-10 here in NH - can't get the 1979 300D to start
 

So I threw an alternator belt 2 weeks ago, overheated.
Got that squared away - and now of course the temp drops to the lowest its been in 2 years - and I can't seem to get her started.

I have an oil pan pad heater, a battery pad heater and a lower radiator hose heater. Had all 3 running last night, went out to start this morning and could not get it to turn over.

I glowed 2 cycles, I depressed the pedal one time fully - then about 1/8 down during the start. I held the ignition in starting position for over 30 seconds, and could not get it to turn over. Tried again in a few minutes, prob held ingition in start position for almost a minute - I heard a few good stutters like it was about to kick over but did not.

The last 12 months I have had rough start issues, after it does turn over I get a bad shutter, stutter like all cylinders are not firing - I know I need new injectors, and always attributed this to poor fuel flow, since it went away after it warmed up

How do I know if my starter is not strong enough to do the job?
Could the old, knocking injectors just make it even more difficult to start?
I have replaced the glow plugs once, moving to the new style injectors (did not replace the gp relay).

Thoughts, suggestions?

When you stay 'does not turn over' do you mean the engine does not fire or the starter does not turn the engine? It could easily be that your battery is weak and not turning the engine fast enough. Do you have synthetic oil? Thick oil can be a serious impediment to an engine turning fast enough to start at those temperatures.
Also a little unclear on the glowplugs. When you say you went to new style injectors, do you mean you switched to pencil style plugs as opposed to loop style plugs?

Engine does not fire, the starter is working hard and trying to turn it over. The battery is 4 years old, 900CCA. Do not have synthetic oil...should I drain and put in some 5W/40 Rotella? Did not change injectors, assume they are original (I know they need to be replaced, have been knocking for a while). Did go from the coil style glowplugs, to whatever the kit dieselgiant sells, (cant remember if its pencil or loop sorry).

Synthetic oil would get you a faster cranking speed which might get it going.

IF -- big big if -- your glow system is in good shape -- then I suspect you've got the same problem my 240D has... just worn out. Low compression from engine wear = cold starting becomes harder and harder.

I've got a PERFECT glow system on mine and it STILL won't start at 15 degrees or colder without external heat. The only remaining possible explanation is low compression. It also burns oil like a burning well and has huge amounts of blow by so it makes sense.

If yours is equally worn out then it's probably just not going to go. If it's low miles, low wear -- then keep checking glow and voltage systems.

How many miles on the engine? Is the glow plug light working? Have you checked for voltage at the glowplugs and ohmed them out?

237K miles, I drive it everyday - not sure how to gauge engine wear. Ive never done a compression test. I also burn oil, and have blow by.

237K miles, GP light works fine.
Have not ohm tested GP's.
My voltage meter is like japanese to me...all symbols...what would I set it to to test? Put neg to neg term on batt and touch pos to each gp?

The ohm's symbol looks like a horsehoe kind of. Put it there at 20 ohms and put one one on the glowplug and one end on a ground on the engine. Each plug should show less than 1 ohm's resistance or thereabouts.

in order to test with an ohm meter, you will have to remove the wires from the plugs.
the DG upgrade kit uses ONE wire for all the plugs. this makes it difficult.
another test you can do is turn on the glows, wait about 30 seconds, then put your finger on the end of the wire and see if it's getting hot or not. if you have a amp meter, you can measure amperage, but since you are having difficulty with the symbols of the standard meter, it's unlikely... if you cannot tell if the plugs are working, the next step is to pull them back out, and power each one individually, and verify it gets bright orange/yellow quickly. any that don't, need replacement.
let us

Heat. My 240D needs a valve adjust, maybe just some anti gel- won't cold start when soaked to low teens like it used to. The 2 previous winters I drove it a hairdryer under the hood for a couple hours and blowing on the block would do it. About 1/2 hour with a torpedo heater pointed at the car will get you a toasty block and heat on startup- be sure not to melt the bumper rub strip.

Another useful thing is bring the battery inside overnight. Cranking amps and life are much better when it's warm.

Are you glowing for a full cycle and cycling the key to start on the second?

When checking ohms its always a good idea to short the probes which should result in a 0 (zero) reading. If it comes up reading .3 ohms or something at least you have a known to deal with for your GP reading.

Doing that on any scale but ohms does nothing.

VSTECH - the DG kit contained multiple wires, each connecting to the next GP. So since they are all connected, the ohm test will not work? Based on all of the above, you would blame possible bad GP's, not weak starter?
I'll still make the switch to synthetic oil, and will try my best to test gp's.

How do I power each individually if I can take them out?

In addition to all of the other good things you are doing, try putting a trickle charger on the engine overnight. That not only makes sure the battery is fully charged but helps keep it warm -- and from the inside out, which is the best way to warm something.

I tried something different this year, fuel wise.
10 gallons diesel, 1 gallon kerosene, 3 oz Power Service & 1/2 bottle diesel 'dry gas'
10 - 15 below last night. Cranked 15 - 20 seconds but it did start

When was your last valve adjustment? When trying to start under extreme conditions it is imperative that your engine be creating as much compression as possible. If the valves aren't adjusted properly it will create hard starting in cold weather even if the GPs and everything else is OK.

I'd also highly recommend using some power service (white bottle) to prevent gelling. Even winter blend fuels will congeal under below zero temps. I would bet your problem could very well have been gelled fuel, especially on a car that isn't garaged and gets full exposure to the elements.