1976 240D...need some help!!

[Army-Ant]

Hello...this looks like a great forum. Im new to the MB scene. Ive got alot of questions (some of them probably painfully obvious), but I am not the wrencher that some of you appear to be. So bear with me, please.
(Same old story, new guy) I bought this 76' MB 240D W115 (115.117, D-4, fuel injected, auto trans.) a few days ago. It starts and runs OK...but there are some issues that I could use some help with.

1) It appears that oil leaks from the oil filler cap..not alot but enough that its noticeable...the cap looks aftermarket...it fits a little less than snug. The PCV valve does not appear clogged. What could the culprit be?

2)Can someone explain glow plugs to me in plain layman English?

3)While on the issue of glow plugs, the round thingy on the dash that is supposed to glow before starting...does not. When starting, I wait about 20 seconds before pulling the start knob...but it doesnt always start on the first try....it takes about 4-5 attempts holding the knob out for about 8-10 seconds...before it will turn over. Does this mean my glow plugs are bad or dirty? Should they be replaced? I read somewhere in here that someone cleaned them???

4)On replacing things...what should be done as far as maintenance? Change oil, oil filter, fuel filter (are there 2?), belts...what else?

5)The A/C still works, but makes a loud crunking noise only when idling, it goes away when accelerating...what could this be? Maybe a loose belt...Is the belt thats positioned the highest and farthest left (if looking at the engine from the front) the one attached to the A/C compressor? If so, it has about a 1/4 inch in play...should it be tighter? Could this be my crunking noise?

I'll stop here for now.
2 more questions...thats it, non mechanical...
Is there a place on the web that sells pre-cut carpet for this model Benz? Are the Haynes manuals any good?
Thanks in advance to all those that may reply. Any help is truly appreciated. I hope this is the right place to post my questions and that I can become a regular poster on your forum. Thank you.

Anthony
76' W115 240D

[Mike D]

Let me try to give you some insight on a couple of your questions.

#1. It's called "blow-by". It is actually a mist of very fine particles of unburnt fuel, oil droplets and possibly bits of exhaust gasses. It can be caused by, worn compression rings, worn pistons or cylinder walls, leaking valve guides or a bad cylinder head gasket. Some amount of "blow-by" is normal. It is usually captured by the tube leading to the intake manifold or air cleaner. Since this is a diesel, there usually is only sufficient vacuum present to pull the mist into the intake process above idle.

#2 A "glowplug" is basically like the element in a toaster oven. In a Mercedes, it's easiest to think of it as the filament in a light bulb. When electricity is applied to the light bulb the element glows red/white hot. This "preheats" the chamber and inflowing fuel/air mix. Diesels "fire" on compression. Compression creates heat. The glow plug simply warms up the elemnts involved to expedite the process. Once the engine starts, the cylinder walls and head heat up and the glow plug is no longer needed to ease the process.

[Army-Ant]

Thank you Mike. That is exactly what Im looking for. Straight forward answers. You say some amount of blow-by is normal...if I can find a MB oil cap and it stops the blow-by, is that bad?
Do you have any insight on #3?

Thanks

[Mark DiSilvestro]

Try to get a Mercedes cap or at least a new gasket to make yours fit tighter. Can't speak to #3 as my '80s diesels have the later generation glowplug system without the 'round thingy'.
1/4 inch play doesn't sound excessive for the AC belt. As the diesels have a lot of vibration, check for any play in the AC compressor mounting bolts and brackets. Look for loose or missing bolts, and (if applicable) damaged or disintegrated rubber mounting bushings. Also check for a loose brace from the bottom of the compressor bracket to the left-side motor-mount pad on the engine block. The brace could even be missing as sometimes lazy 'mechanics' don't reinstall it after replacing an alternator or waterpump.
If everything at the compressor mounting checks out OK, the AC belt could be glazed or burnt.

Change oil and filter. Use a diesel-rated oil, such as Shell Rotella 15w40. If you change the fuel filters, you'll need to bleed the diesel injection with the hand primer on the injection pump. Look for details in your 240D owners manual.

