@D.O.G. - I was thinking the same, about using some bicycle parts. Actually I tried making an automatic system - I bought a thermostat which I would use to open the grill block. Unfortunately the thermostat that I bought I meant for 89 degrees C and my coolant has a temp of about 82.
And the summer wouldn't be a problem since the grill block would close only when the engine is stopped.
@Nicky I can't use a block heater, I don't live in a house - I live in a flat, and the parking space is about 100 m away. Also, I don't really like the idea of a block heater - is like cheating
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After the tune-up I did a refill and the FE for urban driving is about 7.8 l / 100km - that is about 30 mpg. Which is pretty good - it's above the factory rating.