300SDL Cold Start Roughness and Smoking - PeachParts Mercedes-Benz Forum

Lance Allison · #1 04-08-2003, 08:37 PM

My 280k mile 87 300SDL has developed a problem over time that I think needs to be addressed sometime soon. First of all, I should mention the obvious things were checked. New air filter,fuel filters, tank sock, 25k miles on injectors, glow plugs are relatively recent and have tested with a meter to have proper resistance. I use Delvac1 5w40 synthetic oil. Also, the car has about 40k on a new head and valves and 90k on the turbo. Compression is fine across all 6 with almost no deviation. Coolant is clear and I don't have any issues with overheating. Oh yeah, the timing chain is also about 90k old. (The turbo, trapox, and timing chain were replaced at 190k).

Ok, now with that said...here's the issue. When started from stone cold and the air temp is below 40-45 degrees, it runs sort of rough for 15-30 seconds and a good amount of blue/gray smoke is emitted from the exhaust. Even if I turn the key right after the glow light goes out, it catches in a less than a second. Always. The problem improves if I give it 2 full glow cycles, letting the relay kick off between the 2 glows. It will run rough for maybe 5-10 seconds at that point. The smoking continues unless I drive the car for a few minutes. Until I actually drive the car, it will smoke less as it warms up, but doesn't visibly go away. As soon as I drive it just a little bit, the smoke disappears completely (even at idle) and doesn't happen again until it cools down for several hours.

While driving, the car performs flawlessly and returns 26-28mpg at 70mph. The smoke level, even with a heavy foot is nill, even less than my much more advanced VW TDI. The car is very quiet once warm.

Thanks in advance.

#2 04-08-2003, 08:45 PM

I have the same problem at the same temperatures. It used to start right up from 220k miles to 250k miles.. then the next winter i had the problem at like 280k miles or so. I have good injectors (old, but no symptoms or problems), timing chain 40k old and new fuel filters.

I took it to my mechanic and he said it's a common problem with these early 603 engines, it's not the engine but the injection pump. The lobes or valves inside get worn and it acts up in cold weather. He tells me the only solution is a rebuilt IP.. i'm going to live with the problem.

From 40-50F or below, my car starts instantly with 1 glow plug cycle but idles rough, puts out blue/grey smoke and revvs very slowly. It clears up in a couple revv's, and all is well until the engine is dead cold again.

janko · #3 04-09-2003, 09:04 AM

i have similiar condition with my 86 300sdl. although my mileage is a little less at 185k. was thinking prior to this, that i should replace the glow plugs. perhaps i will live with the rough idle when cold for a little longer.

Tom Sweeney · #4 04-09-2003, 09:04 AM

Mine does the same thing. I did notice this past winter that when I plugged in the block heater the symptom disappeared, it started normally. My block heater is on a timer and only runs for 3 hours, set to go off when I leave for work. Have you experienced the same results using the block heater?
Tom
'82 SD
'86 SDL

surfblau · #5 04-09-2003, 04:27 PM

It only happens below 40 degrees (only when I go to SLC in winter).

It never happens in san francisco.

I have no other problems, so I am living with it.

alec

Wallknight · #6 04-09-2003, 08:24 PM

Same here.
I noticed it got worse after a recent valve clearance job. But the car runs better when warm, and I went and double checked the clearances. My current theory is that the valves have turned a slight bit and need to reseat on the crud. So, my next step is a can of diesel purge. I'll let you know when I get around to it.

ps. Just dumped in some Bardahl stop smoke. Seems to have a bit more power now.

psfred · #7 04-09-2003, 09:09 PM

Run a bottle of redline through the next tank, should help.

Do you do lots of low speed traffic driving? If so, an Italian Tuneup will help more than anything, our diesel NEED to be run hard once in a while to keep the nozzles from sooting up.

My 300D was doing exactly what you described -- rough idle on startup cold, more whitish smoke than I like, and a distinct lack of power cold, goes away as soon as the turbo comes up.

I blew an injection line a couple weeks ago, and since I replaced it (#4, the "problem" cylinder), I no longer have more than one or two "thumps" on startup and don't have the low power problem nearly so bad. It's also warmer, though.....

Peter

Lance Allison · #8 04-09-2003, 10:12 PM

Actually, my drive to the office is 60 miles each way, all highway and since I hit the road at just before 5am, there is no traffic. I'd be amazed if I saw 3 cars the entire trip. I'm certainly no light foot either.

My commute is like this...I pull out of the garage, drive 2 blocks to the highway. Continue for about 6 miles and connect with another highway. Take this highway 50 miles south and drive like mad. Finally, proceed on a suburban-type 2-lane highway for about 4 miles to my office. Turn into the complex, drive about 1/2 mile, go up to the 3rd level of the parking deck and back into the first spot that has a walkway on one side and a support beam on the other. No chance for door dings.

Oh yeah, I can do my morning commute (house door to office desk) in 45 minutes if I try hard.

Thanks again.

Ken300D · #9 04-09-2003, 10:48 PM

My 1987 300D does exactly the same thing.

I think it freaked out the previous owner, who owned it from about April to November - no doubt in the colder November weather it started smoking on cold startup. He was not that familiar with diesels and probably thought the engine was about to blow. Got a great deal on the car.

At one point he took it into the dealer for another issue and apparently mentioned the problem. On their service ticket they listed several potential causes: Cracked engine head, bad injector. If he asked about the price to fix a cracked head it may have been the moment he decided to sell!

Thankfully the car runs great within a minute of driving on the road.

One thing I did in an attempt to fix the issue was change all the glow plugs. Certainly a worthwhile task at 300+ miles on the car, and I got a chance to clean out all the accumulated gunk in the intake manifold - the result of the EGR system porting exhaust soot into the intake manifold while the oily steam from crankcase blowby also gets ported there.

With the new glow plugs the car starts instantly and smoothly. You can tell though that as the glow plugs cool down in a few seconds, that's when the rough running starts. Later Mercedes diesels modified their glow plug systems to keep the glow plugs hot after the car starts for a period of time (up to a minute or so, depending on ambient temperature). That seems to help the issue.

Ken300D