On 13/04/2021 12:45, Paul wrote:
Dave Plowman (News) wrote:
In article ,
Â*Â* R D S wrote:
On 12/04/2021 18:55, Michael Chare wrote:
I have noted that my more energy efficient diesel car takes much
longer to warm up than the previous petrol ones I had.

Don't they?

When I set off driving with the heating set to auto it's about a mile
before there is enough warmth for the car to bother with the blowers.

I've often wondered about that. Surely the answer would be a much smaller
cooling system? Less volume would heat up quicker? But capacities seem
similar to petrol cars. Or could be a diesel efficiency gets much poorer
at full throttle?

It's not one jolly large cooling system. It's separated loops
and a wax plug. Accessory heat is not available immediately,
because the car design gives priority to warming up the oil.
Once the engine is sufficiently warm, the accessory loop opens
and heat is available in the cabin. The wax plug measures the
temperature and the wax melts when the coolant is warm enough.

And various posh cars, have other subsystems tied into the
main cooling loop. Maybe the oil in the transmission is
being heated or regulated by using the cooling system.

Some cars even have electrically heated catalytic converters,
which is a feature used to achieve very low lifecycle emissions
at the exhaust. Most regular cars just wait for the engine
to warm up, and the emissions gradually come down as a result.
But some cars waste energy heating the cat for the first minute
or two, to drive down the emissions right after start.

There was a design some years ago (never used in a production vehicle
AFAIK) that ran the engine very rich on start-up and had an additional
spark-plug at the catalytic converter to provide almost immediate
heating of the catalyst).