[perl4ever]

>Rough metric is you get 1 hour of engine idle per gallon. Some cars do better than that.

I have a non-plug in hybrid, that gets almost 50 mpg consistently; I've got to experiment and extrapolate to see if it's much better. I would like to believe so.

I recently learned of the existence of:

https://en.wikipedia.org/wiki/Gasoline_heater

and wonder how efficient they are.

These seem to be mostly outdated, but I guess that they are particularly useful with air cooled engines, where a conventional heating system doesn't have coolant to work with.

[caf]

You can buy diesel heaters for caravans, they seem to use about 0.6-0.7 litres/hour (eg. this sort of thing: https://www.amazon.com/dp/B07K1JJ92S/ ).

[bagels]

Can you even idle all hybrids? Doesn't the engine shutoff when stopped? Maybe it will turn on if the coolant temperature drops?

[perl4ever]

That's the point.

Mine does shut off, if the vehicle isn't moving and the interior temperature matches the climate control setting.

So I would think/hope it could use a fraction of the fuel by running intermittently.

[ddingus]

It's gonna be. My normal non / hybrid Honda uses about 1/3 gallon per hour.

[CompuHacker]

A Honda Civic with a D17A1 engine, at idle, with all accessories off, at 700-720RPM, reports 0.6-0.7L/h, or 0.17-0.19 Gal/h over OBD-II. Vent Fan to Full and Mixer to Hot without A/C reports 0.9-1.0L/h, or 0.24-0.26 Gal/h.