96 300d... how cold is too cold?

[landev]

Welp... after much ado getting new glow plugs installed in my 96 E300D, I figured it was ready for anything. Drove it to work yesterday... started just fine (block heater plugged in), then when my wife went to use the car at lunch, she had a heck of a time starting it (temp in the mid teens) and got a battery charge warning. She finally got it started, drove it a few miles, then parked it at work again. When 4 pm rolled around, the car started just fine.

Today, we went into town (started just fine again) and the car sat until 4 pm again. I was the one to try to start it this time... NO GO! Cranked--rested--cranked--rested for several minutes... got the battery charge light, so flagged down a jump start (mid teens again BTW.) After several attempts, the beast finally started. Not good for the battery, I suspect!!!

I was worried that I had a frozen fuel line or something, but once it started, it ran just fine.

'leads to the BIG QUESTION: How cold is too cold to drive this car if it's not plugged in? It seemed to do fine when the temp was above 30F... but getting stranded when it weather is in the mid teens is not my idea of a good time.

At what temp should I consider driving a gas burner?

Thanks in advance!

-l-