Engine barely turns over, but battery is good.
 

I posted about this problem a while back when I thought my battery was bad.

Basically, starter barely turns engine over. In fact it acts just like an almost dead battery would in winter.

But engine and glow plugs are good, so it starts after hardly a single revolution.

In my earlier post, I thought starter motor was just sticky, but even although car is driven daily, the problem has started again.

I fully charged the battery. I also checked battery after a stop start run when on several occasions I didn't think car would start and it was still at over 13V. On earlier occasion, I did a load test on the battery and it seemed OK.

It feels like the engine is tight or has excessive compression and hard to turn over. A/C compressor is disconnected, so it isn't that. What else would do that? PS, Vac pump, Alt? No other signs that those items are giving trouble.

Any ideas?

If you think engine is partially seized when hot, try turning it by hand via crankshaft bolt to verify. Could be bad bushing in starter that cause the armature to jam from being off centered.

If your battery is good, you need to verify engine strap is clean and secure, and battery ground cable is clean and secure, if still weak, swap in another starter.

Among other things, worn starter brushes will cause just that problem.

As has already been suggested ...
 

In Boston-ese "StaaarTaaaaaH"!

Assuming we's talking about the '85 300D

1.How Many Umpity-Zump Gazillion Km on that Particular Starter since a
Major Maintenance?
I.E. Bushings,Brushes,Etc. ?
Lotsa Times Just Blowing out all the Carbonized Brush Materiel Will aid
Performance.If you're gonna "Go Into" the Casing "Do It All".

Access to a D.C. Amp Meter ("Draw") will tell you the Direct Health of the
Starter.

Down Heah, some auto parts stores have available FREE diagnosis Black Box
curbside service (Advance has a particularly Great "One Box Does All" service
That they'll happily hook up to your under hood system and it'll tell all the
Good + Bad!

If the chassis to ground strap is clean, battery cables are free of bulging from corrosion....then you may have to face the music and replace your starter...a bad starter and kill a good battery....

It was replaced in about 1996 at about 210k km. Probably done same mileage since then. Maybe it is time ;) I wouldn't mind putting a new one in regardless, but I seem to recall it wasn't a job I would want to tackle myself. Something in the way?

I have an el cheapo battery/starter/alternator tester. But need to get wife off golf course to help me again. (She would rather I was trying to fix the washing machine which won't run!) Last time engine started so quickly, I never got a good reading. Need to tie down the stop lever as someone suggested in earlier thread and retest. I have a quite good battery out of my E320, that I might try jumpering over just to be sure it is not a battery load problem.

Cables and ground are good at least at top end.

My first thought was "bad starter". 210k miles is a plenty long service life.

However, it is also possible that one of the accessory belt-driven devices is bad, and that is slowing the engine during the start cycle. You would need to loosen the belt(s) to test that theory.

"Weakest link"

- load test battery, you could have a marginally bad cell. Not bad enough to prevent normal operation or even glowing but when hit with the massive current from the starter it breaks down.
- verify the entire electrical path for secure connections - battery + to starter solenoid to starter motor, and block ground to frame (underneath drivers feet) and frame to battery -

Once this is proven then start on the mechanical causes.

My starter on mine behaved exactly like this, acted like a bad battery, even to the point where a jump start would help it crank fast enough to start. Battery tested fine, well in excess of factory spec, voltage was good and stayed good while cranking. Starter tested good at the auto parts house. Replaced starter and all has been well since, great cranking.

I have done the battery load test several times. It seems OK. Not 100% but still withing green on tester. Just have to do the starter load test again.

Funnily enough, today the engine spun and started normally. That's what happened when problem first cropped up a few weeks ago - problem just went away. Hard to trouble shoot! But it does point to some sort of intermittent problem. Could be connections or starter. Just have to keep at it!

As was already suggested it is most likely the starter. It is a pretty miserable job to change on the OM617.

I have had a slow starter before on a ford 2.8 v6 and the cause was it had rusted up inside and therefore did not give out much cranking speed.Ten minutes with a wire brush and it was as good as new.
It was not as bad as the one below in the link but did have at least 60% build up of rust .
https://www.google.co.uk/search?q=rusty+starter+motor+internals+image&tbm=isch&tbo=u&source=univ&sa=X&ei=c4GtU9f2N7DQ7Ab8voGA Ag&ved=0CEQQ7Ak&biw=320&bih=460&dpr=2#facrc=_&imgrc=hUX0Fs8G3jJhZM%253A%3BIAb1hfCJI60HpM%3Bhttp%253A %252F%252Fbluewatermarinesvc.com%252Fimages%252Fgm5.JPG%3Bhttp%253A%252F%252Fbluewatermarinesvc.com% 252Fhtml%252Fgm_starter.html%3B500%3B372

Yes the starter is in a bad spot on most of these engines.

I was trying to help the OP eliminate the possible electrical causes before having to tackle replacing the starter.

Yes, and I do appreciate the idea of doing the easy things first. It might still be a connection problem given the on again, off again nature of the problem. But I am going to check if our local rebuilder has starters in stock.