1985 300D Difficulty Starting (COLD Weather)
 

I have 341,000 on my 85 300D. It got to about 28 F here for the past 2 mornings. I almost could not get the car started and am afraid of low compression. I have listed below what I did/have done. Another important question is should I be expected to use the block heater when the temperature gets this cold and this many miles on a turbodiesel engine?

1. Valves adjusted 8,000 miles ago.
2. New battery 2 weeks ago
3. Pre-glow through 3 cycles (until the relay clicks off before trying to start).
4. Hold the accelerator completely to the floorboard while cranking.

Any suggestions greatly appreciated!

Richard

Have you actually checked the glow plugs to see if they are all working?

It probably would not hurt to use the block heater at temperatures. I have not plugged my 91 300D in, it started this morning at 8F without incident.

Its entirely likely that you have one or more glow plugs dead/not working.

Have you tried cranking without touching the pedal? I know it's contrary to the procedure in the manual, but I find my car starts at low temps better if I leave the pedal alone, at least until it starts running--then it helps to up the RPMs just slightly until it smoothes out.

But JamesDean is right about the glow plugs. I put a new set of Bosch Duraterms in this past fall and the difference is huge.
Mercedes Diesel Glow Plug Repair

I live in Canada, and often have to start car in much lower temperatures than that.

If car is in a garage, as mine usually is, it will start without block heater at 28F. If outdoors it seems engine gets colder and battery output is lower. then block heater is needed.

Essentials:
- Good compression
- Properly adjusted valves (I once had shop do them and they had them all wrong)
- Properly working glow plugs. May need to ream out pre-chambers
- Good fuel.

If you wait until the relay clicks off, the glow plugs will not be energized when you turn the key to the start position. You should move the key to 'start' before the relay kicks off so that the plugs are on while the engine is turning over.

You don't mention the age of the glow plugs. If you are glowing multiple times and it barely starts, I think you either have weak glow from old GPs, or at least two not working at all. As long as the #1 plug is working, the glow light will show on the dash. That doesn't mean you have adequate heat.

My experience has been that here in cold eastern Canada, valve adjustment issues often show up before the temp you describe. As Graham pointed out, around here 28 F (-2 C) is hardly even a cold day at this time of year. The motor would have to have very low compression figures to refuse to start at that temp. (I know -- I drove a high-miler 300sd with a pooched motor through one winter.)

Tonight in my area we are going down to -31 C (-24 F) and the windchill factor will be -42 F.

As mentioned, good glow plugs are a must.

Synthetic oil too.

And a good starter!