300SD cold start.
 

Has been down in the 30's here last couple of nights. I had the block heater plugged in and it seems to be working. However, 2x I had the same problem happen.

Starter will crank quickly like it should but after about 3 seconds of cranking the starter will disengage flywheel. I can hear the starter spinning freely at this point. I can cycle the key second time and starter will engage fine and car will start. It has never happened in warmer weather.

Wiring? Starter on its way out?

Try cleaning your conections first.Battery and starter.Being cold is hard on everything,but if you feel its starter after you clean it replace.I ensure everything is good to go before winter,working in the cold is not fun.

I will have to double check connections. Starter was rebuilt just a few years ago. Battery is not even a year old.

Sounds like the bendix gear on the starter is going. I think this type of symptom is indicative of worn teeth or a broken tooth on the flywheel. First thing I'd check is the starter. Engaging and spinning quickly would indicate the connections are good, especially if the starter engages properly and the engine starts on second attempt.

A good running 617 should never have to be plugged in in Johnstown. My '83 300D doesn't even have a block heater. If the engine is in good shape, the valves are adjusted, all the GP's are working, and you can use synthetic oil, that car will start in any weather.

Last winter, just to test it, as the car is garaged, I left it outside one winter night when the temperature the next morning was 8 deg.F. Without even touching the throttle, the engine starts in about two revolutions- with a six year old battery.

OK. I give. My car is a POS.

May be as simple as the lubricant is hard and the gear does not extend far enough out the first time in the cold. Typical of bendix type failures as mentioned.

AS Barry says, the lube is cold.

Not on a MB, but on our 85 Mazda 626 we had before buying the first MB.

I replaced the original starter with one from the JY. It sometimes wouldn`t fully engage, and kick out. so I removed it, gave it a shot of WD-40, and it worked fine for the next few yrs until we sold it.


Charlie

Gosh, I miss out on so many good troubleshooting / diagnosis opportunities living in So Cal. I miss Michigan sooooooo much this time of year. :cool:

I'm going through the EXACT same thing on my 240D. On a cold start, the starter cranks the engine a few revolutions, and then disengages. The starter free wheels until I get off the switch, and then grinds to a halt. I let it sit a second, try again, etc.

I'm up to 5 and 6 attempts before it starts on most attempts.

My first thought was that it was, as previously stated, cold grease not allowing it to fully engage the first time. But then I got to thinking... wait a minute... it's engaging the very first time. It only kicks out after it's already engaged the first time.

I'd like you to do an experiment to see if your results match mine, if you are willing. Go out one cold morning, and turn the key to start -- WITHOUT any pre heating. No heater, no glow plugs, no nothing. Just flip the key straight to start -- and hold it there until whichever of these comes first: 1) You crank for 10 seconds and the engine doesn't even pretend to start, 2) The engine starts, or 3) The starter disengages as per your original post.

IF your car is like mine --- when you do it this way, the starter will stay engaged perfectly until the engine starts or at least tries to start.

Here's my (and my dad's) current theory. We think that as the engines get older, and the temperatures get colder, we all know it's a little harder to get them to fire. Our speculation is that the engine is "running away from the starter" -- or false starting. here's the scenario: It's a really cold day. The engine is 30 years old, and some cylinders are stronger than others. So you do a nice long pre-glow to be sure it's ready to start, and hit the starter. The starter engages, the engine starts to rotate. One or two cylinders out of the four (my case) or five (yours) -- fire the first or second time around, because they are the strongest. The engine STARTS to catch. For a very brief moment, the engine reaches the speed at which the starter "kicks out" -- and so it does kick out. BUT -- it's such a frigid day that the other 3 cylinders didn't light up, and so the engine dies instantly.

Or the short version: On a cold day, some cylinders fire instantly while attempting to crank it, and so the starter disengages or "kicks out" just like it's supposed to, but then due to the cold, the other cylinders weren't able to sustain the engine so it dies instantly while the starter is still winding down.

I'd be interested to see if you are able to get the same result --- when you start without waiting on a pre-glow, ALL the cylinders have a hard time lighting up, and so the starter goes a full 5 or 10 seconds (depending on your start ability) before disengaging -- if the engine isn't even attempting to fire, there's nothing to make the starter kick out, so it doesn't.

If you don't want to or can't afford to perform the test, then it's fine. But I'm very interested in the result if you do since I've got the same thing and I'm ignoring it for the moment. I considered the "Cold grease" theory but then it just didn't make sense why it would engage the first time and then pop back out, if the grease was preventing it from extending far enough in the first place.

You have a very impressive automobile.

I plugged the block heater in last night. I will leave it unplugged tonight and try tomorrow morning. It will be in the 30's again tomorrow night.

To more easily satisfy your curiosity and remove many variables. Do the glow plug warmup and crank with someone holding the fuel shutoff down. This way you will be almost absolutly certain if what you suspect is true.