Lurking noobster outed...
 

Hey guys, and gals, just acquired a 1986 300 SDL from Alantbird here on the board. He's in Belen, NM and my wife and I are snowbirds in the Mayhill, NM area, 120 some miles NE of El Paso (we have a 50 acre hobby farm with an on-site wood-fired brick oven pizza restaurant in SW Wisconsin. If anyone wants to work 4.5 months, drive cars on the twisties in the Mississippi River bluff country, let me know, place is for sale). Car runs great, we're at 7200 feet up the Sacramento Mountains and have a few questions on things that need a 'fixin'. It's 1400 miles back and forth, and the fuel mileage was why we bought the car. Our rust-free 1985 Jeep Grand Wagoneer was great for our dogs, but a bit 'spensive to run~!

First, and most important, the heat works only at idle. After searching, I find that the monovalve diaphram is the likely culprit. I've already tried the disconnection of the two-wire plug, no difference. The CCU 'seems' to be working, I can hear the air flow change from upper to lower when I turn the temp thingy, and all the pushbuttons work. So, on the right track?

Also, the car is hard starting when cold outside. I've plugged it in, and, presto, starts right up. However, in milder temps, say, 35 over night, and 50 during the day, it still starts hard cold. I can get it to start, but fuel over-loading creates quite the cloud! Does the car have to be plugged in even in the 35-40 degree overnight temps, have no choice? The ALDA have been disconnected, as well as the EGR.

The sunroof doesn't work, nor do the rear windows, but I have the plastic sliders on order, motors work. Here's a pic!
http://i253.photobucket.com/albums/h...d300SDL005.jpg

Yep.
Sounds like glowplugs.

Second the glow plugs for sure...

I have a 617 W126 300SD and on the drivers front fender well is a box with the wires from the glow plugs, I believe the same is true for your car. My brother had the same car as you different color. If you pull the top off the black box you will see that there is a multi pined connector with the wires going back to the glow plugs. If you pull the plug you can test the viablilty of the glow plugs using a volt ohm meter, either analog or digital to see how many ohms resistence each glow plug drawing. A new glow plug draws approximately 0.7 ohms (Bosch French GP's) new. In circuit you may have a different reading but it will tell you how many GP's are still working and how many are not working. The most definitive way to test a GP is to remove it and with heavy jumper cables carefully connect the Black wire to the silver body of the GP and the Red wire to the threaded end and watch the tip of the GP get red hot within a few seconds. Best of luck with the new car, this site has a wealth of information for you to learn.

Hey all, thanks for the replies. The PO just informed me that he replaced all of the GPs last december. So, I'll check the fender well plug with my ohm meter just in case. dave

Is the glow plug light working correctly? Check for voltage to the plugs also when the key is in the glow position.

I just today, fixed the non-operating speedo/odo with a gauge cluster bought on ebay. Combined the speedo that worked with a side-gear from the spare cluster for the odo. Now have odo and accurate speedo!

However, the glow plug light was not working when I bought the car, we just listened for the buzz to stop before we started the car. I noticed today with the cluster out, that the light bulb for the glow plug relay was missing. My guess it's attached to the one of the other light 'holes'. Will have to pull gauge cluster once again, and turn key on to see which is the correct light. thanks.

Oh, yeah, what does 'corking' mean?

Should be 'working'.

If you have not played with MB diesels before, you will find that not all Glow Plugs are good. What you want in your car are Bosch German or French made GP's other manufacturers GP's just do not hold up.

could be a GP relay fuse too.
get the cover off, and get the meter on each screw and hit the key. you should show 0 volts. if you read ANY voltage across the screws, the fuse is bad.

Or it could be simply not waiting long enough. The buzz has nothing to do with how long you wait for the glowplugs.

yes, what aaa is saying is the buzz is just a seatbelt warning. the GP's stay on for up to 3 minutes, depending on the model controller.
1. buckle seat belt.
2. turn on key, and listen for the CLICK from the controller.
3. when the click repeats, the plugs have turned off. you can tell by the dome light brightening.
4. start the car, if it starts fast, you've found the issue you've been having.

A plug-in digital voltmeter in the cigar lighter can give you a good indication if they're working or not - a healthy set of GP's on a 603 will yank the battery down to 11 volts or below on a cold morning. I don't try cranking over my present 87 300D until the GP's heat up enough that the battery voltage recovers up to around 11.5 volts.

If you know of a controller that runs the plugs for three minutes before start, please furnish the part number.

I'll second the GP fuse itself. Mine looked good, tested bad.. I was able to use a "modern" fuse from the local parts store to replace, works like a charm now.