The Haynes repair manuals are better than nothing but I find they have too many omissions and inaccuracies for serious DIY wrenching. Try to find some factory 240D repair manuals on craigslist or eBay.

Happy Motoring, Mark

[Army-Ant]

Thanks....Im going to check out what you suggested. Im going to buy the oil and a set of GPs later this afternoon. Theres a guy parting out his MBs....I asked about the oil filler cap...will wait and see.
The owners manual is not detailed enough for me to do the fuel bleeding . Im gonna wait till I get a Haynes manual to do the fuel filters...Im not even sure where the 2nd one is.
Thanks

[Army-Ant]

Hey Mark...just as you mentioned...bushings are worn thin and 2 bolts missing. Of course I dont think this solves my problem...hopefully it will help a little. I really want to replace all 3 belts...any advice??? Where can I pick up bushings?
Thanks

[Mark DiSilvestro]

Strange your owner's manual has nothing about bleeding the diesel. My '82 240D has primary L-shaped plastic fuel filter near the left inner fender, and a main screw-on fuel filter that looks like a small oil filter, at the left front of the engine. The hand pump sticks up out of the injection pump. If you need to bleed the air, unscrew the plastic cap of the plunger and pump it several strokes, then push it down and screw it back in place.

You could have something wrong other than bad glowplugs.
Get a repair manual that covers the W115 cars and check out the system before changing them.

Happy Motoring, Mark

[Mark DiSilvestro]

Originally Posted by Army-Ant

Hey Mark...just as you mentioned...bushings are worn thin and 2 bolts missing. Of course I dont think this solves my problem...hopefully it will help a little. I really want to replace all 3 belts...any advice??? Where can I pick up bushings?
Thanks

Securing the compressor will help alot. For the rubber bushings, try Phil at PartsShop/Fastlane, the parts place that sponsors this Forum, or the Mercedes dealer. Otherwise, you'll need to find something similar (maybe a shock absorber bushing) and improvise.

Happy Motoring, Mark

[Mike D]

#3 1976 was a crossover year. Some of the engines have the old style "loop" plugs and the rest have the newer "pencil" style.

If you do have the older type glowplugs (easily distinguished by both their larger size and the fact they have a large metal "loop" filament connecting each glowplug) then the starting procedure is this:

Turn the key to position #2. The alternator/battery light will glow brightly. Pull out on the start handle to the second position (you will feel a spring resistance). The Alt. light will dim. Hold this position for about 10 seconds. You should get a red glow from the "pepper shaker" (there is an element behind the metal grill). Pull the knob to the starter engaged position and release when the engine catches.

The time spent needing to "glow" will vary according to outside temperature and engine temperature. You'll learn the correct amount.

[4onthetree]

Quick story from another Benz newbie about the glow plugs. As Mike D mentioned, pulling out the handle until the full amount of spring resistance is critical. A month or so ago, I finally found what appears to be a decent '72 220D on Craigslist for a decent price and couldn't get it started after bringing it home. The PO told me he never really saw the pepper-shaker glow, even though it was supposed to, but it usually started up after a couple of tries.

After I got the car home (notice I didn't say "drive" - different story), I couldn't get it started. It wasn't until I realized that the pre-glow position wasn't simply the "on" position until I read about the starting procedure in the owner's manual. It was quite the humbling moment, but did I ever feel relieved when, after going back out to the car and holding the switch in the correct position for about 20 to 25 seconds, I saw the pepper-shaker glowing bright red. Another pull on the switch and the car started in less than a second.

I'm guessing I'll need to replace the glow-plugs before too long, but for right now I've found that simple patience is the key to a good "cold-start".

[Army-Ant]

Thanks for all the advice and tips. Heres an update:
The cars starts. Mike D, I did as you advised. But the "pepper shaker" did not glow...I waited about 40 seconds before pulling out to start. It took about 5 attempts. Each time, though, there was no glow. Could it be that the filament behind the shaker is bad? Or do I need to replace the GPs? Id rather not clean them...if Im gonna remove them I'll just replace them. They are the older type...they are connected with a metal squiggly wire. Mark, Just below the GPs...I see a round plastic knob, could that be the hand pump?
Should I change the oil before I change the GPs or does it not matter? Is there some totem pole of importance in how I should do all these things?
Thanks

[Mike D]

Always change the oil first. Lubrication is the most critical thing for maintaining a diesel. CLEAN fuel is second most important.

