Last weekend, my 1992 300TE 4Matic Wagon, (137,000) was parked outside in Vermont and subjected to a -20 degree night. The next morning, when the weather was a balmy 5 degrees farneheight, the car refused to start. There was plenty of battery crank power, but the engine wouldn't catch. It killed me to keep cranking it that cold, (three tries and I'd let it sit for a few hours before trying again), feeling like I was scrubbing miles off the engine with each crank. When the car wouldn't start after several attempts, I waited until the next day. The second night was as cold as the first - well below zero, and the next day brought the same no start result. Finally, on the third day, with warmer weather, (teens), and a battery jump start from another car, she finally started on the third try.
My car does not have an engine/block/oil/or battery warmer, (another subject I know). It has 10w/40w dino oil and is usually garaged in Connecticut and never subjected to that kind of cold. It also just had a new head gasket installed with new valves, guides and stem seals, as well as a complete tune-up with new plugs, wires, distributor, etc. and has never had a starting problem before this weekend.
This morning though, when I started the car in the garage, (second try), the engine suddenly had a rough idle!? After driving it a while, when it had warmed up, it was still rough, but a bit better. It was the same when I started it this afternoon - rough when cold and still a bit rough when warm. This rough idle is new! Prior to this weekend the car always had a velvety smooth idle and started on the first crank. Now I think I must have damaged the engine by cranking it in the cold without it starting. (Though I REALLY hope I'm wrong.) Are these symptoms related or is it just coincidence? Any suggstions/experience will be welcome. I sure would like to get my old smooth idle and easy start back again. Thanks.

1962 MB 220SEb Fintail Sedan
1992 MB 300TE 4Matic Wagon
1995 Subaru Legacy AWD Wagon

I don't think you caused any damages to the engine by only trying to start it. If you tried to start it several times, there was a lot of unburned raw fuel going into the cylinders. I would have an oil change done as soon as possible.
From you nice warm garage to minus 20, you could have some water condensation in your gas tank, causing some rough engine malfunctions. Get your gas tank as low as possible, pour in a few bottles of gas line antifreeze (methylic alcool) with a good injectors cleaner.
jackD

Thanks, you have put my mind at ease. And your suggestions, both of which I will do, make sense. They are obviously from someone who knows all about cold weather starting, given your locale in the great white north of Montreal, Canada!
May I ask, do you use any kind of battery, block, coolant or oil heater in your MB? I am thinking of installing one in mine after this past weekend, but don't know much about the various types or their pro's and cons.

and the rough idle was not there before, I suspect you killed the OVP or at least the fuse on top of it.
As far as the original problem, since somebody worked on your car recently I would double check all the connections, look for a vacuum leak and check your coil.
Good luck!

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J.H.
'86 300E

I don't use any block heater, oil heater or any other gadget.
The car sleeps in my ''blue sky Moonlit garage'' (i.e: outside) and all I use to start it is my remote starter button.
Temperature went down to - 36 last week for a almost a week and I did not have any start-up problems. it starts in about 2 seconds each time.
What could have happened for your car not starting is probably related to the gasoline you used. In cold weather, the RVP (Reid Vapor Pressure) is adjusted to make gasoline more volatile in very cold weather. if you fueled in Conn, you gasoline was propably not treated for the -20 temperature.
jackD

What is the OVP? I have seen that referenced often in other posts regarding hard starting/rough idle, but it never was defined by those in the know. What does it do? What does it look like? Where is it located in the 103 engine and how do I check to see if it or its fuse was damaged? Thanks.

The OVP (Over Voltage Protector) is located behind a black plastic cover, behind the battery.
it has a red fuse on top. The OVP has been blamed for being responsible for many problems, but is actually a fairly reliable part.
JackD

The OVP-overvoltage protection relay is a box a little smaller than the size of a pack of smokes,and on my car at least,is located behind a panel behind the battery.It's easy to tell which one it is by the blade type fuse on the top of it.

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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight

You might have a marginal ignition coil, or too large a plug gap. Either could cause your problems with the battery loaded by a cold-weather start. Also, a partially sulfated battery may hold a charge well and crank for a long time, but be unable to maintain a sufficient voltage to fire coil and plugs that are in normal condition - while starting. A proper load test will reveal problems there.

Steve