Cold start problem 300D
 

My 85 300D Turbo is having difficulty starting on cold mornings (below 35f).

the glow plugs are good, and the battery is strong (luckily).....Oh and it has 570,000 miles on it......I have only owned it for a couple months.

looking for where to go now...


thanks to all................

Hello,
What weight oil are you using, and how fast is your idle set? I put a new set of glow plugs and some 5W-30 Mobil 1 in my car in January, and it made a world of difference. I just started my car (after 2 glow cycles and 10 seconds of cranking) at -8F. Any idea of how good the general health of the engine is? Poor compression can make for a hard start too.

Good luck,
Nate

How long
 

How long has it been since the valves were adjusted?

Im using 10w-30 oil, and the idle is set pretty low (around 6-7000 RPMS)....

Iwas hoping no one was going to mention it could be a valve adjustment need, that is where I was leaning...One I do get it going, it runs pretty rough for a while.

"jed Im using 10w-30 oil, "

You should be using a diesel rated oil, such as Delo 400, 15/40 and a valve adjustment would be next on my "too do" list. with 500K+ the compression might be a tad on the low side

Once it gets going it's rough running? Are you sure the Glo Plugs are working? They need to be tested individually by removing the plug in harness at the GP relay and test each to ground. Depending on the meter or cont test you do, they should show somewhere just over 1 ohm or with a continuity test they will show shorted out.
If that's not it, diesels need good compression to start in the cold, the valve adjust is next.

I think you mean 6-700 rpms, not 6-7000 rpms, anyway, you should turn up your idle to around 800 rpms, and do a valve adjustment.

Springs coming. Even to the mid West! Just got back from Chicago where it was snowing yesterday. If you can tough it out a couple a three weeks you won't have to worry about it until next fall....

So, glow plugs are good, but...
 

Are all the glow plug wires and connections sound? Dougmcp's suggested method of testing the GP's will tell you. That's the method suggested by the factory service manual.

Do the glow plugs have power? You should have 12 volts between the relay output pug connections and ground.

If not, check for continuity across the strip fuse on the relay.

Cold Start List
 

First glow plugs; I check plugs with an amp meter plugged between the battery and each GP socket on the relay output connector. Replace the 80 amp fuse. They often develop a hairline crack which you can't see till you take it out.

Valves are the next most likely culpret. Set them COLD after the car has sat overnight. Use a new valve cover gasket.

While setting valves, I'd check timing chain stretch. If the valves are getting to 4 or more degrees delayed, that can affect cold starts too.

IP timing would be the next issue, but only if it's way (6 degrees) off.

After these, I'd assume low compression and just use a block heater. I live at 6000 feet elevation, so cold starting ability is an issue here. I've been learning and working on (3) 300D's the last 3 years.

Bruce McCreary
(2) '85 300Ds, '83 300CD
Snowflake, AZ

You may want to do a little background work to establish if this is the original engine or a replacement at some point. Or perhaps engine has been rebuilt? Anyways before really starting to spend money would do a compression check and leakdown test after valve adjustments and glow circuit properly check out and if situation is not improved. Then with good or reasonable numbers you may start looking for things like slow starter, weak battery, air in fuel or anyplace you want to look. But if numbers turn out bad or marginal you pretty well have your answer unfortunatly. :) Also would cause no harm to check condition of timing chain and pump timing as perhaps have not been done in a long long while. This of course eliminates possibility that chain is about ready to go as well. Of course you might have the service records on this car and that would be most helpful I would think. One post suggested just using car above it's normal starting temperatures and thats pretty positive as well if engine turns out to be quite weak. Edit: previous post went up when I was compiling mine. Like his ideal of checking each glow plug by current draw and will have to think about it. Problem is to get an ampmeter with large enough range to be practical. War surplus? You can learn to get by with a block heater in a lot of instances but again not in all. I know I have diesel cars that I use in winter months that could have their cold start temperatures lowered with some effort but just get by using the block heaters instead. This also eases the cold starts and helps prolong glow plugs, starter, and other components lifespan. This area is one of the most commonly brought up on mercedesshop site. Probably a lot of helpful suggestions in search format. Always wondered how the german army got these engines to start on the eastern front in russia during the winter. Finally decided they probably never turned them off. Perhaps they were not used on that front but the russian tanks had diesel engines so it was possible to start and run diesels way back then at extremes of low temperatures. The germans appeared to spend the design effort on their gas designs as two of my early post war mercedes gas cars always were capable of starting at extremes of cold when my american cars were not interested. Each required a large capacity battery as they were very poor starters in comparison when block was at operating temperature though. What I really am getting at is that the germans could have designed a better cold start system for these early diesels in my opinion and it's a shame they did not. :(

thanks to all, I check all suggested culprets.....

thanks again