putting out extra air. So, you don't get a boost in performance.

Additionally, a bunch of stuff works off vacuum. As noted, Diesels don't make vacuum very well, at least not on purpose, so there is a vacuum pump to create the vacuum. The brakes, transmission, door locks, shut off valve for fuel to shut down the engine, air conditioning system and so on, all depend on the vacuum system. As the car gets old the lines, especially the connectors that are made of rubber, fail. This makes the vacuum system weak. As it fails to provide vacuum all these other functions begin to fail in wierd ways. It is not that hard to figure out and fix though and the parts are not too costly.

So, do a search on "Alda" (the intake manifold pressure compensating feature on the injection pump), or "banjo bolt" (the connector you clean where it comes off the intake manifold), and "Vacuum System" and you will find these things come up all the time and others have donated many hours of their time to teach us what they learned on the subject.

Good luck and enjoy the car. Jim

147,000 miles on it. When i get on it I see windows roll up behind me (yes it smokes fine). The only vacume related problem is that the central lock system described in the owners manual dont work. are all equiped with these? The brakes work beyond excellent. I have driven full size olds and buicks all my life and man this thing stops. I thoght my 94 buick roadmaster had good brakes. In a couple weeks i will attempt to adjust the valves, can this be done with american feeler gauges or do i neet to find metrics? Rust wise the car is fair, some rust in wheel wells and jack points but none in shock towers.

Ken

once you do a valve adjustment you will notice a big difference in car's overall speed and acceleration........

Wodnek,

First, all W123 cars came with vacuum locks. If yours do not work at all and the rest of the car's vacuum operated items are working, someone has sealed off the door lock system. That is ok, and the car will work fine. If you want to have the system back, you need to use a vacuum tool to find the problems. The parts are nickel and dime for the most part, but there is some work here and there. Like taking the door interior panels off and so on. Not hard work, but if you are like me, I usually end up breaking some old plastic parts along the way and the job gets bigger before it gets done.

Any feeler gages are fine, although English units will not get the precise gages. Instead, adjust them a little loose since they will close up over time. I find a bigger clearance in Winter helps winter starting.

Always replace the vavle cover gasket when you do the valves, by the way. I usually take the car to a car wash and blast the engine around the valve cover to head joint clear. Makes the job go a little faster. I also use a very stiff synthetic grease (such as for disc brake parts that comes in a small squeeze bottle from NAPA) to seal the valve cover gasket to the valve cover and head. It helps fill in the small gaps that will let hot synthetic oil seep by. Do a search on the subject and you will find lots of helpful data, kind of "Virtual Experience" for the DIYer.

Good luck, Jim

Welcome to the forum.

Here is an online service manual that is very helpful.

http://skinnerbox.steaky.org/123_DISK2/program/123-cd-index.html

The redline of the car does not really matter. The injection pump will not let you overrev the engine.
The 1,2 and 3 yellow dots on the speedometer are the maximum speeds for that gear. so if you want to manually downshift don't do it if above the max speed for the gear. Actually the tranny won't let you do it.
Your first Mercedes 300D. YOur car may be operating and driving normally. These are a different beast to dirve than any American car you have driven. First your turbo gate does not open until 2000 RPM. So you will notice this boost at 2000 RPM. MAKE the car shift to get the engine in the 2000+ range. You pedal has a downshift switch. Satrting at a light I floor the pedal. As the rpm's incresase I may let up opn the pedal but not much. This will be the first car that you dirve where you floor it all the time. If at speed and you want to accelerate, press the pedal to the floor and force the "downshift swithc" to downshift the tranny. Dont' be afraid to drive the engine hard, they like it. As I said you want to keep the enigine in the 2000-4000 rpm range for best acceleration.
If you wonder if it's driving normal. Take it to a dealer and ask them to drive it, they won't charge for this and they can tell if it is fine. Or join the MBCA (Mercedes Benz Club of America) go to a meeting and ask one of the members to drive the car.

My recomendations.
Change the oil and filter every 3000 miles. Use the Mercedes, Hengst or Mann filter. Natural or synthetic, your coice.
Adjust valves once a year. Twice is better.
Use a algeacide in the fuel 2 times a year.
Check the vacuum system completely all connectors and actualtors. Review the systems in the online manual, buy a hand pumped vacuum guage. Vacuum controls the following
door locks, brake booster, tranny shift, EGR operation, engine shutoff, injection fuel control.

Keep searcing this forum and the manual, then ask questions, 99% of the questions have been discussed so a search is the first step.

Check your flex disks, Item 41 propeller shaft. If the fron one breaks it could total the car.

Blowing the fuse is not right. Mercedes usuall don't blow fuses. You need to fix this.

Converting to R134A Unless you flushed the system and changed the seals to R134a seals your setting yourself up for a system failure. the R12 oil must be removed. The R134a oil and R12 oils dont' mix so you dont' get correct compressor lubrication which leads to compressor failure. Do a search on this one. DON"T go withtth efreeze 12 or andother freon but R12 or R134a. You will have a problem finding a shop to work on the system if you use another freon.

Dave

For the transmission shifting issues make sure that the bowden cable is adjusted correctly. If you're wondering what it is, just do a search on it. The adjustment is very easy to do on your '85.
Also check out http://skinnerbox.steaky.org/ . It's a great online reference for yor MB.

Thanks everyone for your tips and answers so far. I went ahead and adjusted the valves today. I have a chilton manual and it listed .004 thousanths for intake .012 for exhaust. I found 2 valves loose and the rest tight by .002 to .005. I have not had it on the highway yet to see the difference. The valve adjustment took me 4 hours, I used a 9/16 tappet wrench for the bottom nut and a 14mm combo wrench for the top. Except for the 9th valve from the fron it was a piece of cake. Ill get a 14mm tappet wrench for the next time. I love how the hood opens 90 degrees.

Ken

Another question i have...
I have always used power peformance in the white bottle for my powerstroke diesel. In my 3 tanks of fuel so far i have added it to my MB. Is this good for these?

Ken

Wodnek,

Many of us use that stuff regularly. Shouldn't be a problem. I also use RedLine Diesel Fuel Catalyst. Both help with avoiding "nailing" and other poor combustion issues. Good luck, Jim

dmorrison,

Where can I get biocide in NE PA? I looked in a new catalog from Performance Products and its not in there any more.

I tried a lot of truck stops from here to AZ and FL and couldn't find any. Tried some local marinas, also no luck.

P E H

What he said, if your not flooring it daily your probibly not driveing it hard enough and building up carbon. Diesel or not, they like RPM. I'd be afraid to trust the governer to keep it from over-reving, or the trans, but there not *suposed* to let you.
I know with the shift lever in 1st mine will shift to 2nd on it's own anyway with enough RPM. Learn the feel of the shift gates and beware there is no safety lockout to keep you from nuatral or reverse other than the gates.(which is a fine thing in my opinion).

Welcome to the forum. I had the same problem with that fuse. I found my interior light was causing the fuse to blow. turn off the light at the switch, right next to the light. see if that stops it from blowing. there is a plastic insulator up in the light assembly that gets old and falls apart. tape it over and move the wire so it doesn't hit anything. should fix it up. Good luck. let us know how it goes.