300sdl Newbie - PeachParts Mercedes-Benz Forum

elhombre · #1 12-15-2004, 11:48 AM

Hi,

Just got a 1987 300SDL with 255k on the clock. It was an e-bay car that didn't sell, so I went up and took a look, and negotiated a price. The motor was rebuilt at about 200k, which seems odd, but there are plenty of boneheades out there, so maybe someone put gasoline in it.

In any case, I have a few questions and you guys seem to be pretty sharp:

1. At idle, there is about a 100 rpm surge. Constant and even--600, 700, 600, 700.

2. The oil pressure gauge on the dash pegs out at any time except hot engine idle, when it reads halfway (about 2). Is this likely to be the sending unit?

3. I'd like to help the tranny. It seems to be fine, but I doubt the fluid has been changed in recent history. I've heard from several sources that the 100% fluid change flushing system is bad for older transmissions, b/c it stirs up all the gunk, which is then redistributed throughout the system and can come back to haunt later on. Is there anything difficult about dropping the pan, cleaning, and replacing? Since I don't have a manual yet, would the correct procedure be drop, clean, replace gasket, replace pan? What is the torque spec for the pan bolts? Should I just wait til my manual arrives?

4. What's so important about a Mi-T-Vac? I mean, I have one, but so far the car runs fine without additional vaccuum. Could it help with mu surging problem?

Thanks,

Adam

Dervman · #2 12-15-2004, 12:18 PM

Welcome to the Forum Adam and congratulations on the SDL. They are great cars.

I can't comment about the lopey idle, but try doing a search here and see if something matches your problem.

The Oil Pressure Gauge sounds normal to me. Mine also reads max. except when hot at idle. This is a GOOD thing

I've never heard that completely changing the Tranny Fluid can cause problems although I would stay away from any additive cleaners. You will need to change the filter and (seperately) drain the Torque Converter for a complete fluid change. Again do a search for details. Many people have commented on the benefits of Synthetic ATF in their Tranny and I plan to change mine over at the next service.

Good luck with your new aquisition.

Brian Carlton · #3 12-15-2004, 04:52 PM

Quote:

Originally Posted by elhombre

2. The oil pressure gauge on the dash pegs out at any time except hot engine idle, when it reads halfway (about 2). Is this likely to be the sending unit?

3. I'd like to help the tranny. It seems to be fine, but I doubt the fluid has been changed in recent history. I've heard from several sources that the 100% fluid change flushing system is bad for older transmissions, b/c it stirs up all the gunk, which is then redistributed throughout the system and can come back to haunt later on. Is there anything difficult about dropping the pan, cleaning, and replacing? Since I don't have a manual yet, would the correct procedure be drop, clean, replace gasket, replace pan? What is the torque spec for the pan bolts? Should I just wait til my manual arrives?

4. What's so important about a Mi-T-Vac? I mean, I have one, but so far the car runs fine without additional vaccuum. Could it help with mu surging problem?

The oil pressure gauge is functioning normally. When cold, it will peg at 3.0 at idle. When hot, it will peg at 3.0 at somewhere between 1200 and 1500 rpm.

If you drop the pan and replace the fluid, attempt to drain the torque converter via the drain plug. It holds several quarts of fluid. I could not find the drain plug on mine and had the shop resort to a "flush" which feeds oil in and allows it to simultaneously drain out which, in theory, replaces the fluid in the converter.

The importance of the MityVac is to help diagnose any vacuum issues in the vehicle. It cannot provide "additional vacuum" during operation of the vehicle. It cannot help the "hunting" issue. The engine is not "surging", it is "hunting".

Pete Burton · #4 12-15-2004, 04:57 PM

Quote:

Originally Posted by elhombre

1. At idle, there is about a 100 rpm surge. Constant and even--600, 700, 600, 700.

When it's cold, hot or both? on the 617, surging idle while hot is frequenttly attributed to adjustment of the IP rack dampener

#5 12-15-2004, 06:19 PM

Welcome Adam, To begin with you've purchase a find car. Now the car probably needs your attention. I'm not sure how much you want to spend, but it might be a good idea to go to a respectable Indy in your area and have him evaluate your car for you. You'll probably spend some money, but it'll give you a starting point, and issues that you need to address. You can slowly but surely address the problems from worst to least. I went about a year on my car and then when things started going wrong on it, I then took it in. Well my Indy brought it to my attention about taking care of these cars. He told me that the MB can go along way even in bad conditions, but that sometime sooner or later you'll be stuck repairing major componets of the car. An evaluation of your car could save you lots of money later.

Hatterasguy · #6 12-15-2004, 10:19 PM

Welcome to the club, enjoy your new ride.

Keep the fluids clean and she will treat you well and last a long time.

Two things:

Never, never overheat it. It should never tun over 105c, read the 603 cracked head threads.

Also check the vac pump, when the old style fails it can dump its bearings into the timing chain causing the engine to self destruct. Look at the cover it you see 4 screws on it your in good shape you have the new style pump. If not you need to repalace it.

Now as to your questons.
1. It could be the electronic idle control. This is one system I know little about so maybe a search will turn up something.

2. Normal and healthy. Oil guage should peg when cold and when warm should be above .3 bar and peg to 3 bar by 3k rpm.

3. Change the fluid, I changed mine at 233k, it had not been done since 80k.

Smooooth · #7 12-16-2004, 04:21 AM

Welcome to the club...........

You've heard from a couple of the big SDL posters and there are a few more out there that haven't checked in yet......

And - most of your questions have been answered - except #1.

IMHO - Oil Pressure is acting normal. Flush tranny and TC as mentioned above. As a matter of fact - PLAN ON REPLACING ALL FLUIDS ASAP.

Be prepared for more age related issues and tackle them one at a time. The list is getting longer for me - buts it's a labor of love. Control Rod Bushings, Shocks, Alignment, Soldered Cruise Control and Climate Control modules,

Next on the list for me are Motor Mounts, Transmission Mount, Brass Fuses, Shifter Bushing, Etc.......

I hope we are not scaring you..........

Get some Diesel Purge and start working on the interior of the Engine.

Just to let you know - I am a newbie also - Just a couple of months.
Ask questions - these folks here are wonderful!!!!

*** BUT ***

You must learn how to use the search function!!!!!!!!!
You must learn how to use the search function!!!!!!!!!
You must learn how to use the search function!!!!!!!!!
You must learn how to use the search function!!!!!!!!!
You must learn how to use the search function!!!!!!!!!

Stephen

goldenbear · #8 12-16-2004, 01:01 PM

Adam,

Congrats and welcome. Here's my swag regarding your issues, in the order you listed them:

1. Injection Pump - mine did this shortly after I acquired it nearly 5 years ago. In my case, it was necessary to replace the pump. Hopefully, your issue won't be as serious.
2. Completely normal.
3. Don't worry, just replace the fluids.
4. Diagnosis of PITA problems.