What will happen if someone hits your low mile expensive w123 or w126? Will the insurance cover it? I'm afraid not.

I think fuel economy between a 320 cdi and 320 petrol is not that big and the 320 petrol might be had for a cheaper price to cover the lost economy.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.