Before using anything open flame I would use my 1) old electric blanket stuffed under the hood 2) old heating pad (really works good) or 3) the partially worthless magnetic oil pan heater....or a combination of all three given that I had enough extension cords on hand.

This is as bad as the old lady in a Chicago area flea market who wrapped herself and a kerosun heater in a blanket while she sat at the market. It didn't take long before she was on fire.

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Steve A
92 W140 OM603
97 VW Jetta TDI
90 Passat variant TDI 6 speed MT
94 Chevy K1500 6.5TD
05 E320 CDI
+ others