How long safely crank starter?
 

Glow plug issues...need to get them replaced. In the meantime: for how long can I safely crank the starter before giving it a rest? How long between attempts? 92 300D.

It depends, really. I have perhaps a bad glow plug or two, the engine speeds up drastically, so I continue cranking and sometimes I just rest my foot on the pedal. on the coldest day I've had to crank a lot longer than normal, but the starter was just fine. No ill effects at all.

Crank for 30 seconds and then let it cool for a minute or so between crankings.

Replace the GP`s to save the starter. GP`s are a lot easier and cheaper to replace than having to replace the starter. No ill effects now, but old man winter is just around the corner.

Charlie

I tested the plugs a couple of days ago.....three bad. Maybe more by now. With some effort, it started tonight at about 45F ambient.

For me it depends on conditions.

When trying to re-prime the fuel system on my 300SDL which lacks a hand pump as do all 603's, I follow the owners manual. 60 seconds at a time, cool for quite a long time between attempts. Usually doesn't take that long but I've run it about 50 seconds before and it survived.

When cold-starting, I listen very carefully to the engine turning over. This is particular true for my 616/617, both of which are terribly difficult to cold start compared to my 603, which starts immediately after one glow cycle at 0 degrees F.

In those conditions, I listen to the engine. If it's only turning over at starter speed, not even one cylinder "trying" to fire... I only run it 10-15 seconds and then I do two or three more full glow cycles (1-3 minutes total) and then crank some more. More than that and I figure it's not making much heat anyway.

On the other hand, if I hear one, two, or three cylinders "starting" to fire and helping out, I will crank for as much as 60 seconds in an attempt. My logic is that if the thing is even carrying half the load itself, once the engine starts to "run away from" the starter, the load ON the starter slackens. In addition, I figure that the heat thrown into the engine by those firing cylinders is doing me some good in getting the engine running, moreso than the glowplugs which have already, at this point, failed to start it on their own. (Even when they all work.)

If I hit 60 seconds and I've got four out of five and it's just "almost" running, I'll keep holding it until it starts or until it slows down and I lose momentum, at which point I stop and re-glow.

I agree that new GP's are cheaper and easier than new starters, but if it's cold enough, I've got a few (especially 61x engines) that just plain won't cold-start nicely even with brand new glowplugs, brand new battery, and good electrical connections. Can't make up for compression loss and extreme cold, and on those I'll take some heat any way I can get it whether it's glowplugs or cranking effort.

On the 617 engine, MB recommends to keep the starter engaged if only firing on a few cylinders until all the cylinders kick in.

While you're at it, trickle charge the battery overnight so it's warm and fully charged, then put a full battery charger on while you're cranking. It will help to keep the starter motor running at full speed and thus assist the starting process.

Even if you have only a couple of good glow plugs, do a full 30-second pre-glow. Having a couple of cylinders firing is better than none and helps convince the others to start.

Jeremy

They say your best chance at starting is the first crank... after a good healthy dose of glow. (Assuming you've got fuel flow). Foot to the floor, glow 20 seconds, turn and hold until she lights up and continues on its own. All well and good to say that! My nerves last about 60 seconds before I think it's going to fry the starter... then I move onto crank #2.. and #3 and battery is producing less torque, less compressions, less oomph to glow as hot... etc.. But one way or another I've always gotten her going. Re-priming the 603 is the worst... using the starter motor to do that, when a bulb would be preferred and easier on the battery etc.

Anybody put a manual primer on the 603?

I put 5 wt oil in my 81 300SD in the winter and it helps a lot. We have not much cold weather in Atlanta but in the 30's degree weather, it will start pretty well with the thinner oil.