Connect a test light to #4 cylinder's glow plug wire terminal. Do the pull action and see if the test light lights. If it does, then the pepper shaker's element is okay (the element acts as a fuse by the way). You MUST have continuity in all 4 glowplugs to complete the circuit.

I'd replace all 4 just on principle.

Pay close attention to the routing of the metal grids. If you get one wrong (usually the one between #3 and #4 behind the injection pump) they will touch the block and short out the system. Go ahead, ask me how I know.

Clean the ground connection (the metal braid or heavy gauge wire leading from #1 to the block) very well. It is as critical connection as the power feed leading to #4. Use a file and wire brush to clean the small loops in the interconnecting grids. Don't bother with any type of protectant grease or sealant such as dielectric grease on the loops. They will just cook it off as they get HOT during the glow process.

Do use antiseize on the glowplug threads themselves. You'll find out why when you take the old ones out. When you take the old ones out, if they bind, spray them with a penetrating oil and tighten them back in a few turns. Back them out, spray and back in. WORK them out, don't force them!

When you have all the plugs out, crank the engine over a few times to blow all the loosened crap out. Now is a good time to do a compression test.

I've only seen one pepper shaker element go bad. That was caused when some fool, ahem, didn't pay attention to the routing of the interconnecting grids.

[diametricalbenz]

Originally Posted by Mike D

#3 1976 was a crossover year. Some of the engines have the old style "loop" plugs and the rest have the newer "pencil" style.

If you do have the older type glowplugs (easily distinguished by both their larger size and the fact they have a large metal "loop" filament connecting each glowplug) then the starting procedure is this:

Turn the key to position #2. The alternator/battery light will glow brightly. Pull out on the start handle to the second position (you will feel a spring resistance). The Alt. light will dim. Hold this position for about 10 seconds. You should get a red glow from the "pepper shaker" (there is an element behind the metal grill). Pull the knob to the starter engaged position and release when the engine catches.

The time spent needing to "glow" will vary according to outside temperature and engine temperature. You'll learn the correct amount.

1978-79 was a crossover year for glowplugs in all MB diesels, at least in the US for W123, W116 cars. All of the W115's have loop style slow glow plugs unless it has been converted to Bosch fast glow kits with the bypass of the salt shaker and or the relay in the W115 300D.

[Army-Ant]

Mike....which GP is #4? (closest to the radiator or firewall) How do I remove the wire filament (squiggly wires that runs from GP to GP)? Do I bend it open?
This may sound obvious, but can I remove 1 GP at a time so I dont cross any wiring order? Another obvious question, oil pan is up near the front?
Thanks

[Mike D]

#1 is at the front of the engine. There is no "firing order". The glowplugs are wired in series. Power is supplied to #4 (firewall) which supplies it to #3, etc..

First, remove the injector lines. You can do it without removing the lines but I don't recommend it for the first time you try. This is a good time to replace the return hoses since they are probably split and rotten at the ends.

To remove the links you need to start at #1 or #4. Remove the small nuts (should be a 10mm wrench but might be an 8mm) on the end of ALL the glowplugs. The nuts might have a flat washer behind them or they might be flanged nuts. The links interlace. Each one receives power and supplies the feed for the next in line. Once you get a close look at them this becomes self explanatory.

Lay the links out in the same order and direction as you remove them. The links have a small loop and a large. There is a large ceramic cup/washer which separates them. Check these for cracks and clean them with hot soapy water and a soft cloth. You might need to soak them overnight. It's not critical these are spotless but you might as well get into the habit.

I believe it's #1 which is easiest to start. Remove the ground strap, ceramic washer, and then the link which sits below the washer on #1 and above the washer on #2. Repeat the process for the rest until you reach #4 which is the same as #1 i.e., the power lead is on the top and the link is on the bottom.