I installed a 1500 watt Zero-Start between the block drain and the head. I bought a Intermatic 40 amp single pole 110vac timer on eBay for 20 bucks. I have the timer set for 1.25 hours before I go out to the car in the am.

That with the 80 watt battery heater (leave on all night) has the 23 year old diesel starting at below -5f with no problem, and lots of heat when I start it up too.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport