I have a 77 300d and an 85 300td. It was 10 below zero this morning. I plugged in the 77 since it had starting problems in cold weather last year before I started using synthetic oil. The 85 was not plugged in.
The 85 started right up as if it was 70 degrees. The 77 did not start even though the temperature gauge showed the block heater was working. The difference was obvious and I knew the 77 would not start the minute my wife turned the key. The starter simply was not spinning the engine fast enough whereas on the 85 the engine was spinning at its usual starting speed.

Why the difference? I have a new battery in the 77 so I don't think the difference can be attributed to old versus new batteries. Could the difference be in how the alternators are charging the batteries or could the difference be in the starters themselves? Even in warm weather, the 77 does not spin as fast when starting as the 85. Were there different kinds of starters installed on these engines?
It may not be worth trying to solve the problem because we only rarely get temperatures this cold in Denver and the 77 has started regularly without being plugged in at temperatures down to about 5 degrees. However I would like to be able to understand the differences in these starting characteristics. (I know each has different style glow plugs but I don't think this is relevant to the speed at which the engine turns)

Anyone have similar experiences or good hypotheses?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I have noticed that the starter in my 1979 300CD isn't always spinning very fast also. I have noticed sometimes that it will spin faster than other times when it is cold. I have however found that when I plug in my battery heater the starter spins much faster. I need to remember to plug it in more often.

There are several things that could explain this. To begin with the '85 is a pin type glow plug engine, while the '77 is serial. Even so, if everything is right, the serial system should glow well enough to start the car.

On the '77 check voltage to the glow plugs. If there is voltage, do a compression test.

Good luck,

I'm pretty sure it's not compression or voltage. The glow plugs are new in both vehicles and seem to be glowing appropriately in all conditions. I'm almost certain it is just the speed at which the engine is turning over. I don't have a tach on the 77 but I would estimate that it is turning over at only half the speed of the 85 or possibly less.
Last year when I had this problem with the 77 I put a charger on the battery and warmed it up. When I did the engine turned over much faster and it started right away. (I've since replaced the battery so I think I can discount battery condition) I'm just puzzled about why two vehicles sitting next to each other in the same conditions have such a big difference in the speed at which the starter turns them. I know I could put a battery heater in the 77 and probably take care of the problem, but I'd like to know why it is happening. Since the engine was acutally warmer in the 77 than in the 85 since the 77 was plugged in, the answer must lie somewhere in the electrical--battery--starter component of the system. I think??

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

You say the 77 was not spinning fast enough right off? On my old well worn 78 I have run into that issue a few times over the years. Don't get nearly that cold around here, but still my car has had some slow starts, or failures to start over the winter seasons.
I did two things to get the old diesel to turn over in the AM better. First was I replaced the short ground cable with a new and very heavy one. Scraped and cleaned the contact areas and then used electrical grease on them. After that and some improvement I finally just replaced the starter with a fresh rebuild and replaced the positive battery wire also. Gave it the same treatment where it seemed appropriate.
Has started fine ever since, except for a couple of battery failures. I blame that on a series of Exide batteries I had in there. Kept replacing them with warrenty batteries and they kept letting me down.

I would look at the quality of connections from the battery to the starter, including ground straps.

I found that after I replaced the dead starter on my '75 300D, years ago, with a used starter from an '80 something 300D, the cranking speed of the motor greatly increased to maybe twice that of the previous starter. It also started MUCH easier.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Another thing it could be is your alternator might be going bad & not charging your battery enough. I just had to replace mine & it made a big difference. The voltage drop wasn't enough to really notice for probably two months before I got the low battery light. Might just be changing the voltage regulator, maybe the whole thing. If you have the Bosch regulator you can remove it easily with two screws & check the brushes. It they're worn down it'd be worth the $20 to replace it & see if that fixes it.
Good Luck!

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Michael Roth

1982 300TDT Wagon
1982 240D Euro!, 4spd manual-Parts car now, dead engine
88 Jeep Grand Wagoneer-fixing up for offroading
1989 Ford F150 (rust bucket) For Sale!
1953 Dodge B-4F, 1 1/2 ton Stake Bed (new restoration project)

I agree with everything posted above and think you should check everything suggested that you have not already taken care of.

That said, I think it's the starter. I just replaced mine and my '81 300CD has never started so well since I've owned it. I kept blaming batteries, compression, etc. , but it was a nearly worn out starter. The car would start relatively quickly most of the time, except at below zero. It would start then, but it took a little more coaxing. Now the car starts almost immediately at all temps. I love that.